Editing Antenna System

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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 ==
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]].

For a first setup, use the [[Getting Started|31 m dipole example]]. For other frequencies:

# Set the operating frequency first.
# 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 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.
# 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]].

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 ==
{| class="wikitable"
! 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 [[SimTX Guide/Rotators and tracking|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 ==
{| 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-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 [[SimTX Guide/Satellites|Satellites]] and [[SimTX Guide/Rotators and tracking|Rotators and tracking]].

== 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.

== Check the SWR ==
* 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 ==
* [[Antenna Calculations]]
* [[NEC File Import]]
* [[SWR and Transmitter Protection]]

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