What does "pilot" do on wireless mic systems?

[peza2010]

What does the pilot option (that can be turned on or off) do on wireless mic systems? A quick google search brought up things like "pilot tone" and "squelch" so what are these two options and what do they do ?

[Bobbsy]

An FM receiver generates a high level of broadband noise when it's not receiving a signal...enough noise to be unpleasant to listen to and possibly damage speakers. To circumvent this, a squelch circuit is generally incorporated. At the simplest, this turns off the receiver output when a certainly level of signal is not being picked up. However, this form of squelch can be fooled into unmuting when an interfering signal is picked up.

 

A better system to handle the squelch is a high-frequency pilot tone to the transmitter signal. The receiver checks incoming signals to see if the pilot tone is present. If not, the receiver assumes that the signal is not from its own transmitter and keeps the receiver muted even if the interfering signal is very strong. This form of squelch is generally referred to as "pilot tone" or "tone coded" squelch.

 

Bob

[paulears]

Pilot tone in radio systems is a super (or sub) sonic tone superimposed on the transmitted audio that can be detected at the receiver. It gets filtered out so isn't audible, and is quite low level anyway, but means that the receiver will not (if pilot tone is on) open the squelch and let you hear the audio it is receiving. So a Sennheiser receiver, even on the same channel, will not respond to a transmitter made by somebody else (or of course, even from another Sennheiser, if the pilot tone is off).

 

Squelch is a signal level based mute. If the signal level drops below a certain point, the squelch closes and you don't hear it. The danger is setting squelch too fine, so that it chops in and out. Usually, because we only want decent quality audio, there's not really much point setting it right on the edge, because the unpleasantness of the sound with the wooshes and crackles is often worse than no audio at all.

 

EDIT

Don't you just hate it when that happens!

[Rob_Beech]

To add, You really do need to set the squelch correctly. Too low and you may get unwanted noise when the mic goes out of range, too high and you may cut the mic of when you're working to it's RF limits. On a decent piece of equipment, the highest squelch level is quite strict, you'll find that you are not getting any audible RF interference when the mute kicks in, so if you're working in less than ideal environments its usually safe to turn the squelch down a bit. When push comes to shove, it's often better to have a little RF noise than the mic muting as they take a couple of seconds (which feels like the best part of a calendar month) to unmute again afterwards.

 

In some pro settings directional antenna setup in the correct way with a high squelch setting ensures that the mic is muted whenever a person is not in the correct place, in theory this should stop you needing to mute a mic when they walk off stage as it would do it automatically, but then again, in that same professional setting, I don't know anyone prepared to take that risk.

 

Rob