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What is the technical term for these tones (often multi-frequency) which I uploaded here that radio devices used by Police, EMT, etc produce before or/and after a voice message and why they differ in pitch, frequency and other sound characteristics? Who did first developed the idea of them? Are these sounds registered for each manufacturer?

Someone referred to them as Squelch, which I'm not sure, because I couldn't find any sound sample for them online.

Also note that I'm not referring to any noise here. I'm looking for a term to address those certain tones that radio devices make on their own, like a musical instrument!

Please note that the sound file I posted is a mix of 2 different sound files from different sources.

I noticed that vintage Eurosignal system was used to produce sounds/tones similar to those that two-way radios make, a series of tones which vary in frequencies.

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The most probable signal to be sent out at the start of a Police/EMT transmission is a Digital Selective Calling identifier and/or selector. This is a series of audio tones which digitally identify the transmitter and select the receiver or group of receivers which are to receive the call.

Your best bet for finding information on this is to look for Digital Selective calling or DSC in the owners manual. Also this http://www.w2sjw.com/radio_sounds.html has a collection of examples.

On less sophisticated equipment a beep is sometimes added when the unit stops transmission. This is referred to as a roger beep or jokingly as an idiot beep and is used to indicate end of transmission without using good procedure.

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  • \$\begingroup\$ Thanks a lot. "Roger Beep" that you mentioned earlier seems to be correct, but I don't know if "Idiot Beep" is correct or not. \$\endgroup\$ Jan 25 '17 at 10:04

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