Provoice question.

[AZScanner]

I keep reading how ProVoice uses a slightly different variation of the APCO25 IMBE vocoder. I'm curious as I don't think there's a provoice system near me to try this, but do the current crop of digital scanners try to decode it and it just comes out unintelligible, or do they stay in analog mode and all you hear is the digital noise? Enquiring minds and that sort of thing... :wink:

-AZ

 

[FPO703]

ProVoice is not APCO compliant.

 

[AZScanner]

ProVoice is not APCO compliant.

Right. I knew that.

Let me rephrase the question:

Lets say I had a frequency in my scanner that was a provoice frequency. Let's say my scanner is a Pro-96 or BC250D or similar digital model. If said scanner encountered a ProVoice encoded transmission on said frequency, would it:

A. Switch to digital mode and attempt (albeit unsuccessfully) to decode the signal?

or

B. Stay in analog mode and make an annoying noise like any other scanner would?

-AZ

 

[mikey60]

I tried it when I was in Florida last February. The Pro-96 seemed to stay in Analog mode. I was a ways from the tower though and it wasn't a clear signal to really be able to say for sure at the time.

Mike

 

[transam76]

I own a pro96, i live in an area where there is a provoice system, fire is anolog, but Pd are digital provoice on this system. Heres what happens, i have all the tags programed in. Fire comes in no problem, but police never come in, it just searches over the tag with no noise, don't even show that tag.

 

[AZScanner]

I own a pro96, i live in an area where there is a provoice system, fire is anolog, but Pd are digital provoice on this system. Heres what happens, i have all the tags programed in. Fire comes in no problem, but police never come in, it just searches over the tag with no noise, don't even show that tag.

Hmmm... OK.

Here's why I ask. I have a theory.

My admittedly crude uninformed theory is simply this: If you took the vocoder circuit from a MA/Com Provoice radio and fed it discriminator tapped audio from a scanner tuned to a provoice channel, it would decode the voice. :idea: Sure the current unit's won't trunk track it, but with some coaxing I bet etrunker could....

This would get around the legal ramifications because you are buying an already licensed piece of equipment and installing it in your scanner yourself. Everyone's already gotten their royalties from it long ago, so no one's gonna sue you. Hopefully.

I'm thinking MA/Com must sell replacement vocoders - why replace the whole radio if the vocoder goes on the fritz? One should be able to obtain a vocoder board by itself for this nefarious purpose.

What do you think? Workable idea or am I just dreaming here? In theory, it should work...

-AZ

 

[N_Jay]

If the vocoder is a separate circuit. which I doubt.
If the vocoder DSP does not need commands from the radio control processor.
If the vocoderinput is conpatable with the FM demod output.
If the Demod/descriminator can trace and demod the digital signal.
If you are realy good and realy lucky.

 

[SCPD]

Guys,

It's not just the vo-coder you have to worry about. The vo-coder "codes" the voice (samples and turns it into data - and vice-versa on the other end). Provoice does use the same IMBE vocoder as APCO 25. But this has nothing to do with the modulation method. There are many ways to modulate a carrier wave and Provoice uses a completely different method than APCO 25. And there can be additional "coding" done in the modulation method. In other words, they can mix up the bits how ever they want to before they put the signal on the RF carrier (even without encrypting).

 

[N_Jay]

Guys,

It's not just the vo-coder you have to worry about. The vo-coder "codes" the voice (samples and turns it into data - and vice-versa on the other end). Provoice does use the same IMBE vocoder as APCO 25. But this has nothing to do with the modulation method. There are many ways to modulate a carrier wave and Provoice uses a completely different method than APCO 25. And there can be additional "coding" done in the modulation method. In other words, they can mix up the bits how ever they want to before they put the signal on the RF carrier (even without encrypting).

I am not sure that the IMBE vocoder is the SAME between ProVoice and P25. It is the same family, but there are many subtelties to vocoding.
I do KNOW that the Channel coding is different. This how the bits are arainged and protected (error correction), and how extra features are carried.
I do KNOW that the modulation is different This is how the bits from the channel coding are put on the carrier.

 

[AZScanner]

I do KNOW that the modulation is different This is how the bits from the channel coding are put on the carrier.

Awww nuts, now he tells me... :roll: So it's mainly the air interface that's different more so than the voice coding. Thanks, thats all I needed to know.

-AZ

 

[N_Jay]

I do KNOW that the modulation is different This is how the bits from the channel coding are put on the carrier.

Awww nuts, now he tells me... :roll: So it's mainly the air interface that's different more so than the voice coding. Thanks, thats all I needed to know.

-AZ

The Air interface INCLUDES the voice coding.
It is all three pieces.
1 Voice Coding
2 Channel Coding
3 Modulation

I did not say the the voice coding is any less different that the others, just that I do not KNOW it is different.