What causes the ‘static’ sound on my two-way radio?


(Asked by Preeta from Newcastle)

This is actually a pretty common question. However, just because it is a common query does not mean that it isn’t a valid one. Radio static is something that most people simply take for granted and never question (which is actually quite silly of them, really). Anyway, the point is that I’m glad you asked.

Essentially, radio static is the sound you get when there is no broadcast on a specific frequency. This can mean anything from, ‘my friend/colleague doesn’t know how to use the radio’ to ‘the zombies have taken over and we’re all going to die!’ (As well as any number of options in between).

Pretty much every signal receiver (from your two-way radio to your TV) has what’s called a ‘squelch’ circuit built in to it. The ‘squelch’ function simply monitors signal strength and, where necessary, cuts it off. Therefore, if a signal drops below a certain, pre-determined level, the circuit simply mutes (or ‘squelches’, if you prefer) that signal.

The audible ‘static’ sound you refer to is the delay between the end of the broadcast and the squelch circuit realizing that there is no broadcast coming through to the receiver and therefore muting the sound.

Conversely, if all you can hear is static, then it is simply caused by the absence of anything being broadcast. In either instance, the squelch circuit will step in and mute the sound, effectively cutting the noise. 

If you are only getting static and you are unable to hear anything at all on your two-way, then it seems likely that you are set it to the wrong frequency, or else you are using an incompatible type of radio to the person with whom you are attempting to communicate, either that or your radio is buggered.

Of course, the zombie apocalypse is an unlikely cause for radio static; however, I don’t think I’ve ever seen a zombie movie that didn’t feature it in some capacity, so I thought it was worth a mention.

I hope that answers your question, Preeta.