Aeronautical Mobile and Fixed Service Radio Equipment and Operation
This domain covers the equipment in an aeronautical station and how it is operated: VHF and HF transceivers, remote control, guard receivers, SELCAL, data link and the checks that prove the chain is serviceable before you trust it with a clearance.
VHF
- Band 118.000 to 136.975 MHz, amplitude modulation, 25 kHz or 8.33 kHz channel spacing. Coverage is line of sight; site, antenna height and feeder loss set usable range.
- Guard receivers monitor 121.5 MHz (civil) and 243.0 MHz (military) for distress.
HF
- 2 to 30 MHz, single sideband suppressed carrier for voice. SELCAL lets a crew be called without a continuous listening watch on a noisy channel.
- Coverage depends on frequency selection and time of day; a station normally holds several frequencies for the same area.
Operating discipline
- Remotely controlled stations use landlines or fibre to the transmitter and receiver sites; a link failure can look like a radio failure, so test the whole chain.
- Before a shift, check transmitter output, receiver sensitivity, standby power and the guard receiver. Make test transmissions only on a designated test frequency or with a brief identified call.
- Keep an off-air monitor or second receiver so you can hear your own transmission and detect distortion or a stuck carrier.
Worked example. At 09:00 local an aircraft 2 000 nm away is not heard on 5.6 MHz but is loud on 11.3 MHz. Daytime ionisation supports a higher MUF, while the lower band suffers D-layer absorption and noise. Select the higher frequency family and continue SELCAL checks.
Traps. Using AM on an HF voice channel instead of J3E; assuming a night channel will work at noon; leaving the 121.5 guard receiver muted; making a long test call on an active ATC frequency.