Radio theory and communication fundamentals
This section covers radio theory and communication fundamentals as tested in the NCAA PPL Communications exam: how VHF voice radio behaves, how to select and use a frequency, and how standard speech improves readability.
Core rules
- Civil VHF airband voice channels occupy 118.000–136.975 MHz and use amplitude modulation (AM). Transmission is normally simplex: one station transmits while others listen.
- VHF is essentially line-of-sight. A useful planning approximation for radio horizon in nautical miles is 1.23 × (√height in feet). Terrain and aircraft altitude strongly affect range.
- Channel spacing may be 25 kHz or 8.33 kHz; select the exact published frequency and confirm the active/standby display before transmitting.
- Use the ICAO phonetic alphabet and standard number pronunciation (tree, fife, niner; day-see-mal for the decimal). Speak at a normal rate, close to the microphone, and pause before releasing the push-to-talk switch.
- Readability is reported on a five-point scale; “readability five” means perfectly readable.
Worked example
An aircraft at 5,000 ft calls a station at 1,000 ft. Approximate radio horizon: 1.23 × (√5,000 + √1,000) = 1.23 × (70.7 + 31.6) ≈ 126 nm. The aircraft is 90 nm away, so direct VHF contact is likely, provided terrain and antenna siting are favourable. If contact fails, the pilot should try a higher altitude or a relay rather than assume the radio is unserviceable.
Traps
Confusing VHF with HF; assuming VHF is not line-of-sight; transmitting before the previous station finishes; using “three” instead of “tree” in noisy conditions; and failing to check volume, squelch or the selected frequency before blaming the equipment.