[op25-dev] Why can't I hear fire tones?

'William Becks' wllmbecks@gmail.com [op25-dev] op25-dev at yahoogroups.com
Sat Jun 16 20:52:58 UTC 2018

I don’t think there is an easy answer because op25 uses a software vocoder written to decode speech as opposed to commercial P25 radios that employ the DVSI chips that were revised and redesigned to pass tone signaling, DTMF, Knox and single tone.   If it’s important to your application to pass the tones to the listener then you should consider using a commercial radio or scanner that doesn’t affiliate or cause unwanted transmission on the public safety communications system of interest.


There are a number of surplus p25 radios that could be used to accomplish this task.  The major fly in the ointment would be if your system is a Phase-II system that would require a must more costly alternative.   Perhaps one of the active programmers that regularly contribute to op25 will jump in here to do a better job of explaining the software vocoder in P25 that I am capable of doing.


Lastly, I gather that your Uniden scanner passes the alert tones, so is there a reason that you can’t use it or a similar receiver for your application?


Good luck,





From: op25-dev at yahoogroups.com [mailto:op25-dev at yahoogroups.com] 
Sent: Saturday, June 16, 2018 3:31 PM
To: op25-dev at yahoogroups.com
Subject: [op25-dev] Re: Why can't I hear fire tones?



I figured they may not have been used for paging, I didn't know what to call them. The problem is I cannot hear those alert tones on OP25 and can't understand how I may fix it on OP25. They are quite important for listeners, as they get the listener's attention when a new fire call comes in.

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