SimTX Wiki - User contributions [en]

Main Page

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<strong>Welcome to the SimTX Wiki</strong>, the documentation for the SimTX radio simulation platform. These pages cover the '''SimTX Transmitter''' desktop application: station setup, transmitting, antennas and the calculations behind them.

== Start here ==
* [[SimTX Transmitter]]: what the software is and how it fits together
* [[Getting Started]]: connect to a server and make a first transmission
* [[Transmitter Interface]]: reference for every control in the window

== Operating ==
* [[Modulation Modes]]
* [[Transmission Sources]]
* [[Radio Presets]]
* [[Advanced Transmitter Settings]]
* [[Station Configuration]]
* [[Sessions and Queueing]]
* [[Power Amplifier Behaviour]]
* [[SWR and Transmitter Protection]]

== Antennas ==
* [[Antenna System]]: overview and configuration
* Types: [[Dipole Antenna]] · [[Inverted-V Antenna]] · [[Vertical Antenna]] · [[Yagi Antenna]] · [[Full-Wave Loop Antenna]] · [[Longwire Antenna]] · [[Beverage Antenna]] · [[End-Fed Half-Wave Antenna]]
* [[NEC File Import]]: custom antenna geometries
* [[Antenna Calculations]]: sizing, decibels, SWR arithmetic

== Understanding the simulation ==
* [[Propagation Basics]]: groundwave, skywave, MUF and LUF, noise, and whether a signal will be heard

== Community ==
* [[:Category:Radio Stations]]: station pages made by users, and how to add your own

Category:Radio Stations

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Pages about individual radio stations run by SimTX users.

== Adding your station ==
# Type your station's name in the search box and follow the "Create the page" link, or open <code>https://wiki.simtx.net/index.php/Your_Station_Name</code> directly.
# Describe the station. A useful structure: callsign, frequency and schedule, location, equipment (radio preset and power), antenna, programme description.
# End the page with <code><nowiki>[[Category:Radio Stations]]</nowiki></code> so it appears in the list below automatically.

Propagation Basics

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SimTX simulates realistic radio propagation between stations, including the ionosphere, time of day, season, solar and geomagnetic activity, ground quality and receiver noise. This page explains, from the operator's point of view, what determines whether a transmission is heard at a given distance.

== Two ways a signal travels ==
* '''Groundwave''': the signal follows the ground outward from the antenna. It dominates short range (out to a few tens of kilometers on all bands, farther on lower frequencies) and favours '''vertically polarized''' antennas and good ground (sea water is best). Groundwave range shrinks quickly as frequency rises; on the higher HF bands it is essentially local.
* '''Skywave''': the signal refracts off the ionosphere and returns to Earth hundreds to thousands of kilometers away. This is how HF covers distance. Multiple hops extend the range further at the cost of extra loss.

Between the end of groundwave and the first skywave return there can be a '''skip zone''' where the station is inaudible even though it is heard both closer and farther away.

== The frequency window: LUF and MUF ==
For any skywave path at any moment there is a usable frequency window:
* Above the '''maximum usable frequency (MUF)''' the ionosphere no longer bends the signal back; it escapes into space.
* Below the '''lowest usable frequency (LUF)''' absorption in the lower ionosphere eats the signal.
The window moves constantly:
* The MUF rises with solar activity and during daytime, and is generally higher on paths toward the equator than at high latitudes.
* The LUF rises during daylight (absorption is a daytime phenomenon) and drops at night, when very low frequencies open up.
* Frequencies just below the MUF usually propagate best; deep inside the window absorption grows toward the low end.

Rules of thumb that follow directly:
* '''Low bands (below about 5 MHz)''': night-time and short-to-medium range in daytime. Daytime long-distance work is largely absorbed.
* '''Middle bands (5 to 12 MHz)''': workable day and night; the default 4625 kHz falls here.
* '''High bands (above about 14 MHz)''': daytime and high solar activity; they close at night.
* Around dawn and dusk (the grey line), low and middle band paths along the terminator are enhanced.

== Short range via the ionosphere: NVIS ==
Coverage from roughly 50 to 500 km needs radiation that goes almost straight up and reflects back down (near-vertical incidence skywave). It requires a frequency comfortably below the vertical MUF (typically 2 to 8 MHz depending on conditions) and a '''high-angle antenna''': a low dipole, inverted-V or loop. This is the regime where "worse" antennas outperform beams.

== Long range ==
Distances beyond about 1000 km leave the antenna at '''low elevation angles'''. What helps: a low takeoff antenna (Yagi, vertical, high dipole), a frequency near the path MUF, and daylight positioning appropriate to the band. Multi-hop paths add loss per hop, so more power or better antennas are needed as distance grows.

== Noise at the receiver ==
Whether a signal is readable depends on how far it sits above the receiving station's noise floor:
* '''Atmospheric noise''' dominates the low bands and is much stronger at night and in disturbed conditions.
* '''Man-made noise''' depends on the receiver environment; a city location can be tens of decibels noisier than a quiet rural one.
* Noise grows with receiver bandwidth: narrow modes hear deeper.

== Mode sensitivity ==
Approximate signal-to-noise ratios needed for readable copy, from most to least sensitive:
{| class="wikitable"
! Mode !! Approximate required SNR
|-
| CW || around 0 dB
|-
| SSB (USB/LSB) || about 6 dB
|-
| AM || 8 to 10 dB
|-
| NFM / WFM || about 12 dB
|}
The spread matters: a path hopeless for FM can still carry CW comfortably. Narrow modes are the best probes of marginal propagation.

== Disturbances and fading ==
* Geomagnetic storms raise absorption, depress the MUF, destabilize high-latitude paths and add Doppler drift and spreading to signals. During storms, ionospheric signals can slowly march in frequency and fade rhythmically.
* Even on quiet days skywave signals fade continuously (multipath fading); deep fades of many decibels are normal and average out over time.
* Sporadic E can open surprising mid-range paths on high frequencies, mainly in local summer.

== Checklist: will I be heard at distance X? ==
# Under about 50 km: almost any setup works; vertical polarization helps most.
# 50 to 500 km: use a low band frequency below the day's vertical MUF and a high-angle antenna (NVIS).
# 500 to 3000 km: pick a band whose window is open for the time of day (lower at night, higher by day); a dipole at good height works.
# Beyond 3000 km: choose a frequency near the path MUF, use a low-takeoff antenna aimed at the target, and prefer sensitive modes.
# Always compare the required SNR of the mode with realistic noise at the receiving end; when in doubt, drop to a narrower mode rather than raising power.

[[Category:SimTX]]

SimTX Transmitter

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'''SimTX Transmitter''' is the operator client of the SimTX radio simulation platform. It lets a user configure a virtual radio station (callsign, location, transmitter, antenna) and transmit audio or data signals into a shared simulated radio spectrum hosted by a SimTX server. Receivers connected to the same server can tune to the transmission and hear it, subject to simulated antenna performance, propagation conditions and noise.

The transmitter does not emit real radio frequency energy. All modulation, amplifier behaviour and propagation are computed by the server; the client sends the station configuration and the source audio, and displays live measurements sent back by the server.

== Overview ==
A transmitter session works as follows:

# The operator starts the application and connects to a SimTX server (default port 5100).
# The station is configured: callsign, geographic location, frequency, power, modulation, transmission source and antenna.
# The operator presses '''Start TX'''. The server admits, queues or rejects the session depending on its session limits.
# While the session runs, the Radio Deck shows live measured values: forward and reflected power, SWR, ALC, amplifier temperature and audio buffer level.
# The session ends when the source finishes, the operator stops it, or the server ends it.

== Main topics ==
* [[Getting Started]]: installation, connecting to a server, first transmission
* [[Transmitter Interface]]: reference for every control in the application window
* [[Modulation Modes]]: supported modes and their bandwidths
* [[Transmission Sources]]: audio files, microphone, white noise, PipeWire, GNU Radio IQ
* [[Radio Presets]]: built-in transmitter characteristics, from clean lab exciters to overdriven CB rigs
* [[Advanced Transmitter Settings]]: the fifteen fine-tuning parameters
* [[Station Configuration]]: callsign, location and saving station presets
* [[Antenna System]]: how antennas behave and are configured, with a page per antenna type
* [[Antenna Calculations]]: resonant lengths, SWR, gain and loss arithmetic
* [[SWR and Transmitter Protection]]: what happens when the antenna is mismatched
* [[Power Amplifier Behaviour]]: heating, power foldback and permanent damage
* [[Sessions and Queueing]]: admission, queue positions, rejections and kicks
* [[Propagation Basics]]: what determines whether a signal is heard at a distance

== What SimTX simulates ==
From the operator's point of view the simulation covers:
* Transmitter imperfections: compression, distortion, carrier leakage, hum, phase noise and more, selectable through [[Radio Presets]] or tuned individually.
* Realistic antennas: each antenna type has a genuine radiation pattern, feedpoint impedance and SWR that change with frequency, size, height and orientation. Custom antennas can be imported as NEC decks, see [[NEC File Import]].
* Amplifier thermodynamics: sustained transmission heats the finals, reduces output power and can permanently damage the amplifier, see [[Power Amplifier Behaviour]].
* Radio propagation between stations, including ionospheric effects, time of day and distance, see [[Propagation Basics]].

[[Category:SimTX]]

NEC File Import

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Custom antennas can be imported as '''NEC decks''', the standard text format used by antenna modelling tools such as 4nec2 and EZNEC. The '''Import NEC...''' button in the Antenna section loads a deck; '''Use built-in''' reverts to the selected built-in type.

== Supported format ==
Plain NEC-2 style cards, coordinates in meters. Accepted file extensions: <code>.nec</code>, <code>.ez</code>, <code>.txt</code>.

{| class="wikitable"
! Card !! Support
|-
| GW || Wire definition (tag, segments, endpoints, radius). A radius of 0 defaults to 1 mm.
|-
| GS || Scale factor, applied to all coordinates and radii.
|-
| GE || Geometry end; its ground flag is honoured.
|-
| GN || Ground description; mapped to the nearest of the simulator's ground categories (perfect, salt water, fresh water, good, average, very poor).
|-
| EX || Excitation; used to locate the feedpoint on the tagged wire.
|-
| FR || Design frequency.
|-
| EN || End of deck.
|-
| CM, CE || Comments, ignored.
|}

'''Not supported''': lumped loads (LD), transmission line cards (TL) and other advanced cards are ignored. Antennas that depend on loading coils or line matching will therefore behave differently than in a full NEC package. A deck with no GW card is rejected.

== Tips ==
* Model in a dedicated NEC tool, verify the pattern and impedance there, then export and import the deck.
* If no excitation card is present the feed defaults to the center of the first wire.

[[Category:Antennas]] [[Category:SimTX]]

End-Fed Half-Wave Antenna

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The '''end-fed half-wave''' (EFHW) is a half-wavelength wire fed at one end through a 49:1 impedance transformer (unun). It is the default antenna in SimTX, configured as a 32.5 m wire at 10 m height, which is close to resonance at the default frequency of 4625 kHz.

== Configuration ==
A single wire hung from the configured height and fed at one end through the 49:1 transformer. Default wire length 32.5 m.

== Characteristics ==
* Typical gain around 2.1 dBi with a takeoff angle around 28 degrees at typical heights.
* Because the end of a half-wave wire presents a very high impedance, the 49:1 transformer is required to bring it near 50 ohms. The transformer costs a small insertion loss (about half a decibel, growing when the match is poor).
* Multi-band behaviour: like all end-fed half-waves it also presents usable matches near integer multiples of its fundamental, with slightly worse match and higher transformer loss on the harmonics.
* Practically convenient: one support, feedpoint at the end.

== Sizing ==
The wire should be an electrical half-wave: roughly 143 to 150 divided by the frequency in MHz, in meters. The default 32.5 m corresponds to a fundamental near 4.6 MHz, which is why the application defaults to 4625 kHz. Operating the default antenna at a very different frequency (for example 7.1 MHz, between its harmonics) produces a severe mismatch and almost no radiated signal; either change the wire length or pick a frequency near a harmonic.

== When to use ==
As a realistic general-purpose wire antenna, especially when simulating portable or space-constrained stations. For best single-band performance a resonant [[Dipole Antenna]] at good height still has the edge.

[[Category:Antennas]]

Beverage Antenna

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The '''Beverage''' is a travelling-wave antenna: a very long, very low wire, classically used for low-band reception. It is highly directional along the wire.

== Configuration ==
A single straight wire along the azimuth, mounted very low; the height is limited to 3 m regardless of the height setting, reflecting how Beverages are built. Default length 80 m; a length of 0 selects two wavelengths at the operating frequency, and real Beverages are typically one to several wavelengths long.

== Characteristics ==
* Typical gain figure around 8 dBi of directivity along the wire with a very low takeoff angle around 8 degrees.
* As a travelling-wave antenna it is inherently mismatched and lossy as a transmitting antenna: expect a permanently mediocre SWR (around 2.8) and note the high default feedline loss (2 dB). Real stations use Beverages for receive, not transmit.
* Very directive front lobe toward the azimuth heading; point it at the target region.
* Works best over average to poor ground.

== When to use ==
Mostly for experimentation and for simulating receive-style directivity on the low bands. As a transmit antenna it is deliberately inefficient; a [[Vertical Antenna]] radiates far better on the same bands.

[[Category:Antennas]]

Longwire Antenna

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The '''longwire''' is a straight wire several wavelengths long, fed at one end. Unlike a random end-fed wire, a true longwire develops directivity along the wire direction.

== Configuration ==
A single horizontal wire running along the azimuth, default length 21 m; a length of 0 selects two wavelengths at the operating frequency.

== Characteristics ==
* Typical gain around 4 dBi with lobes that press toward the wire direction as the wire gets electrically longer.
* Typical takeoff angle around 20 degrees.
* Multi-band by nature: it presents workable (though rarely excellent) matches on many frequencies, with SWR varying between harmonics. Expect a rougher match than a resonant dipole; a tuner-style loss is reflected in the higher default feedline loss (1.2 dB).
* Directional along the wire run: point the azimuth roughly toward the target.

== When to use ==
When simulating a simple field or shortwave-listener style station with one long wire, or when multi-band capability matters more than a clean match. For a serious single band, a resonant [[Dipole Antenna]] usually wins.

[[Category:Antennas]]

Full-Wave Loop Antenna

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The '''full-wave loop''' is a closed wire loop whose circumference is one wavelength, mounted in a vertical plane and fed at the bottom.

== Configuration ==
The loop stands in a vertical plane and is fed at the bottom; the length field is labelled '''Circumference'''. The default is 1.0 m, which is only sensible for very high frequencies; set 0 to get a full-wave circumference for the operating frequency, or enter it explicitly.

== Characteristics ==
* Typical gain around 1.5 dBi with a high takeoff angle around 55 degrees: primarily a short and medium range antenna.
* Broadside pattern (perpendicular to the loop plane), controlled by the azimuth setting, but lobes are broad.
* Distinctly '''narrowband''': the SWR is excellent at resonance and degrades quickly off frequency. Retune (adjust circumference) when changing frequency by more than a fraction of a percent.
* Quiet and clean pattern; a classic choice for regional nets.

== Sizing ==
A full-wave circumference in meters is approximately 300 divided by the frequency in MHz (see [[Antenna Calculations]]). Example: about 84 m at 3.6 MHz, about 42 m at 7.1 MHz.

== When to use ==
For reliable short and medium range ionospheric coverage on a fixed frequency. Poor choice for frequency-agile operation because of the narrow match.

[[Category:Antennas]]

Yagi Antenna

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The '''Yagi''' (Yagi-Uda) is a directional beam antenna: a driven element plus a reflector behind it and one or more directors in front. SimTX provides a '''3-element''' and a '''5-element''' version.

== Configuration ==
The boom points along the configured azimuth; elements are horizontal. The driven element length defaults to 10.1 m; a value of 0 sizes the antenna for the operating frequency.

== Characteristics ==
{| class="wikitable"
! Version !! Typical gain !! Typical takeoff angle
|-
| 3 elements || 7.5 dBi || 14°
|-
| 5 elements || 10.2 dBi || 10°
|}
* Strongly directional: most of the power goes toward the azimuth heading, with a large front-to-back advantage. Aim it at the target region; a misaimed Yagi is worse than a dipole.
* Low takeoff angles at reasonable heights make Yagis the tool of choice for long-distance work on the higher HF bands.
* Wider SWR bandwidth than simple wire antennas, the 5-element version widest.

== Practical notes ==
* Set '''Azimuth''' to the great-circle bearing toward the target area (0 is north, 90 is east).
* A full-size Yagi for the low bands is enormous (a 3.6 MHz driven element is about 40 m); realistically they are used from roughly 14 MHz upward.
* Height still matters: mount at least half a wavelength up for the advertised low-angle performance.

== When to use ==
For point-to-point and long-distance coverage toward a known direction on the higher bands. For all-around coverage use a [[Dipole Antenna]], [[Vertical Antenna]] or [[Full-Wave Loop Antenna]] instead.

[[Category:Antennas]]

Vertical Antenna

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The '''vertical''' is a quarter-wave monopole worked against ground. It is omnidirectional and radiates well at low elevation angles, which favours distance.

== Configuration ==
A single vertical radiator fed at the base. The element length defaults to 5.1 m; a length of 0 selects a resonant quarter-wave element for the operating frequency. The azimuth field is disabled because the pattern is the same in all directions.

== Characteristics ==
* Typical gain around 1.8 dBi, evenly in all compass directions.
* Low typical takeoff angle around 18 degrees: good for long-distance ionospheric paths despite the modest gain figure.
* Vertical polarization, which is strongly favoured on short-range ground-hugging paths. For local and regional coverage below a few hundred kilometers on the lower bands, a vertical often outperforms much "bigger" horizontal antennas.
* Ground quality matters more than for horizontal antennas; poor ground raises losses.

== Sizing ==
A resonant quarter-wave element in meters is approximately 71.5 divided by the frequency in MHz, half the dipole length (see [[Antenna Calculations]]). Example: about 10 m at 7.1 MHz.

== When to use ==
Pick the vertical for omnidirectional low-angle coverage, groundwave range on the low bands, or when there is no room for long horizontal wires. Its weakness is medium-range ionospheric coverage, where high-angle radiators (dipole, inverted-V, loop) do better.

[[Category:Antennas]]

Inverted-V Antenna

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The '''inverted-V''' is a variant of the [[Dipole Antenna]] supported at a single central point, with the two legs sloping down toward the ends. It needs only one mast, which makes it a common practical compromise.

== Configuration ==
The feedpoint sits at the apex (the configured height) and the two legs slope down at roughly 40 degrees. The default length is 10.8 m; a length of 0 selects the resonant length for the operating frequency.

== Characteristics ==
* Typical gain around 1.8 dBi, a little below a flat dipole at the same apex height, because the average wire height is lower.
* Nearly omnidirectional; the sloping legs fill in the nulls a flat dipole has off its ends.
* Typical takeoff angle around 40 degrees: well suited to short and medium range ionospheric coverage.
* Slightly wider SWR bandwidth than a flat dipole.

== When to use ==
Choose the inverted-V when simulating a station with a single support, for regional coverage, or when an omnidirectional pattern is preferred over the dipole's broadside preference. For long-distance work a high flat dipole or a Yagi performs better.

[[Category:Antennas]]

Dipole Antenna

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The '''dipole''' is a half-wave wire antenna fed at its center. It is the classic reference antenna for HF work: simple, predictable and effective.

== Configuration ==
The wire runs horizontally along the azimuth direction and is fed in the center. The default wire length is 10.1 m; a length of 0 selects the resonant half-wave length for the operating frequency automatically.

== Characteristics ==
* Typical gain around 5.5 dBi over ground, broadside to the wire (peaks perpendicular to the wire run).
* Non-directional in practice: a figure-eight pattern with broad lobes and shallow nulls off the wire ends.
* Typical takeoff angle around 30 degrees at the default 10 m height. Radiation angle depends strongly on height, see below.
* Moderate bandwidth: SWR stays reasonable over several percent of the center frequency; odd multiples of the resonant frequency are also usable.

== Height ==
Height above ground is the dominant tuning knob:
* Below roughly a quarter wavelength, the dipole radiates mostly straight up. That is excellent for short-range regional coverage (a few hundred kilometers via near-vertical ionospheric reflection) and poor for long distance.
* Around half a wavelength and above, a strong low-angle lobe forms and long-distance performance improves markedly.

== Sizing ==
A practical resonant half-wave length in meters is approximately 143 divided by the frequency in MHz (see [[Antenna Calculations]]). Examples: about 40 m at 3.6 MHz, about 20 m at 7.1 MHz, about 10 m at 14.2 MHz. Leaving the length at 0 lets SimTX use the resonant length directly.

== When to use ==
A resonant dipole at a sensible height is a strong general-purpose choice on any HF band and a good baseline against which to compare other antennas.

[[Category:Antennas]]

SWR and Transmitter Protection

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The standing wave ratio (SWR) describes how well the antenna system is matched to the transmitter's 50 ohm output. It is shown live on the '''SWR''' meter of the Radio Deck, together with forward ('''FWD''') and reflected ('''REF''') power.

== What SWR means ==
* '''SWR 1.0''' is a perfect match: all forward power reaches the antenna.
* '''SWR 2.0''' reflects about 11 percent of the power (about 0.5 dB loss).
* '''SWR 3.0''' reflects 25 percent (about 1.25 dB loss).
* Very high SWR means the antenna barely accepts power at the operating frequency.
See [[Antenna Calculations]] for the arithmetic.

== Where mismatch comes from ==
SWR in SimTX behaves as it does in reality:
* Operating far from the antenna's resonant frequency raises SWR quickly. A wire length of 0 in the antenna form means "resonant at the operating frequency" and gives a good match on that frequency.
* Antenna height, ground and geometry shift the feedpoint impedance.
* Narrowband antennas (notably the full-wave loop) show a good match only over a small frequency range.
* End-fed antennas are matched through a 49:1 transformer, which adds a small loss of its own, see [[End-Fed Half-Wave Antenna]].

== Transmitter protection ==
Like a real transceiver, the simulated transmitter folds back output power into a bad match to protect its finals:
* Protection begins at about '''SWR 2.5'''.
* Above that, output power is reduced progressively; a severe mismatch can cost several decibels on top of the mismatch loss itself.
The result is visible as reduced FWD power and reduced signal at receivers.

== Practical advice ==
* After changing frequency, check the SWR meter before a long transmission. The deck shows a local estimate even before the session starts.
* Match the antenna to the band: set the wire length near resonance (or leave it at 0 for automatic resonant length), see [[Antenna Calculations]].
* A modest SWR up to about 2 is normal and costs little. Chasing a perfect 1.0 is rarely worth it.

[[Category:SimTX]]

Antenna System

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The antenna is the most influential part of a SimTX station. Antenna choice therefore changes gain, directionality, takeoff angle, SWR and ultimately who can hear the transmission.

== Configuration fields ==
{| class="wikitable"
! Field !! Meaning
|-
| Type || One of the built-in antenna types below, or a custom geometry via [[NEC File Import]].
|-
| Wire Length (m) || The main dimension. Its label adapts to the type (circumference for the loop, element length for the vertical, driven element for the Yagis). '''0 means resonant at the operating frequency''': the length is derived automatically.
|-
| Height (m) || Height of the feedpoint or apex above ground. Height strongly shapes the vertical radiation pattern of horizontal antennas: low antennas radiate upward (short range), high antennas radiate at low angles (long range).
|-
| Azimuth (°) || Orientation, 0 is north, 90 is east. For directional antennas this is the pointing direction; for wire antennas it is the direction the wire runs. Disabled for the vertical.
|-
| Feedline Loss (dB) || Fixed loss of the cable between transmitter and antenna. Subtracted from the radiated signal in both cases.
|}

== Built-in antenna types ==
{| class="wikitable"
! Type !! Typical gain (dBi) !! Directional !! Typical takeoff angle !! Default length (m) !! Default feedline loss (dB) !! Page
|-
| Dipole || 5.5 || No || 30° || 10.1 || 1.0 || [[Dipole Antenna]]
|-
| Inverted-V || 1.8 || No || 40° || 10.8 || 1.0 || [[Inverted-V Antenna]]
|-
| Vertical || 1.76 || No || 18° || 5.1 || 0.5 || [[Vertical Antenna]]
|-
| Yagi 3-element || 7.5 || Yes || 14° || 10.1 || 0.8 || [[Yagi Antenna]]
|-
| Yagi 5-element || 10.2 || Yes || 10° || 10.1 || 0.8 || [[Yagi Antenna]]
|-
| Full-wave Loop || 1.5 || No || 55° || 1.0 || 0.3 || [[Full-Wave Loop Antenna]]
|-
| Longwire || 4.0 || Yes || 20° || 21.0 || 1.2 || [[Longwire Antenna]]
|-
| Beverage || 8.0 || Yes || 8° || 80.0 || 2.0 || [[Beverage Antenna]]
|-
| EFHW + 49:1 unun || 2.1 || No || 28° || 32.5 || 0.6 || [[End-Fed Half-Wave Antenna]]
|}
The gain and takeoff figures are typical values; actual performance varies with frequency, length, height and azimuth.

== How the antenna affects the link ==
What reaches a receiver depends on the antenna gain in the exact direction and elevation of the path, minus feedline loss, mismatch loss and any protection foldback, at both ends of the link. Consequences:

* '''Takeoff angle matters as much as gain.''' Long-distance ionospheric paths leave at low elevation angles; short-range paths need high-angle radiation. An antenna with modest gain at the right angle beats a high-gain antenna pointed at the wrong angle. See [[Propagation Basics]].
* '''Directional antennas must be aimed.''' A 5-element Yagi pointed away from the receiver can be worse than a dipole.
* '''Polarization matters.''' Ground-hugging short-range propagation strongly favours vertical polarization; horizontal antennas radiate very little at grazing angles. On ionospheric paths polarization is scrambled and costs a fixed few decibels regardless of antenna.
* '''Height shapes the pattern.''' Raising a horizontal antenna lowers its main lobe. As a rule of thumb, half a wavelength of height gives a useful low-angle lobe.

== Local estimate ==
The Radio Deck shows the expected peak gain (dBi) and the VSWR at 50 ohms for the current configuration before any session starts, recomputed whenever frequency, power or antenna fields change. Use it to sanity-check a design before transmitting.

== See also ==
* [[Antenna Calculations]]
* [[NEC File Import]]
* [[SWR and Transmitter Protection]]

[[Category:SimTX]] [[Category:Antennas]]

SimTX Transmitter

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'''SimTX Transmitter''' is the operator client of the SimTX radio simulation platform. It lets a user configure a virtual radio station (callsign, location, transmitter, antenna) and transmit audio or data signals into a shared simulated radio spectrum hosted by a SimTX server. Receivers connected to the same server can tune to the transmission and hear it, subject to simulated antenna performance, propagation conditions and noise.

The transmitter does not emit real radio frequency energy. All modulation, amplifier behaviour and propagation are computed by the server; the client sends the station configuration and the source audio, and displays live measurements sent back by the server.

== Overview ==
A transmitter session works as follows:

# The operator starts the application and connects to a SimTX server (default port 5100).
# The station is configured: callsign, geographic location, frequency, power, modulation, transmission source and antenna.
# The operator presses '''Start TX'''. The server admits, queues or rejects the session depending on its session limits.
# While the session runs, the Radio Deck shows live measured values: forward and reflected power, SWR, ALC, amplifier temperature and audio buffer level.
# The session ends when the source finishes, the operator stops it, or the server ends it.

== Main topics ==
* [[Getting Started]]: installation, connecting to a server, first transmission
* [[Transmitter Interface]]: reference for every control in the application window
* [[Modulation Modes]]: supported modes and their bandwidths
* [[Transmission Sources]]: audio files, microphone, white noise, PipeWire, GNU Radio IQ
* [[Radio Presets]]: built-in transmitter characteristics, from clean lab exciters to overdriven CB rigs
* [[Advanced Transmitter Settings]]: the fifteen fine-tuning parameters
* [[Station Configuration]]: callsign, location and saving station presets
* [[Antenna System]]: how antennas are modelled and configured, with a page per antenna type
* [[Antenna Calculations]]: resonant lengths, SWR, gain and loss arithmetic
* [[SWR and Transmitter Protection]]: what happens when the antenna is mismatched
* [[Power Amplifier Behaviour]]: heating, power foldback and permanent damage
* [[Sessions and Queueing]]: admission, queue positions, rejections and kicks
* [[Propagation Basics]]: what determines whether a signal is heard at a distance

== What SimTX simulates ==
From the operator's point of view the simulation covers:
* Transmitter imperfections: compression, distortion, carrier leakage, hum, phase noise and more, selectable through [[Radio Presets]] or tuned individually.
* Realistic antennas: each antenna type has a genuine radiation pattern, feedpoint impedance and SWR that change with frequency, size, height and orientation. Custom antennas can be imported as NEC decks, see [[NEC File Import]].
* Amplifier thermodynamics: sustained transmission heats the finals, reduces output power and can permanently damage the amplifier, see [[Power Amplifier Behaviour]].
* Radio propagation between stations, including ionospheric effects, time of day and distance, see [[Propagation Basics]].

[[Category:SimTX]]

NEC File Import

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Clanker: Remove What happens on import section

Custom antennas can be imported as '''NEC decks''', the standard text format used by antenna modelling tools such as 4nec2 and EZNEC. The '''Import NEC...''' button in the Antenna section loads a deck; '''Use built-in''' reverts to the selected built-in type.

== Supported format ==
Plain NEC-2 style cards, coordinates in meters. Accepted file extensions: <code>.nec</code>, <code>.ez</code>, <code>.txt</code>.

{| class="wikitable"
! Card !! Support
|-
| GW || Wire definition (tag, segments, endpoints, radius). A radius of 0 defaults to 1 mm.
|-
| GS || Scale factor, applied to all coordinates and radii.
|-
| GE || Geometry end; its ground flag is honoured.
|-
| GN || Ground description; mapped to the nearest of the simulator's ground categories (perfect, salt water, fresh water, good, average, very poor).
|-
| EX || Excitation; used to locate the feedpoint on the tagged wire.
|-
| FR || Design frequency.
|-
| EN || End of deck.
|-
| CM, CE || Comments, ignored.
|}

'''Not supported''': lumped loads (LD), transmission line cards (TL) and other advanced cards are ignored. Antennas that depend on loading coils or line matching will therefore solve differently than in a full NEC package. A deck with no GW card is rejected.

== Tips ==
* Model in a dedicated NEC tool, verify the pattern and impedance there, then export and import the deck.
* Keep the geometry moderate in size; extremely finely segmented models gain nothing and solve slowly.
* If no excitation card is present the feed defaults to the center of the first wire.

[[Category:Antennas]] [[Category:SimTX]]

Propagation Basics

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Clanker: Remove WSPR and FT8 references

SimTX simulates realistic radio propagation between stations, including the ionosphere, time of day, season, solar and geomagnetic activity, ground quality and receiver noise. This page explains, from the operator's point of view, what determines whether a transmission is heard at a given distance. It intentionally describes behaviour, not the internal models.

== Two ways a signal travels ==
* '''Groundwave''': the signal follows the ground outward from the antenna. It dominates short range (out to a few tens of kilometers on all bands, farther on lower frequencies) and favours '''vertically polarized''' antennas and good ground (sea water is best). Groundwave range shrinks quickly as frequency rises; on the higher HF bands it is essentially local.
* '''Skywave''': the signal refracts off the ionosphere and returns to Earth hundreds to thousands of kilometers away. This is how HF covers distance. Multiple hops extend the range further at the cost of extra loss.

Between the end of groundwave and the first skywave return there can be a '''skip zone''' where the station is inaudible even though it is heard both closer and farther away.

== The frequency window: LUF and MUF ==
For any skywave path at any moment there is a usable frequency window:
* Above the '''maximum usable frequency (MUF)''' the ionosphere no longer bends the signal back; it escapes into space.
* Below the '''lowest usable frequency (LUF)''' absorption in the lower ionosphere eats the signal.
The window moves constantly:
* The MUF rises with solar activity and during daytime, and is generally higher on paths toward the equator than at high latitudes.
* The LUF rises during daylight (absorption is a daytime phenomenon) and drops at night, when very low frequencies open up.
* Frequencies just below the MUF usually propagate best; deep inside the window absorption grows toward the low end.

Rules of thumb that follow directly:
* '''Low bands (below about 5 MHz)''': night-time and short-to-medium range in daytime. Daytime long-distance work is largely absorbed.
* '''Middle bands (5 to 12 MHz)''': workable day and night; the default 4625 kHz falls here.
* '''High bands (above about 14 MHz)''': daytime and high solar activity; they close at night.
* Around dawn and dusk (the grey line), low and middle band paths along the terminator are enhanced.

== Short range via the ionosphere: NVIS ==
Coverage from roughly 50 to 500 km needs radiation that goes almost straight up and reflects back down (near-vertical incidence skywave). It requires a frequency comfortably below the vertical MUF (typically 2 to 8 MHz depending on conditions) and a '''high-angle antenna''': a low dipole, inverted-V or loop. This is the regime where "worse" antennas outperform beams.

== Long range ==
Distances beyond about 1000 km leave the antenna at '''low elevation angles'''. What helps: a low takeoff antenna (Yagi, vertical, high dipole), a frequency near the path MUF, and daylight positioning appropriate to the band. Multi-hop paths add loss per hop, so more power or better antennas are needed as distance grows.

== Noise at the receiver ==
Whether a signal is readable depends on how far it sits above the receiving station's noise floor:
* '''Atmospheric noise''' dominates the low bands and is much stronger at night and in disturbed conditions.
* '''Man-made noise''' depends on the receiver environment; a city location can be tens of decibels noisier than a quiet rural one.
* Noise grows with receiver bandwidth: narrow modes hear deeper.

== Mode sensitivity ==
Approximate signal-to-noise ratios needed for readable copy, from most to least sensitive:
{| class="wikitable"
! Mode !! Approximate required SNR
|-
| CW || around 0 dB
|-
| SSB (USB/LSB) || about 6 dB
|-
| AM || 8 to 10 dB
|-
| NFM / WFM || about 12 dB
|}
The spread matters: a path hopeless for FM can still carry CW comfortably. Narrow modes are the best probes of marginal propagation.

== Disturbances and fading ==
* Geomagnetic storms raise absorption, depress the MUF, destabilize high-latitude paths and add Doppler drift and spreading to signals. During storms, ionospheric signals can slowly march in frequency and fade rhythmically.
* Even on quiet days skywave signals fade continuously (multipath fading); deep fades of many decibels are normal and average out over time.
* Sporadic E can open surprising mid-range paths on high frequencies, mainly in local summer.

== Checklist: will I be heard at distance X? ==
# Under about 50 km: almost any setup works; vertical polarization helps most.
# 50 to 500 km: use a low band frequency below the day's vertical MUF and a high-angle antenna (NVIS).
# 500 to 3000 km: pick a band whose window is open for the time of day (lower at night, higher by day); a dipole at good height works.
# Beyond 3000 km: choose a frequency near the path MUF, use a low-takeoff antenna aimed at the target, and prefer sensitive modes.
# Always compare the required SNR of the mode with realistic noise at the receiving end; when in doubt, drop to a narrower mode rather than raising power.

[[Category:SimTX]]

Category:Antennas

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Clanker: Create category page

Antenna types, modelling and calculations for the SimTX Transmitter. See [[Antenna System]] for the overview.

Category:SimTX

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Clanker: Create category page

Documentation for the SimTX Transmitter application: guides, interface reference and operating topics.

Modulation Modes

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Clanker: Remove WSPR and FT8

The SimTX Transmitter supports the following modulation modes. The '''Auto''' bandwidth option fills the typical bandwidth for the selected mode; the bandwidth field accepts any value down to the mode's minimum.

{| class="wikitable"
! Mode !! Full name !! Typical bandwidth !! Minimum bandwidth !! Audio range
|-
| AM (full carrier) || Amplitude modulation, double sideband, full carrier || 10 kHz || 160 Hz || 80 to 4500 Hz
|-
| AM (suppressed carrier) || Double sideband, suppressed carrier || 6 kHz || 160 Hz || 100 to 2800 Hz
|-
| USB || Upper sideband || 2700 Hz || 300 Hz || 350 to 2700 Hz
|-
| LSB || Lower sideband || 2700 Hz || 300 Hz || 350 to 2700 Hz
|-
| CW || Continuous wave (Morse keying) || 150 Hz || 50 Hz || n/a
|-
| NFM || Narrowband FM || 12.5 kHz || 2.5 kHz || 200 to 3000 Hz
|-
| WFM || Wideband FM (broadcast) || 180 kHz || 50 kHz || 30 Hz to 15 kHz
|-
| IQ || External complex IQ input || 48 kHz || 100 Hz || n/a
|}

== Mode notes ==
* '''USB and LSB''' are suppressed-carrier modes. The carrier leak and opposite-sideband suppression settings in [[Advanced Transmitter Settings]] control how imperfect the suppression is. By convention LSB is used below 10 MHz and USB above, but SimTX does not enforce this.
* '''AM''' modes expose the AM modulation index setting. An index above 1.0 is overmodulation and produces audible distortion and splatter.
* '''CW''' exposes the key rise time setting. Very short rise times produce key clicks that widen the occupied bandwidth. CW is also the most sensitive mode: its narrow bandwidth lets it remain readable on paths where voice modes fail, see [[Propagation Basics]].
* '''NFM and WFM''' are constant-envelope modes; they are less affected by amplifier compression but need considerably more signal at the receiver than SSB. WFM supports stereo when fed from the PipeWire Stereo source.
* '''IQ''' passes externally generated complex baseband (for example from GNU Radio) straight to the channel. Selecting the GNU Radio IQ source forces this mode.

== Field interactions ==
* The low-cut field is editable for USB, LSB, both AM modes, NFM and WFM.
* Opposite-sideband suppression applies to USB and LSB only.
* Carrier leak applies to USB, LSB and suppressed-carrier AM.
* AM index applies to the two AM modes.
* CW rise time applies to CW only.
* PipeWire Stereo forces WFM; GNU Radio IQ forces IQ.

[[Category:SimTX]]

Main Page

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Clanker: Replace default main page with SimTX navigation

Propagation Basics

2026-07-05T08:47:35Z

Clanker: Create propagation basics page

SimTX simulates realistic radio propagation between stations, including the ionosphere, time of day, season, solar and geomagnetic activity, ground quality and receiver noise. This page explains, from the operator's point of view, what determines whether a transmission is heard at a given distance. It intentionally describes behaviour, not the internal models.

== Two ways a signal travels ==
* '''Groundwave''': the signal follows the ground outward from the antenna. It dominates short range (out to a few tens of kilometers on all bands, farther on lower frequencies) and favours '''vertically polarized''' antennas and good ground (sea water is best). Groundwave range shrinks quickly as frequency rises; on the higher HF bands it is essentially local.
* '''Skywave''': the signal refracts off the ionosphere and returns to Earth hundreds to thousands of kilometers away. This is how HF covers distance. Multiple hops extend the range further at the cost of extra loss.

Between the end of groundwave and the first skywave return there can be a '''skip zone''' where the station is inaudible even though it is heard both closer and farther away.

== The frequency window: LUF and MUF ==
For any skywave path at any moment there is a usable frequency window:
* Above the '''maximum usable frequency (MUF)''' the ionosphere no longer bends the signal back; it escapes into space.
* Below the '''lowest usable frequency (LUF)''' absorption in the lower ionosphere eats the signal.
The window moves constantly:
* The MUF rises with solar activity and during daytime, and is generally higher on paths toward the equator than at high latitudes.
* The LUF rises during daylight (absorption is a daytime phenomenon) and drops at night, when very low frequencies open up.
* Frequencies just below the MUF usually propagate best; deep inside the window absorption grows toward the low end.

Rules of thumb that follow directly:
* '''Low bands (below about 5 MHz)''': night-time and short-to-medium range in daytime. Daytime long-distance work is largely absorbed.
* '''Middle bands (5 to 12 MHz)''': workable day and night; the default 4625 kHz falls here.
* '''High bands (above about 14 MHz)''': daytime and high solar activity; they close at night.
* Around dawn and dusk (the grey line), low and middle band paths along the terminator are enhanced.

== Short range via the ionosphere: NVIS ==
Coverage from roughly 50 to 500 km needs radiation that goes almost straight up and reflects back down (near-vertical incidence skywave). It requires a frequency comfortably below the vertical MUF (typically 2 to 8 MHz depending on conditions) and a '''high-angle antenna''': a low dipole, inverted-V or loop. This is the regime where "worse" antennas outperform beams.

== Long range ==
Distances beyond about 1000 km leave the antenna at '''low elevation angles'''. What helps: a low takeoff antenna (Yagi, vertical, high dipole), a frequency near the path MUF, and daylight positioning appropriate to the band. Multi-hop paths add loss per hop, so more power or better antennas are needed as distance grows.

== Noise at the receiver ==
Whether a signal is readable depends on how far it sits above the receiving station's noise floor:
* '''Atmospheric noise''' dominates the low bands and is much stronger at night and in disturbed conditions.
* '''Man-made noise''' depends on the receiver environment; a city location can be tens of decibels noisier than a quiet rural one.
* Noise grows with receiver bandwidth: narrow modes hear deeper.

== Mode sensitivity ==
Approximate signal-to-noise ratios needed for readable copy, from most to least sensitive:
{| class="wikitable"
! Mode !! Approximate required SNR
|-
| WSPR || −31 dB (decodes far below audible)
|-
| FT8 || −21 dB
|-
| CW || around 0 dB
|-
| SSB (USB/LSB) || about 6 dB
|-
| AM || 8 to 10 dB
|-
| NFM / WFM || about 12 dB
|}
The spread is enormous: a path hopeless for FM can still carry FT8 comfortably. Digital weak-signal modes are the best probes of marginal propagation.

== Disturbances and fading ==
* Geomagnetic storms raise absorption, depress the MUF, destabilize high-latitude paths and add Doppler drift and spreading to signals. During storms, ionospheric signals can slowly march in frequency and fade rhythmically.
* Even on quiet days skywave signals fade continuously (multipath fading); deep fades of many decibels are normal and average out over time.
* Sporadic E can open surprising mid-range paths on high frequencies, mainly in local summer.

== Checklist: will I be heard at distance X? ==
# Under about 50 km: almost any setup works; vertical polarization helps most.
# 50 to 500 km: use a low band frequency below the day's vertical MUF and a high-angle antenna (NVIS).
# 500 to 3000 km: pick a band whose window is open for the time of day (lower at night, higher by day); a dipole at good height works.
# Beyond 3000 km: choose a frequency near the path MUF, use a low-takeoff antenna aimed at the target, and prefer sensitive modes.
# Always compare the required SNR of the mode with realistic noise at the receiving end; when in doubt, drop to a narrower mode rather than raising power.

[[Category:SimTX]]

Antenna Calculations

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Clanker: Create antenna calculations page

This page collects the arithmetic needed to size antennas and reason about signal levels in SimTX. All formulas are standard radio engineering practice.

== Wavelength ==
Wavelength in meters:
: '''λ = 300 / f''', with f in MHz.
Examples: 4.625 MHz → 64.9 m; 7.1 MHz → 42.3 m; 14.2 MHz → 21.1 m.

== Resonant lengths ==
Practical wire antennas are slightly shorter than the free-space length because of end effects and wire thickness. Useful sizing rules (f in MHz, results in meters):
{| class="wikitable"
! Antenna !! Formula !! Example at 7.1 MHz
|-
| Half-wave dipole (total) || 143 / f || 20.1 m
|-
| Quarter-wave vertical || 71.5 / f || 10.1 m
|-
| Full-wave loop (circumference) || 300 / f || 42 m
|-
| End-fed half-wave (wire) || 143 to 150 / f || 20 to 21 m
|-
| Longwire, Beverage (guideline) || 2 × λ or more || 84 m or more
|}
In SimTX a wire length of '''0''' asks for the resonant length automatically; the formulas are mainly useful for setting explicit lengths and for understanding harmonic operation (a 40 m dipole for 3.6 MHz is also resonant near 10.8 MHz, three times the frequency).

== Decibels ==
* Power ratio in dB: '''10 · log10(P2 / P1)'''. Doubling power is +3 dB; ten times power is +10 dB.
* Absolute power: '''dBm = 10 · log10(P in W) + 30'''. Examples: 5 W = 37 dBm, 100 W = 50 dBm.
* One S-unit on a receiver corresponds to 6 dB, or a factor of 4 in power. Going from 100 W to 25 W costs one S-unit; from 100 W to 5 W costs about 13 dB, two S-units.

== Antenna gain ==
* Gain in this wiki and in the application is in '''dBi''', decibels relative to an isotropic radiator.
* Gain relative to a dipole (dBd) is dBi minus 2.15.
* Effective radiated power combines transmitter power, feedline loss and antenna gain. Example: 100 W (50 dBm) into 1 dB of feedline and a 7.5 dBi Yagi radiates the equivalent of 56.5 dBm, about 450 W, toward the main lobe.

== SWR, reflection and mismatch loss ==
Given a standing wave ratio S:
* Reflection coefficient: '''Γ = (S − 1) / (S + 1)'''
* Reflected power fraction: '''Γ²'''
* Mismatch loss: '''−10 · log10(1 − Γ²)''' dB
{| class="wikitable"
! SWR !! Reflected power !! Mismatch loss
|-
| 1.0 || 0 % || 0 dB
|-
| 1.5 || 4 % || 0.18 dB
|-
| 2.0 || 11 % || 0.51 dB
|-
| 3.0 || 25 % || 1.25 dB
|-
| 5.0 || 44 % || 2.55 dB
|-
| 10.0 || 67 % || 4.81 dB
|}
Mismatch loss alone is mild, but the transmitter's protection foldback adds further reduction above SWR 2.5, see [[SWR and Transmitter Protection]].

== Height in wavelengths ==
Convert antenna height to electrical height: '''h / λ'''. A dipole at 10 m is 0.24 λ high at 7.1 MHz (high-angle radiator, regional coverage) but 0.47 λ at 14.2 MHz (good low-angle lobe, long distance). This single number explains most of the difference in where a horizontal antenna performs well.

== Path budget in one line ==
Received signal = TX power (dBm) + TX antenna gain (dBi) − TX losses (feedline, mismatch, foldback) − path loss + RX antenna gain − RX losses. The signal is usable when it clears the receiver's noise floor by the margin the modulation mode needs, see [[Propagation Basics]].

[[Category:Antennas]] [[Category:SimTX]]

NEC File Import

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Clanker: Create NEC import page

Custom antennas can be imported as '''NEC decks''', the standard text format used by antenna modelling tools such as 4nec2 and EZNEC. The '''Import NEC...''' button in the Antenna section loads a deck; '''Use built-in''' reverts to the selected built-in type.

== What happens on import ==
The client parses the deck, solves it locally and reports the wire count, solve frequency, peak gain (dBi), feedpoint impedance and VSWR. The raw deck text is sent with the session so the server solves the exact same geometry. The deck is also stored in saved <code>.stxpreset</code> files.

== Supported format ==
Plain NEC-2 style cards, coordinates in meters. Accepted file extensions: <code>.nec</code>, <code>.ez</code>, <code>.txt</code>.

{| class="wikitable"
! Card !! Support
|-
| GW || Wire definition (tag, segments, endpoints, radius). A radius of 0 defaults to 1 mm.
|-
| GS || Scale factor, applied to all coordinates and radii.
|-
| GE || Geometry end; its ground flag is honoured.
|-
| GN || Ground description; mapped to the nearest of the simulator's ground categories (perfect, salt water, fresh water, good, average, very poor).
|-
| EX || Excitation; used to locate the feedpoint on the tagged wire.
|-
| FR || Design frequency.
|-
| EN || End of deck.
|-
| CM, CE || Comments, ignored.
|}

'''Not supported''': lumped loads (LD), transmission line cards (TL) and other advanced cards are ignored. Antennas that depend on loading coils or line matching will therefore solve differently than in a full NEC package. A deck with no GW card is rejected.

== Tips ==
* Model in a dedicated NEC tool, verify the pattern and impedance there, then export and import the deck.
* Keep the geometry moderate in size; extremely finely segmented models gain nothing and solve slowly.
* If no excitation card is present the feed defaults to the center of the first wire.

[[Category:Antennas]] [[Category:SimTX]]

End-Fed Half-Wave Antenna

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Clanker: Create EFHW page

The '''end-fed half-wave''' (EFHW) is a half-wavelength wire fed at one end through a 49:1 impedance transformer (unun). It is the default antenna in SimTX, configured as a 32.5 m wire at 10 m height, which is close to resonance at the default frequency of 4625 kHz.

== Geometry in SimTX ==
A single wire hung as a catenary from the configured height, fed at one end. The 49:1 transformer is included in the electrical model. Default wire length 32.5 m.

== Characteristics ==
* Typical gain around 2.1 dBi with a takeoff angle around 28 degrees at typical heights.
* Because the end of a half-wave wire presents a very high impedance, the 49:1 transformer is required to bring it near 50 ohms. The transformer costs a small insertion loss (about half a decibel, growing when the match is poor).
* Multi-band behaviour: like all end-fed half-waves it also presents usable matches near integer multiples of its fundamental, with slightly worse match and higher transformer loss on the harmonics.
* Practically convenient: one support, feedpoint at the end.

== Sizing ==
The wire should be an electrical half-wave: roughly 143 to 150 divided by the frequency in MHz, in meters. The default 32.5 m corresponds to a fundamental near 4.6 MHz, which is why the application defaults to 4625 kHz. Operating the default antenna at a very different frequency (for example 7.1 MHz, between its harmonics) produces a severe mismatch and almost no radiated signal; either change the wire length or pick a frequency near a harmonic.

== When to use ==
As a realistic general-purpose wire antenna, especially when simulating portable or space-constrained stations. For best single-band performance a resonant [[Dipole Antenna]] at good height still has the edge.

[[Category:Antennas]]

Beverage Antenna

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Clanker: Create beverage page

The '''Beverage''' is a travelling-wave antenna: a very long, very low wire, classically used for low-band reception. It is highly directional along the wire.

== Geometry in SimTX ==
A single straight wire along the azimuth, mounted very low; the model caps the height at 3 m regardless of the height setting, which reflects how Beverages are built. Default length 80 m; a length of 0 selects two wavelengths at the operating frequency, and real Beverages are typically one to several wavelengths long.

== Characteristics ==
* Typical gain figure around 8 dBi of directivity along the wire with a very low takeoff angle around 8 degrees.
* As a travelling-wave antenna it is inherently mismatched and lossy as a transmitting antenna: expect a permanently mediocre SWR (around 2.8) and note the high default feedline loss (2 dB). Real stations use Beverages for receive, not transmit.
* Very directive front lobe toward the azimuth heading; point it at the target region.
* Works best over average to poor ground.

== When to use ==
Mostly for experimentation and for simulating receive-style directivity on the low bands. As a transmit antenna it is deliberately inefficient; a [[Vertical Antenna]] radiates far better on the same bands.

[[Category:Antennas]]

Longwire Antenna

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Clanker: Create longwire page

The '''longwire''' is a straight wire several wavelengths long, fed at one end. Unlike a random end-fed wire, a true longwire develops directivity along the wire direction.

== Geometry in SimTX ==
A single horizontal wire running along the azimuth with realistic sag, default length 21 m; a length of 0 selects two wavelengths at the operating frequency.

== Characteristics ==
* Typical gain around 4 dBi with lobes that press toward the wire direction as the wire gets electrically longer.
* Typical takeoff angle around 20 degrees.
* Multi-band by nature: it presents workable (though rarely excellent) matches on many frequencies, with SWR varying between harmonics. Expect a rougher match than a resonant dipole; a tuner-style loss is reflected in the higher default feedline loss (1.2 dB).
* Directional along the wire run: point the azimuth roughly toward the target.

== When to use ==
When simulating a simple field or shortwave-listener style station with one long wire, or when multi-band capability matters more than a clean match. For a serious single band, a resonant [[Dipole Antenna]] usually wins.

[[Category:Antennas]]

Full-Wave Loop Antenna

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Clanker: Create loop page

The '''full-wave loop''' is a closed wire loop whose circumference is one wavelength, mounted in a vertical plane and fed at the bottom.

== Geometry in SimTX ==
The loop is modelled as a vertical-plane polygon with the configured circumference (the length field is labelled '''Circumference'''). The default is 1.0 m, which is only sensible for very high frequencies; set 0 to get a full-wave circumference for the operating frequency, or enter it explicitly.

== Characteristics ==
* Typical gain around 1.5 dBi with a high takeoff angle around 55 degrees: primarily a short and medium range antenna.
* Broadside pattern (perpendicular to the loop plane), controlled by the azimuth setting, but lobes are broad.
* Distinctly '''narrowband''': the SWR is excellent at resonance and degrades quickly off frequency. Retune (adjust circumference) when changing frequency by more than a fraction of a percent.
* Quiet and clean pattern; a classic choice for regional nets.

== Sizing ==
A full-wave circumference in meters is approximately 300 divided by the frequency in MHz (see [[Antenna Calculations]]). Example: about 84 m at 3.6 MHz, about 42 m at 7.1 MHz.

== When to use ==
For reliable short and medium range ionospheric coverage on a fixed frequency. Poor choice for frequency-agile operation because of the narrow match.

[[Category:Antennas]]

Yagi Antenna

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Clanker: Create yagi page

The '''Yagi''' (Yagi-Uda) is a directional beam antenna: a driven element plus a reflector behind it and one or more directors in front. SimTX provides a '''3-element''' and a '''5-element''' version.

== Geometry in SimTX ==
Horizontal elements on a boom that points along the configured azimuth. The driven element is a split half-wave; the reflector sits behind it and the directors in front, with element lengths and spacings following conventional Yagi proportions. The driven element length defaults to 10.1 m; a value of 0 sizes the antenna for the operating frequency. Elements are modelled as aluminium-style tubing rather than thin wire.

== Characteristics ==
{| class="wikitable"
! Version !! Typical gain !! Typical takeoff angle
|-
| 3 elements || 7.5 dBi || 14°
|-
| 5 elements || 10.2 dBi || 10°
|}
* Strongly directional: most of the power goes toward the azimuth heading, with a large front-to-back advantage. Aim it at the target region; a misaimed Yagi is worse than a dipole.
* Low takeoff angles at reasonable heights make Yagis the tool of choice for long-distance work on the higher HF bands.
* Wider SWR bandwidth than simple wire antennas, the 5-element version widest.

== Practical notes ==
* Set '''Azimuth''' to the great-circle bearing toward the target area (0 is north, 90 is east).
* A full-size Yagi for the low bands is enormous (a 3.6 MHz driven element is about 40 m); realistically they are used from roughly 14 MHz upward.
* Height still matters: mount at least half a wavelength up for the advertised low-angle performance.

== When to use ==
For point-to-point and long-distance coverage toward a known direction on the higher bands. For all-around coverage use a [[Dipole Antenna]], [[Vertical Antenna]] or [[Full-Wave Loop Antenna]] instead.

[[Category:Antennas]]

Vertical Antenna

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Clanker: Create vertical page

The '''vertical''' is a quarter-wave monopole worked against ground. It is omnidirectional and radiates well at low elevation angles, which favours distance.

== Geometry in SimTX ==
A single vertical radiator fed at the base against the ground. The element length defaults to 5.1 m; a length of 0 selects a resonant quarter-wave element for the operating frequency. The azimuth field is disabled because the pattern is symmetric. The height field influences the surrounding path geometry rather than the radiator length.

== Characteristics ==
* Typical gain around 1.8 dBi, evenly in all compass directions.
* Low typical takeoff angle around 18 degrees: good for long-distance ionospheric paths despite the modest gain figure.
* Vertical polarization, which is strongly favoured on short-range ground-hugging paths. For local and regional coverage below a few hundred kilometers on the lower bands, a vertical often outperforms much "bigger" horizontal antennas.
* Ground quality matters more than for horizontal antennas; poor ground raises losses.

== Sizing ==
A resonant quarter-wave element in meters is approximately 71.5 divided by the frequency in MHz, half the dipole length (see [[Antenna Calculations]]). Example: about 10 m at 7.1 MHz.

== When to use ==
Pick the vertical for omnidirectional low-angle coverage, groundwave range on the low bands, or when there is no room for long horizontal wires. Its weakness is medium-range ionospheric coverage, where high-angle radiators (dipole, inverted-V, loop) do better.

[[Category:Antennas]]

Inverted-V Antenna

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Clanker: Create inverted-v page

The '''inverted-V''' is a variant of the [[Dipole Antenna]] supported at a single central point, with the two legs sloping down toward the ends. It needs only one mast, which makes it a common practical compromise.

== Geometry in SimTX ==
The feedpoint sits at the apex (the configured height) and the legs droop at roughly 40 degrees. The default length is 10.8 m; a length of 0 selects the resonant length for the operating frequency.

== Characteristics ==
* Typical gain around 1.8 dBi, a little below a flat dipole at the same apex height, because the average wire height is lower.
* Nearly omnidirectional; the sloping legs fill in the nulls a flat dipole has off its ends.
* Typical takeoff angle around 40 degrees: well suited to short and medium range ionospheric coverage.
* Slightly wider SWR bandwidth than a flat dipole.

== When to use ==
Choose the inverted-V when simulating a station with a single support, for regional coverage, or when an omnidirectional pattern is preferred over the dipole's broadside preference. For long-distance work a high flat dipole or a Yagi performs better.

[[Category:Antennas]]

Dipole Antenna

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Clanker: Create dipole page

The '''dipole''' is a half-wave wire antenna fed at its center. It is the classic reference antenna for HF work: simple, predictable and effective.

== Geometry in SimTX ==
Two equal wire halves run horizontally along the azimuth direction with a slight realistic sag, fed in the middle. The default wire length is 10.1 m; a length of 0 selects the resonant half-wave length for the operating frequency automatically.

== Characteristics ==
* Typical gain around 5.5 dBi over ground, broadside to the wire (peaks perpendicular to the wire run).
* Non-directional in practice: a figure-eight pattern with broad lobes and shallow nulls off the wire ends.
* Typical takeoff angle around 30 degrees at the default 10 m height. Radiation angle depends strongly on height, see below.
* Moderate bandwidth: SWR stays reasonable over several percent of the center frequency; odd multiples of the resonant frequency are also usable.

== Height ==
Height above ground is the dominant tuning knob:
* Below roughly a quarter wavelength, the dipole radiates mostly straight up. That is excellent for short-range regional coverage (a few hundred kilometers via near-vertical ionospheric reflection) and poor for long distance.
* Around half a wavelength and above, a strong low-angle lobe forms and long-distance performance improves markedly.

== Sizing ==
A practical resonant half-wave length in meters is approximately 143 divided by the frequency in MHz (see [[Antenna Calculations]]). Examples: about 40 m at 3.6 MHz, about 20 m at 7.1 MHz, about 10 m at 14.2 MHz. Leaving the length at 0 lets SimTX use the resonant length directly.

== When to use ==
A resonant dipole at a sensible height is a strong general-purpose choice on any HF band and a good baseline against which to compare other antennas.

[[Category:Antennas]]

Antenna System

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The antenna is the most influential part of a SimTX station. Each antenna is modelled as real wire geometry and solved electromagnetically at the operating frequency, producing a three-dimensional radiation pattern and a feedpoint impedance. Antenna choice therefore changes gain, directionality, takeoff angle, SWR and ultimately who can hear the transmission.

== Configuration fields ==
{| class="wikitable"
! Field !! Meaning
|-
| Type || One of the built-in antenna types below, or a custom geometry via [[NEC File Import]].
|-
| Wire Length (m) || The main dimension. Its label adapts to the type (circumference for the loop, element length for the vertical, driven element for the Yagis). '''0 means resonant at the operating frequency''': the length is derived automatically.
|-
| Height (m) || Height of the feedpoint or apex above ground. Height strongly shapes the vertical radiation pattern of horizontal antennas: low antennas radiate upward (short range), high antennas radiate at low angles (long range).
|-
| Azimuth (°) || Orientation, 0 is north, 90 is east. For directional antennas this is the pointing direction; for wire antennas it is the direction the wire runs. Disabled for the vertical.
|-
| Feedline Loss (dB) || Fixed loss of the cable between transmitter and antenna. Subtracted from the radiated signal in both cases.
|}

== Built-in antenna types ==
{| class="wikitable"
! Type !! Typical gain (dBi) !! Directional !! Typical takeoff angle !! Default length (m) !! Default feedline loss (dB) !! Page
|-
| Dipole || 5.5 || No || 30° || 10.1 || 1.0 || [[Dipole Antenna]]
|-
| Inverted-V || 1.8 || No || 40° || 10.8 || 1.0 || [[Inverted-V Antenna]]
|-
| Vertical || 1.76 || No || 18° || 5.1 || 0.5 || [[Vertical Antenna]]
|-
| Yagi 3-element || 7.5 || Yes || 14° || 10.1 || 0.8 || [[Yagi Antenna]]
|-
| Yagi 5-element || 10.2 || Yes || 10° || 10.1 || 0.8 || [[Yagi Antenna]]
|-
| Full-wave Loop || 1.5 || No || 55° || 1.0 || 0.3 || [[Full-Wave Loop Antenna]]
|-
| Longwire || 4.0 || Yes || 20° || 21.0 || 1.2 || [[Longwire Antenna]]
|-
| Beverage || 8.0 || Yes || 8° || 80.0 || 2.0 || [[Beverage Antenna]]
|-
| EFHW + 49:1 unun || 2.1 || No || 28° || 32.5 || 0.6 || [[End-Fed Half-Wave Antenna]]
|}
The gain and takeoff figures are typical labels; the actual values come from the full geometry solve and vary with frequency, length, height and azimuth.

== How the antenna affects the link ==
For every propagation path the simulation reads the antenna's realized gain in the exact direction and elevation of that path, then subtracts feedline loss, mismatch loss (from SWR), transformer loss (end-fed only) and any protection foldback. Both the transmitting and the receiving antenna contribute in this way. Consequences:

* '''Takeoff angle matters as much as gain.''' Long-distance ionospheric paths leave at low elevation angles; short-range paths need high-angle radiation. An antenna with modest gain at the right angle beats a high-gain antenna pointed at the wrong angle. See [[Propagation Basics]].
* '''Directional antennas must be aimed.''' A 5-element Yagi pointed away from the receiver can be worse than a dipole.
* '''Polarization matters.''' Ground-hugging short-range propagation strongly favours vertical polarization; horizontal antennas radiate very little at grazing angles. On ionospheric paths polarization is scrambled and costs a fixed few decibels regardless of antenna.
* '''Height shapes the pattern.''' Raising a horizontal antenna lowers its main lobe. As a rule of thumb, half a wavelength of height gives a useful low-angle lobe.

== Local estimate ==
The Radio Deck shows the solved peak gain (dBi) and the VSWR at 50 ohms for the current configuration before any session starts, recomputed whenever frequency, power or antenna fields change. Use it to sanity-check a design before transmitting.

== See also ==
* [[Antenna Calculations]]
* [[NEC File Import]]
* [[SWR and Transmitter Protection]]

[[Category:SimTX]] [[Category:Antennas]]

SWR and Transmitter Protection

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Clanker: Create SWR page

The standing wave ratio (SWR) describes how well the antenna system is matched to the transmitter's 50 ohm output. It is shown live on the '''SWR''' meter of the Radio Deck, together with forward ('''FWD''') and reflected ('''REF''') power.

== What SWR means ==
* '''SWR 1.0''' is a perfect match: all forward power reaches the antenna.
* '''SWR 2.0''' reflects about 11 percent of the power (about 0.5 dB loss).
* '''SWR 3.0''' reflects 25 percent (about 1.25 dB loss).
* Very high SWR means the antenna barely accepts power at the operating frequency.
See [[Antenna Calculations]] for the arithmetic.

== Where mismatch comes from ==
In SimTX the antenna is solved as physical wire geometry at the operating frequency, so SWR behaves as it does in reality:
* Operating far from the antenna's resonant frequency raises SWR quickly. A wire length of 0 in the antenna form means "resonant at the operating frequency" and gives a good match on that frequency.
* Antenna height, ground and geometry shift the feedpoint impedance.
* Narrowband antennas (notably the full-wave loop) show a good match only over a small frequency range.
* End-fed antennas are matched through a 49:1 transformer, which adds a small loss of its own, see [[End-Fed Half-Wave Antenna]].

== Transmitter protection ==
Like a real transceiver, the simulated transmitter folds back output power into a bad match to protect its finals:
* Protection begins at about '''SWR 2.5'''.
* Above that, output power is reduced progressively; a severe mismatch can cost several decibels on top of the mismatch loss itself.
The result is visible as reduced FWD power and reduced signal at receivers.

== Practical advice ==
* After changing frequency, check the SWR meter before a long transmission. The deck shows a local estimate even before the session starts.
* Match the antenna to the band: set the wire length near resonance (or leave it at 0 for automatic resonant length), see [[Antenna Calculations]].
* A modest SWR up to about 2 is normal and costs little. Chasing a perfect 1.0 is rarely worth it.

[[Category:SimTX]]

Power Amplifier Behaviour

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The simulated power amplifier (PA) heats up under load, reduces power to protect itself and can suffer permanent damage when abused. Its state is visible on the '''TEMP''' meter of the Radio Deck and in the deck header.

== Heating ==
Transmitting dissipates heat in the amplifier finals. The temperature shown on the TEMP meter starts at room temperature (about 24 °C) and rises with output power, duty cycle and drive level. Constant-envelope modes (FM, CW key-down, steady tones) heat the amplifier considerably faster than speech on SSB, which has a low average power. When transmission stops the amplifier cools back down over time.

== Thermal foldback ==
When the finals get hot the amplifier automatically reduces output power:
* Foldback begins at roughly '''78 °C''' and the deck header shows a thermal foldback notice.
* It becomes aggressive above roughly '''92 °C'''; forward power visibly sags.
* The header shows '''PA OVERHEATED''' while the amplifier is in thermal distress.
Foldback is protective and reversible: power returns as the amplifier cools.

== Permanent damage ==
Sustained operation above roughly '''110 °C''' starts to damage the finals. Damage:
* accumulates faster the hotter the amplifier runs (minutes just above the threshold, seconds at extreme temperatures),
* is permanent for the session; cooked finals do not heal on cooldown,
* permanently reduces the achievable output power and adds distortion and slow drift to the signal.

== Operating guidance ==
* Watch the TEMP meter during long transmissions, especially FM, AM and digital modes at full power.
* If the temperature approaches 78 °C, reduce power, shorten transmissions or pause between overs.
* High final drive and low PA headroom (see [[Advanced Transmitter Settings]] and [[Radio Presets]]) increase dissipation at the same output power.
* A badly matched antenna also stresses the transmitter; the protection circuit reduces power at high SWR, see [[SWR and Transmitter Protection]].

[[Category:SimTX]]

Advanced Transmitter Settings

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The advanced settings panel ('''Show advanced transmitter settings''' in the RF Signal section) exposes fifteen parameters that define the transmitter's imperfections. [[Radio Presets]] fill all of them at once; manual edits are possible afterwards.

{| class="wikitable"
! Setting !! Default !! Range !! Effect
|-
| Final drive (dB) || 0.0 || -40 to 40 || Extra drive into the power amplifier. Positive values push the amplifier toward compression and distortion.
|-
| PA headroom (dB) || 12.0 || 0.1 to 40 || How far below amplifier saturation the nominal signal sits. Small headroom means the signal clips early.
|-
| Compressor (dB) || 1.5 || 0 to 30 || Audio compression before modulation. Raises average loudness at the cost of naturalness.
|-
| PA softness || 2.8 || 0.5 to 10 || Shape of the amplifier limiting curve. Low values clip abruptly (harsh distortion), high values limit gently.
|-
| AM/PM (deg) || 6.0 || 0 to 45 || Phase shift that accompanies amplitude compression. Adds splatter and roughness when the amplifier is driven hard.
|-
| Carrier leak (dB) || 60.0 || 0 to 120 || Suppression of the residual carrier in suppressed-carrier modes. Higher is cleaner.
|-
| Sideband sup. (dB) || 60.0 || 0 to 120 || Suppression of the unwanted sideband in SSB. Higher is cleaner.
|-
| Freq error (Hz) || 0.0 || -10000 to 10000 || Static frequency offset of the transmitter oscillator.
|-
| Hum level (dB) || 120.0 || 0 to 120 || Mains hum suppression; 120 means no audible hum. Lower values add hum at the hum frequency.
|-
| Hum freq (Hz) || 0.0 || 0 to 400 || Mains hum fundamental (typically 50 or 100, or 60 or 120). Zero disables.
|-
| AM index || 0.85 || 0 to 1.2 || AM modulation depth. Above 1.0 is overmodulation with distortion and splatter.
|-
| PA sag (dB) || 0.0 || 0 to 30 || Supply voltage sag under load; produces a power dip on voice peaks and key-down.
|-
| TX noise (dB) || 120.0 || 0 to 160 || Broadband transmitted noise floor suppression. Higher is cleaner.
|-
| Phase noise (dB) || 120.0 || 0 to 160 || Oscillator phase noise suppression. Higher is cleaner; low values smear the signal spectrally.
|-
| CW rise (ms) || 5.0 || 0 to 50 || CW keying envelope rise time. Very short values cause key clicks.
|}

Other bounds: frequency must be positive, power must be at least 0 W, and the duty cycle used by the amplifier model runs from 0 to 1 with a default of 0.5.

The suppression-style values (carrier leak, sideband suppression, hum level, TX noise, phase noise) are expressed as decibels below the wanted signal, so larger numbers always mean a cleaner transmitter.

[[Category:SimTX]]

Radio Presets

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A radio preset gives the transmitter the character of a class of real equipment: how clean the signal is, how much power is available, how hard the amplifier compresses, how much hum and phase noise are present. Selecting a preset overwrites the power field and all [[Advanced Transmitter Settings]]; individual values can be edited afterwards.

Presets are simulation starting points that represent classes of equipment, not measured laboratory profiles of specific radios.

== Preset list ==
{| class="wikitable"
! Preset !! Power (W) !! Character
|-
| Generic HF transceiver || 100 || Neutral modern transceiver, the default starting point.
|-
| Clean lab exciter || 10 || Near-ideal signal source: no compression, very low noise, excellent carrier and sideband suppression. Useful as a reference.
|-
| Icom IC-7300 class HF rig || 100 || Clean modern SDR-based 100 W transceiver.
|-
| Icom IC-705 class QRP SDR || 10 || Clean low-power portable SDR.
|-
| Icom IC-7610 class base SDR || 100 || High-end base station, very clean output.
|-
| Yaesu FTDX10 class HF SDR || 100 || Modern hybrid SDR transceiver.
|-
| Elecraft KX2/KX3 class QRP || 10 || High-quality low-power portable.
|-
| Yaesu FT-817/818 class QRP || 5 || Older portable design: modest headroom, more compression and hum.
|-
| Kenwood TS-590 class HF rig || 100 || Clean conventional 100 W transceiver.
|-
| Xiegu G90 class portable HF || 20 || Budget portable: audible compression and a rougher signal.
|-
| (tr)uSDX / uSDX QRP Class-E || 5 || Minimalist kit radio: heavy compression, significant distortion and drift artifacts.
|-
| Rugged HF manpack || 20 || Military-style manpack: robust but not clean.
|-
| Vintage tube SSB || 100 || Tube-era transmitter: soft compression, hum, slow keying.
|-
| Collins KWM-2 class tube SSB || 100 || Classic tube SSB station.
|-
| Vintage AM boatanchor || 50 || Full-carrier AM transmitter with strong hum and character. High modulation index.
|-
| Overdriven export AM/SSB || 25 || Deliberately dirty CB-style export radio: overmodulation, splatter, poor suppression.
|-
| Budget VHF/UHF handheld FM || 5 || Inexpensive FM handheld.
|-
| Homebrew Class-E AM || 10 || Home-built high-efficiency AM rig, full modulation.
|-
| Overdriven driver / poor ALC || 25 || Worst-case example: extreme drive, minimal headroom, heavy distortion and noise.
|}

== Choosing a preset ==
* For intelligibility tests and clean comparisons, use '''Clean lab exciter'''.
* For realistic amateur operation, pick a preset in the class of radio being simulated; the 100 W transceiver presets behave similarly with small differences in compression and noise.
* The dirty presets ('''Overdriven export AM/SSB''', '''Overdriven driver / poor ALC''', '''(tr)uSDX''') are useful for practising recognition of poor signals on a receiver.

Low-headroom, high-drive presets heat the amplifier faster at a given power, see [[Power Amplifier Behaviour]].

[[Category:SimTX]]

Sessions and Queueing

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Every transmission is a session between the transmitter client and the server. The server decides whether a new session is admitted immediately, queued or rejected.

== Session lifecycle ==
A session created with '''Start TX''' passes through these states:
* '''Starting''': the client is contacting the server.
* '''Queued''': the server is full for now; the list shows how many sessions are ahead. The session starts automatically when a slot frees up.
* '''Running''': the transmission is on the air and telemetry updates the Radio Deck.
* '''Stopping / Stopped''': the operator ended the session.
* '''Finished''': the source completed (for example the audio file ended).
* '''Failed''': the server rejected the session; the reason is shown.
* '''Kicked''': the server operator ended the session remotely; a dialog shows the reason.

== Server limits ==
Servers can limit the total number of sessions, the number of transmit sessions, and the number of sessions per user. The user bucket is the callsign (case-insensitive) or, depending on server policy, the client address. When a transmit limit is reached new sessions are queued in order; when a policy forbids the session outright it is rejected with a reason.

== Multiple sessions ==
The client can run several sessions at once (subject to server limits). The '''Active Sessions''' list shows each with its own state, and '''Stop Selected''' / '''Stop All''' control them individually or together.

== Disconnects ==
If the control connection drops, the client reconnects automatically every 3 seconds. Sessions that were kicked or rejected show the server-supplied reason; an empty reason is displayed as "No reason given".

[[Category:SimTX]]

Station Configuration

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Clanker: Create station configuration page

The station identity consists of a callsign, a geographic location and an antenna. Together with the transmitter settings it fully describes the simulated station.

== Callsign ==
A free-form station identifier (default PA3NL). It is shown to the server, in session lists and to other users. Servers may apply per-user session limits keyed by callsign, see [[Sessions and Queueing]]. The callsign is persisted between application runs.

== Location ==
Latitude and longitude, set by clicking the world map or typing into the '''Lat''' and '''Lon''' fields (defaults 52.3676 north, 4.9041 east). Location matters:
* It sets the distance and bearing to every receiver, which drives path loss and antenna directionality.
* It determines local time of day at the station, which affects ionospheric propagation, see [[Propagation Basics]].
* Latitude influences ionospheric behaviour; high-latitude paths are less stable.
The location is persisted between application runs.

== Antenna ==
See [[Antenna System]] for the antenna configuration fields and the list of available antenna types.

== Station presets ==
'''Save Preset...''' writes the complete configuration to a <code>.stxpreset</code> file: every form field, the radio preset choice, modulation, bandwidth mode, source type and file, microphone selection, antenna type and any imported NEC deck. '''Load Preset...''' restores it. These files are ordinary text property files and can be shared between users.

This is a different concept from the built-in [[Radio Presets]], which only describe the transmitter hardware character.

[[Category:SimTX]]

Transmission Sources

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The transmission source determines what audio or signal the transmitter sends. It is selected in the '''Transmission Source''' section of the [[Transmitter Interface]].

== Source types ==
{| class="wikitable"
! Source !! Description
|-
| Audio File || Plays an audio file. Supported formats: wav, mp3, aiff, aif, au. Files are resampled to 48 kHz. Files can be selected with '''Choose...''' or dragged onto the window.
|-
| Microphone || Transmits live audio from a selected input device. The device list appears when this source is chosen. Availability depends on the operating system audio setup.
|-
| White Noise || Generates broadband noise. Useful for testing receivers and observing the occupied bandwidth.
|-
| PipeWire || Streams the system audio (mono) on Linux systems with PipeWire. Only shown when PipeWire is available.
|-
| PipeWire Stereo || Streams system audio in stereo, intended for WFM broadcasting. Selecting it forces the WFM mode. Only shown when PipeWire is available.
|-
| GNU Radio IQ || Receives complex IQ samples from GNU Radio over a local TCP connection. The Tone field becomes '''IQ Port''' (suggested port 7355). Point a GNU Radio TCP sink at 127.0.0.1 on that port. The source sample rate equals the requested bandwidth. Selecting it forces the IQ mode.
|}

== Audio gain ==
The '''Audio Gain''' field (default 0.9) scales the source level before modulation. Driving it high increases loudness but pushes the transmitter into compression and distortion, especially with presets that have little headroom, see [[Radio Presets]].

[[Category:SimTX]]

Modulation Modes

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Clanker: Create modulation modes page

The SimTX Transmitter supports the following modulation modes. The '''Auto''' bandwidth option fills the typical bandwidth for the selected mode; the bandwidth field accepts any value down to the mode's minimum.

{| class="wikitable"
! Mode !! Full name !! Typical bandwidth !! Minimum bandwidth !! Audio range !! Type
|-
| AM (full carrier) || Amplitude modulation, double sideband, full carrier || 10 kHz || 160 Hz || 80 to 4500 Hz || Analog
|-
| AM (suppressed carrier) || Double sideband, suppressed carrier || 6 kHz || 160 Hz || 100 to 2800 Hz || Analog
|-
| USB || Upper sideband || 2700 Hz || 300 Hz || 350 to 2700 Hz || Analog
|-
| LSB || Lower sideband || 2700 Hz || 300 Hz || 350 to 2700 Hz || Analog
|-
| CW || Continuous wave (Morse keying) || 150 Hz || 50 Hz || n/a || Analog
|-
| NFM || Narrowband FM || 12.5 kHz || 2.5 kHz || 200 to 3000 Hz || Analog
|-
| WFM || Wideband FM (broadcast) || 180 kHz || 50 kHz || 30 Hz to 15 kHz || Analog
|-
| IQ || External complex IQ input || 48 kHz || 100 Hz || n/a || Passthrough
|-
| WSPR || Weak Signal Propagation Reporter || 6 Hz || 6 Hz || n/a || Digital
|-
| FT8 || Franke-Taylor FT8 || 50 Hz || 50 Hz || n/a || Digital
|}

== Mode notes ==
* '''USB and LSB''' are suppressed-carrier modes. The carrier leak and opposite-sideband suppression settings in [[Advanced Transmitter Settings]] control how imperfect the suppression is. By convention LSB is used below 10 MHz and USB above, but SimTX does not enforce this.
* '''AM''' modes expose the AM modulation index setting. An index above 1.0 is overmodulation and produces audible distortion and splatter.
* '''CW''' exposes the key rise time setting. Very short rise times produce key clicks that widen the occupied bandwidth.
* '''NFM and WFM''' are constant-envelope modes; they are less affected by amplifier compression but need considerably more signal at the receiver than SSB. WFM supports stereo when fed from the PipeWire Stereo source.
* '''IQ''' passes externally generated complex baseband (for example from GNU Radio) straight to the channel. Selecting the GNU Radio IQ source forces this mode.
* '''WSPR and FT8''' are extremely narrow digital modes that remain decodable far below the noise floor, which makes them useful for testing marginal propagation paths, see [[Propagation Basics]].

== Field interactions ==
* The low-cut field is editable for USB, LSB, both AM modes, NFM and WFM.
* Opposite-sideband suppression applies to USB and LSB only.
* Carrier leak applies to USB, LSB and suppressed-carrier AM.
* AM index applies to the two AM modes.
* CW rise time applies to CW only.
* PipeWire Stereo forces WFM; GNU Radio IQ forces IQ.

[[Category:SimTX]]

Transmitter Interface

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Clanker: Create interface reference

This page is a reference for the SimTX Transmitter application window. The window is split into a configuration form on the left and a live monitoring area on the right, with a status bar at the bottom.

== Server selector ==
Shown at startup and after a disconnect. It lists known servers with their details and provides:
* '''Add Server...''': name, host, port (1 to 65535, default 5100), optional description.
* '''Connect''': establishes the control connection and opens the main window.

If the connection to the server drops while the application is running, the title area indicates that the client is reconnecting and retries every 3 seconds.

== Station section ==
* '''Server''' row with a '''Disconnect''' button (returns to the server selector).
* '''Callsign''': station identifier shown to the server and other users. Persisted between runs.
* '''Location''': a clickable world map that fills the '''Lat''' and '''Lon''' fields. Coordinates can also be typed directly. Persisted between runs.

== RF Signal section ==
* '''Frequency (Hz)''': carrier frequency. Default 4625000 (4625 kHz), chosen to match the default antenna, see [[Getting Started]].
* '''Power (W)''': requested transmitter output power. Default 100.
* '''Radio Preset''': selects a transmitter character, see [[Radio Presets]]. Selecting a preset overwrites the power field and all advanced settings.
* '''Modulation''': the modulation mode, see [[Modulation Modes]].
* '''Bandwidth (Hz)''' with an '''Auto''' checkbox. Auto fills the typical bandwidth of the selected mode. Default 2700.
* '''Low-cut (Hz)''': audio low-frequency cutoff. Default 350. Editable only for modes where it applies.
* '''Show advanced transmitter settings''': expands the fifteen fine-tuning fields, see [[Advanced Transmitter Settings]].

== Transmission Source section ==
* '''Source Type''': see [[Transmission Sources]].
* '''Audio Gain''': input level, default 0.9.
* '''Microphone''': device selector, visible only for the Microphone source.
* '''Tone (Hz)''': test tone frequency, default 1000. For the GNU Radio IQ source this field is relabelled '''IQ Port'''.
* '''Audio File''' row with '''Choose...'''. Audio files can also be dragged onto the window (wav, mp3, aiff, aif, au).
A hint line below the controls describes the currently selected source.

== Antenna section ==
* '''Type''': antenna selector, default EFHW + 49:1 unun. See [[Antenna System]].
* '''Wire Length (m)''': main dimension of the antenna. The label adapts to the type (Circumference for the loop, Element Length for the vertical, Driven Element for the Yagis). A value of 0 means resonant length at the operating frequency.
* '''Height (m)''': feedpoint or apex height above ground. Default 10.
* '''Azimuth (°)''': orientation, 0 is north. Disabled for the vertical, which is omnidirectional.
* '''Feedline Loss (dB)''': fixed loss between transmitter and antenna.
* '''Import NEC...''' and '''Use built-in''': load or clear a custom antenna geometry, see [[NEC File Import]].

== Start row ==
* '''Start TX''': starts a transmission session with the current configuration.
* '''Save Preset...''' and '''Load Preset...''': store or restore the complete station configuration as a <code>.stxpreset</code> file. This includes every field, the source selection and any imported NEC deck.

== Radio Deck ==
The right-hand panel shows six meters:
{| class="wikitable"
! Meter !! Unit !! Meaning
|-
| FWD || W || Forward output power
|-
| REF || W || Reflected power returning from the antenna
|-
| SWR || :1 || Standing wave ratio at the transmitter
|-
| ALC || dB || Automatic level control action
|-
| TEMP || °C || Power amplifier finals temperature
|-
| BUF || s || Audio buffer fill
|}
Before the server reports measurements the deck shows a local estimate computed from the antenna configuration. Once telemetry arrives the header switches to measured output. If the amplifier overheats the header shows a PA OVERHEATED warning, see [[Power Amplifier Behaviour]].

== Active Sessions ==
A list of the operator's sessions with id, callsign, frequency, modulation, power, status, source, SWR, bandwidth and server address. Buttons: '''Stop Selected''', '''Stop All''', '''Clear Finished'''. Session states are described in [[Sessions and Queueing]].

[[Category:SimTX]]

Getting Started

2026-07-05T08:41:40Z

Clanker: Create getting started guide

This page describes how to launch the SimTX Transmitter, connect to a server and make a first transmission.

== Requirements ==
* Java runtime (the transmitter is a Java desktop application).
* Network access to a SimTX server. The default server port is '''5100'''.
* Optionally: audio files (wav, mp3, aiff, aif, au), a microphone, PipeWire (Linux system audio) or GNU Radio for IQ input.

== Connecting to a server ==
When the application starts, a server selector dialog is shown before the main window.

# Select a server from the list, or press '''Add Server...''' and enter a name, host, port (1 to 65535, default 5100) and an optional description.
# Press '''Connect'''. The main window opens once the control connection is established.

If the control connection drops later, the client shows a reconnecting notice and retries every 3 seconds. The '''Disconnect''' button returns to the server selector.

== First transmission ==
The default configuration is chosen to work immediately:

* Frequency '''4625 kHz''', power '''100 W''', modulation preselected with a '''2700 Hz''' bandwidth.
* Antenna: '''End-fed half-wave (EFHW) with 49:1 transformer''', 32.5 m wire at 10 m height. This antenna is close to resonance at 4625 kHz, which is why that frequency is the default. Changing the frequency far from resonance without changing the antenna produces a severe mismatch and very little radiated signal.

Steps:

# Set a callsign in the '''Station''' section (default PA3NL) and click the world map to place the station, or type latitude and longitude directly.
# In '''Transmission Source''', keep the source type '''Audio File''' and press '''Choose...''' to select a file, or drag an audio file onto the window. Supported formats: wav, mp3, aiff, aif, au.
# Press '''Start TX'''.
# Watch the '''Radio Deck''' on the right. Before the server reports data it shows a local estimate; once telemetry arrives the header changes to measured output. The session also appears in the '''Active Sessions''' list.

If the server is full the session is queued and the list shows the queue position, see [[Sessions and Queueing]].

== Stopping ==
Select the session in '''Active Sessions''' and press '''Stop Selected''', or press '''Stop All'''. '''Clear Finished''' removes completed entries from the list.

== Saving the setup ==
'''Save Preset...''' stores the complete station configuration (all fields, source, antenna, including an imported NEC deck) in a <code>.stxpreset</code> file that '''Load Preset...''' restores later. This is distinct from the built-in [[Radio Presets]], which only set the transmitter character.

== Next steps ==
* Learn the full interface: [[Transmitter Interface]]
* Choose a better antenna for the target band: [[Antenna System]]
* Understand mismatch warnings: [[SWR and Transmitter Protection]]

[[Category:SimTX]]

SimTX Transmitter

2026-07-05T08:41:20Z

Clanker: Create transmitter overview page

'''SimTX Transmitter''' is the operator client of the SimTX radio simulation platform. It lets a user configure a virtual radio station (callsign, location, transmitter, antenna) and transmit audio or data signals into a shared simulated radio spectrum hosted by a SimTX server. Receivers connected to the same server can tune to the transmission and hear it, subject to simulated antenna performance, propagation conditions and noise.

The transmitter does not emit real radio frequency energy. All modulation, amplifier behaviour and propagation are computed by the server; the client sends the station configuration and the source audio, and displays live measurements sent back by the server.

== Overview ==
A transmitter session works as follows:

# The operator starts the application and connects to a SimTX server (default port 5100).
# The station is configured: callsign, geographic location, frequency, power, modulation, transmission source and antenna.
# The operator presses '''Start TX'''. The server admits, queues or rejects the session depending on its session limits.
# While the session runs, the Radio Deck shows live measured values: forward and reflected power, SWR, ALC, amplifier temperature and audio buffer level.
# The session ends when the source finishes, the operator stops it, or the server ends it.

== Main topics ==
* [[Getting Started]]: installation, connecting to a server, first transmission
* [[Transmitter Interface]]: reference for every control in the application window
* [[Modulation Modes]]: supported modes and their bandwidths
* [[Transmission Sources]]: audio files, microphone, white noise, PipeWire, GNU Radio IQ
* [[Radio Presets]]: built-in transmitter characteristics, from clean lab exciters to overdriven CB rigs
* [[Advanced Transmitter Settings]]: the fifteen fine-tuning parameters
* [[Station Configuration]]: callsign, location and saving station presets
* [[Antenna System]]: how antennas are modelled and configured, with a page per antenna type
* [[Antenna Calculations]]: resonant lengths, SWR, gain and loss arithmetic
* [[SWR and Transmitter Protection]]: what happens when the antenna is mismatched
* [[Power Amplifier Behaviour]]: heating, power foldback and permanent damage
* [[Sessions and Queueing]]: admission, queue positions, rejections and kicks
* [[Propagation Basics]]: what determines whether a signal is heard at a distance

== What SimTX simulates ==
From the operator's point of view the simulation covers:
* Transmitter imperfections: compression, distortion, carrier leakage, hum, phase noise and more, selectable through [[Radio Presets]] or tuned individually.
* A physical antenna model: each antenna is solved as real wire geometry at the operating frequency, producing a radiation pattern, feedpoint impedance and SWR. Custom antennas can be imported as NEC decks, see [[NEC File Import]].
* Amplifier thermodynamics: sustained transmission heats the finals, reduces output power and can permanently damage the amplifier, see [[Power Amplifier Behaviour]].
* Radio propagation between stations, including ionospheric effects, time of day and distance, see [[Propagation Basics]].

[[Category:SimTX]]