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{{Documentation navigation}}
{{Documentation navigation}}


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.
The antenna sets a station's gain, direction, takeoff angle and SWR, and with them who can hear the transmission.


== Choose and tune an antenna ==
Antennas are part of a station. Add and edit them in the station editor: in the '''Stations''' tab, select the station and press '''Edit''', then go to '''Antennas'''. See [[SimTX Guide/Stations#Antennas|Stations]].


== Choose and tune an antenna ==
For a first setup, use the [[Getting Started|31 m dipole example]]. For other frequencies:
For a first setup, use the [[Getting Started|31 m dipole example]]. For other frequencies:


# Set the operating frequency first.
# Set the operating frequency first.
# Select an antenna for the intended coverage. A dipole is a useful general comparison; a vertical favors low angles; a Yagi concentrates coverage in one direction.
# Select an antenna for the intended coverage. A dipole is a good general choice, a vertical favours low angles and a Yagi beams in one direction.
# Set its main dimension for the new frequency, then check the local SWR estimate. For a dipole, <code>143 / frequency in MHz</code> metres is a starting length, not an exact solver result.
# Set its main dimension for the new frequency, then check the SWR with '''Check SWR at''' on the antenna card. For a dipole, start at <code>143 / frequency in MHz</code> metres.
# Adjust length in small steps if needed. Recheck after changing height or antenna type.
# Adjust length in small steps if needed. Recheck after changing height or antenna type.
# For a directional antenna, set Azimuth toward the intended receiving area.
# For a directional antenna on a '''Fixed''' mount, set '''Points toward''' to the intended receiving area. On a rotator mount, turn it while you transmit; see [[SimTX Guide/Rotators and tracking|Rotators and tracking]].
 
'''Length zero is a template shortcut, not an automatic tuner.''' In the current geometry solver it selects a nominal half wavelength for dipoles and inverted-Vs, a quarter wavelength for verticals, about 0.476 wavelengths for a Yagi driven element, one wavelength for a loop, and two wavelengths for longwires and Beverages. The EFHW template uses 32.5 m when zero is entered. Actual SWR still depends on the solved geometry and ground.


An antenna with a good SWR can still be weak at a distant receiver if it radiates in the wrong direction or the path is closed. See [[Propagation Basics]].
An antenna with a good SWR can still be weak at a distant receiver if it radiates in the wrong direction or the path is closed. See [[Propagation Basics]].
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| Type || One of the built-in antenna types below, or a custom geometry via [[NEC File Import]].
| 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 selects the nominal template length'''; see the type-specific rules above. It does not guarantee a resonant impedance or low SWR.
| Length (m) || The main dimension, above 0 m. Its label depends on the type: circumference for the loop, element length for the vertical, driven element for the Yagis.
|-
| Height (m) || Height of the feedpoint or apex above the 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).
|-
|-
| 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).
| Feedline loss (dB) || Loss of the cable between the radio and the antenna, on transmit and on receive.
|-
|-
| 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.
| Mount || '''Fixed''', '''Azimuth rotator''' or '''Az-El rotator'''. See [[SimTX Guide/Rotators and tracking|Rotators and tracking]].
|-
|-
| Feedline Loss (dB) || Fixed loss of the cable between transmitter and antenna. Subtracted from the radiated signal in both cases.
| Points toward (°) || On a '''Fixed''' mount, the direction of a directional antenna: 0° is north, 90° is east.
|-
| Parks at azimuth, Elevation (°) || On a rotator mount: where the antenna points when a session starts.
|}
|}


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| Vertical || 1.76 || No || 18° || 5.1 || 0.5 || [[Vertical 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 3-el || 7.5 || Yes || 14° || 10.1 || 0.8 || [[Yagi Antenna]]
|-
|-
| Yagi 5-element || 10.2 || Yes || 10° || 10.1 || 0.8 || [[Yagi Antenna]]
| Yagi 5-el || 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]]
| 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]]
| Longwire || 4.0 || Yes || 20° || 21.0 || 1.2 || [[Longwire Antenna]]
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| Beverage || 8.0 || Yes || 8° || 80.0 || 2.0 || [[Beverage 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]]
| EFHW 49:1 || 2.1 || No || 28° || 32.5 || 0.6 || [[End-Fed Half-Wave Antenna]]
|}
|}
The gain and takeoff figures are nominal type-reference values, not predictions for every setup. The current app solves the actual wire geometry; performance varies with frequency, length, height, azimuth, and ground. The Directional column distinguishes beam-like types, not whether every other antenna is equal in all directions.
Gain and takeoff angle are typical values. The real figures depend on frequency, length, height, direction and ground.
 
'''Monopole''', '''Turnstile''', '''Crossed Yagi''' and '''Helix''' are for satellite links. On a ground station, a crossed Yagi or helix starts on an '''Az-El rotator''' to follow passes. See [[SimTX Guide/Satellites|Satellites]] and [[SimTX Guide/Rotators and tracking|Rotators and tracking]].


== How the antenna affects the link ==
== How the antenna affects the link ==
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* '''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.
* '''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 ==
== Check the SWR ==
The Radio Deck shows an SWR and power estimate 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.
* In the station editor, '''Check SWR at''' on the antenna card shows the SWR at a frequency you choose.
* In the '''Transmit''' tab, the '''Station''' section shows the SWR around your transmit frequency.


== See also ==
== See also ==

Latest revision as of 20:06, 24 October 2026

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The antenna sets a station's gain, direction, takeoff angle and SWR, and with them who can hear the transmission.

Choose and tune an antenna[edit | edit source]

Antennas are part of a station. Add and edit them in the station editor: in the Stations tab, select the station and press Edit, then go to Antennas. See Stations.

For a first setup, use the 31 m dipole example. For other frequencies:

  1. Set the operating frequency first.
  2. Select an antenna for the intended coverage. A dipole is a good general choice, a vertical favours low angles and a Yagi beams in one direction.
  3. Set its main dimension for the new frequency, then check the SWR with Check SWR at on the antenna card. For a dipole, start at 143 / frequency in MHz metres.
  4. Adjust length in small steps if needed. Recheck after changing height or antenna type.
  5. For a directional antenna on a Fixed mount, set Points toward to the intended receiving area. On a rotator mount, turn it while you transmit; see Rotators and tracking.

An antenna with a good SWR can still be weak at a distant receiver if it radiates in the wrong direction or the path is closed. See Propagation Basics.

Configuration fields[edit | edit source]

Field Meaning
Type One of the built-in antenna types below, or a custom geometry via NEC File Import.
Length (m) The main dimension, above 0 m. Its label depends on the type: circumference for the loop, element length for the vertical, driven element for the Yagis.
Height (m) Height of the feedpoint or apex above the 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).
Feedline loss (dB) Loss of the cable between the radio and the antenna, on transmit and on receive.
Mount Fixed, Azimuth rotator or Az-El rotator. See Rotators and tracking.
Points toward (°) On a Fixed mount, the direction of a directional antenna: 0° is north, 90° is east.
Parks at azimuth, Elevation (°) On a rotator mount: where the antenna points when a session starts.

Built-in antenna types[edit | edit source]

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-el 7.5 Yes 14° 10.1 0.8 Yagi Antenna
Yagi 5-el 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 2.1 No 28° 32.5 0.6 End-Fed Half-Wave Antenna

Gain and takeoff angle are typical values. The real figures depend on frequency, length, height, direction and ground.

Monopole, Turnstile, Crossed Yagi and Helix are for satellite links. On a ground station, a crossed Yagi or helix starts on an Az-El rotator to follow passes. See Satellites and Rotators and tracking.

How the antenna affects the link[edit | edit source]

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.

Check the SWR[edit | edit source]

  • In the station editor, Check SWR at on the antenna card shows the SWR at a frequency you choose.
  • In the Transmit tab, the Station section shows the SWR around your transmit frequency.

See also[edit | edit source]

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