Any way to quiet the Metro Fire dispatch tones?

gmclam

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Sep 15, 2006
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Fair Oaks, CA
The real problem is that the speech is undermodulated on the VHF channels. For me the solution is to monitor dispatch from A1 & B1 on the trunked system and mostly ignore the VHF channels.
 

johntodd

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Jul 22, 2006
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Rio Linda, California
That's what I'm doing, on the P25 system. Seems like dispatch, especially the three attention/alert tones are SO much louder than everything else on the system. One important point; This is only on the automated dispatch system. They are doing live dispatch this morning, and it's much lower in volume.
 

WB9YBM

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May 6, 2019
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Niles, IL
I listen on a BCD536HP, and the Metro Fire dispatch tones are piercing! Any way to quiet them?
The only way I can think of is the DIY approach: find out their frequency (some frequency counters go down into the audio range), then use a 567 I.C. wired to that frequency. Long story short: when the 567 detects the right frequency, it can be used to mute the speaker. It's been around for several decades so it's a time-proven device, is multi-sourceable (so it's pretty much always available and costs only pennies). It's used often in DTMF tone detection/decoding.
 

ko6jw_2

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Santa Ynez, CA
I found many years ago that a DSP speaker treated tone outs as noise because they are continuous whereas speech was variable and was not affected. It should not matter whether the system is digital or analog because you will be processing the decoded audio. This won't eliminate the tones altogether, but it may make them less piercing. You also don't need to determine the exact tones.
 
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