Radio telephony and communications equipment
Radio telephony and communications equipment
The exam checks frequency bands, equipment operation, standard phraseology and emergency procedures - the practical detail that prevents a frequency or readback error.
Core rules
- VHF airband is 118.000–136.975 MHz; 8.33 kHz channel spacing is standard in high-density airspace. VHF is line-of-sight; range increases with antenna height.
- The transceiver needs the correct frequency, volume, squelch and PTT; the audio panel selects speaker/headset and isolates radios.
- Transponder: Mode A identity, Mode C pressure altitude; squawk 7700 emergency, 7600 radio failure, 7500 unlawful interference.
- Distress "MAYDAY" (grave and imminent danger) vs urgency "PAN-PAN"; 121.5 MHz is the emergency frequency.
- Read back runway, hold-short, altitude, heading and frequency instructions; "roger" is not a readback.
- ELT 406 MHz for satellite alerting; HF for long-range oceanic communication; CPDLC/ACARS for datalink.
Worked example
For 121.5 MHz, wavelength λ = 300/f(MHz) = 300/121.5 = 2.47 m. A quarter-wave antenna is λ/4 = 0.62 m. A shortened whip uses a loading coil to look electrically longer. This is why VHF antennas are short and why range is limited by line of sight, not power alone.
Traps
Using 121.5 for routine calls; reading back only part of a clearance; confusing MAYDAY with PAN-PAN; leaving the transponder in standby; and assuming 8.33 kHz channels are interchangeable with old 25 kHz frequencies.