APX6500 DTMF problems

[jacklacher]

Has anyone else had any problems with DTMF dialing on APX mobiles?
I have a customer who is using pre-programmed DTMF codes to set off weather warning sirens in their county. They have 4 APX 6500s and none of them work well. The Federal Signal siren controllers are having trouble decoding the DTMF characters from the APX radios, but it works fine when using Harris or Vertex radios. I tried to slow down the timing but that didn't help either. Any ideas?

[Jim202]

You haven't mentioned if these radios are using a repeater or not.

I ask because DTMF decoding is not very tolerant of distortion. Most repeaters are not very well adjusted for tone throughput. Generally the radio techs tend to put the audio into compression. This will kill the ability to pass DTMF tones through a repeater.

You really need to put the user radios on a service monitor and see what the voice deviation and the DTMF deviation actually is. The DTMF tone level will not work if it is any where near the voice level. It will work much better if it is more like 50 to 60 percent of the voice level.

Another issue is DTMF tone twist. I will not go into it here, but it wouldn't hurt to do some research on the subject.

Jim

[jacklacher]

The DTMF codes from the APX won't work at all through the repeater, and they have about a 50% success rate when bypassing the repeater. I can't blame the repeater though because all the other radio models worked through the repeater.

These are brand new siren controllers we were working with, and the technician from Federal Signal told me their decoders would work even with the most severe tone twist errors.

I think you are probably right about the deviation being a problem, but can I adjust the DTMF deviation without affecting the voice deviation?

[techtonics]

IIR dont the APX radios digitally reproduce analogue audio?

I was in a class recently and they said that the APX series digitizes everything and reproduces analog