Batboard

Hello to all:

I have been scratching my head on this. I have been working with a agency that came to me with problems when they are using certain Motorola OEM accessories (Transducers).

Apparently, they work great when using analog voice but the minute they switch over to Encryption the audio is not readable.

Any suggestions? There is a special interface between the headset and the radio (PTT Button Style) as well and I'm sure the hardware in the PTT that is probably the culprit. I'm sure it can be modified, just don't know where to start?

Might this transducer be the temple-mounted type I have used with the XTS line by chance?

This is the one that transfers via induced sound through the temple area.....

If this is the type, then I would probably surmise that the 'pickup' is not sensitive enough for the audio coming through the transducer, to be coded properly in an actual P25 setup.

Just my theory on the subject, nothing more.....

One other train of thought might be that the transmitted audio is muffled just enough to cause the vocoder to not be able to 'understand' or recognize spoken words, and instead of intelligible audio, you get scrambled eggs, which of course, is digital garbage the encryption can't deal with or correct, so neither can the vocoder.

Do you think adjusting the mic values on the radio may help or hinder?

I think you second theory is a good call.

I'm need to come up with a work around.

If the mic level was adjusted upward, you may find that distortion might come into play here, now that the TX level is increased, you maight stand the chance of increased noise pickup from nearby sources, like vehicles passing, sirens or some other form of loud audio getting into the microphone.

If you decide to increase the transmitted audio, it would probably be best if you did so, incrementally and make checks along the way as to the clarity and deviation of your audio.

Too much deviation, and you risk taking the audio well above the modulation acceptance bandwidth, and no longer fall within FCC guideines.

Change, test and retest, then make further adjustments as required, but never to the point of distortion or over deviating.