Radio waves and your VHF radio — transcript

00:00:00.400 --> 00:00:04.815 Your VHF radio: how its signal travels, and how to keep it working.

00:00:06.400 --> 00:00:09.759 A radio transmitter sends out electromagnetic energy.

00:00:09.759 --> 00:00:14.052 It travels at the speed of light, about 300,000 kilometres a second,

00:00:14.052 --> 00:00:17.162 as regular waves in electric and magnetic fields.

00:00:18.900 --> 00:00:25.275 Four properties. Amplitude: the height of the wave, its strength. Wavelength:

00:00:25.275 --> 00:00:31.650 the length of one cycle. Frequency: cycles per second, in hertz. Attenuation:

00:00:31.650 --> 00:00:37.943 the signal weakens with distance. Higher frequency means shorter wavelength.

00:00:38.293 --> 00:00:43.273 Sound needs air or water, and moves at about 340 metres a second.

00:00:43.273 --> 00:00:47.950 Radio needs no medium. And a receiver tunes to one frequency,

00:00:47.950 --> 00:00:50.440 while your ears hear everything.

00:00:50.790 --> 00:00:54.371 Storm on the horizon: you see the lightning first, then hear the thunder.

00:00:54.371 --> 00:00:55.388 Light outruns sound.

00:00:57.790 --> 00:01:03.399 Aviation uses HF and VHF. HF reaches further, but sounds poorer.

00:01:03.399 --> 00:01:09.784 VHF is short range and clear. Its airband runs from 108 to 137 megahertz:

00:01:09.784 --> 00:01:14.874 navigation aids below 118, voice from 118 to 135 point 95.

00:01:15.224 --> 00:01:19.299 Quick check. 124 point 7 megahertz. Which part of the airband is that?

00:01:21.224 --> 00:01:25.221 Voice. 118 to 135 point 95.

00:01:25.571 --> 00:01:30.099 VHF travels in straight lines. Cloud and darkness don't block it, but hills,

00:01:30.099 --> 00:01:33.863 terrain and buildings do. The Earth's curve hides low stations,

00:01:33.863 --> 00:01:36.569 so the higher you are, the further you reach.

00:01:39.071 --> 00:01:44.092 Rated coverage is where reception is guaranteed. ERSA publishes it. Beyond it,

00:01:44.092 --> 00:01:47.461 you may still hear, but don't count on it. Low down,

00:01:47.461 --> 00:01:50.957 a drone crew has less range than an aircraft overhead.

00:01:53.071 --> 00:01:55.816 Down in a valley, the ridge blocks calls you need.

00:01:55.816 --> 00:01:58.400 Know your radio's limits before you rely on it.

00:02:01.071 --> 00:02:03.246 Press to talk, release to listen.

00:02:03.246 --> 00:02:07.404 A stuck mic keeps transmitting and blocks everyone on frequency.

00:02:07.404 --> 00:02:12.266 Squelch sets how sensitive the speaker is when nothing's received. Hissing?

00:02:12.266 --> 00:02:13.610 Turn the squelch up.

00:02:14.071 --> 00:02:19.114 Not working? Check in order: battery charged, antenna fitted, volume up,

00:02:19.114 --> 00:02:23.397 squelch set, the right frequency, and push-to-talk not stuck.

00:02:25.071 --> 00:02:29.646 Everything on the airband stays confidential unless you're authorised.

00:02:29.646 --> 00:02:33.963 Operational calls only: no private chat, nothing false or obscene,

00:02:33.963 --> 00:02:35.703 and no improper callsigns.

00:02:36.071 --> 00:02:43.072 Recap: straight lines, rated coverage, squelch for hiss, and operational calls only.

00:02:43.422 --> 00:02:48.281 Final check. You switch on and hear a loud hiss. Which control do you adjust?

00:02:49.922 --> 00:02:52.430 Squelch. Turn it up until the hiss stops.