P25 vs Analog - Squelch and Coverage question?

[g8tzl2004]

I'm just researching and getting up to speed with P25.

I have a couple of really basic questions:

- Is there a "squelch adjust" softpot when using P25. One of the 1st things I do with my Moto analog stuff is to use CPS to lower the SQ level for weak signal working. Most analog radios are set with the SQ level relatively high so you might miss really weak but copyable signals. Is there such a thing as squelch level or "equivalent" when using P25. I guess I want to hear really weak "robotic" P25 signals rather than just 100% "clean" P25 signals.

- Using analog, I like to hear the squelch tail "chuff" in a noisey environment so I know when the peson I am working has finished talking. Using P25 its difficult to tell when the other person has finished talking as there is no "chuff"!!! I presume you can program an "end of over" bleep or something?

- If I was receiving a very weak noisy analog signal which was just copyable. Under the same conditions, would a P25 signal still be copyable or do you need stronger signals at the margin for P25?

Thanks

[judoka]

There isn't normally a squelch adjust for P25, the detector works down into the noise floor. The reason that you need one for analog is because strength of signal is the only distinguishing feature between "noise" and "signal" (unless you use PL/DPL). The P25 signal has a synchronization burst at the start of each frame so if you detect that, you have a valid signal.

Not sure if any vendor has an end of over bleep

Your final question is a tricky one - Under some conditions of weak noisy signal, the P25 signal would be pretty good with some odd noises (bad audio is different for digital and analog). Under some other conditions, there would be nothing at all or short bursts of good audio while the receiver hunted for frames. From experience, the coverage of P25 is as good as analog in noise limited environments (no interference) but there isn't much warning of cut-out.

[g8tzl2004]

Thanks for the useful feedback

[N4KVE]

Not sure if any vendor has an end of over bleep

I know this is a P25 thread, but the Moto TRBO radios can be programmed to do this. GARY N4KVE

[N4DES]

From experience, the coverage of P25 is as good as analog in noise limited environments (no interference) but there isn't much warning of cut-out.

I do agree with this. When we were dealing with the pre-rebandingsite noise issues I did some tinkering and even under the most extreme circumstances the digital outperformed the analog with everything else being the same. That being conventional mixed mode station, identical radios with the receiving one programmed for mixed-mode RX and just took the TX radio and went back and forth between 2 modes at the same location, etc. When the analog mode was noisy the digital was 100%. I didn't go as far to figure out the noise figure, but it was bad enough that it would even affect the CTCSS decoding but the NAC was 100% decoding and no lost bits.

Of course it was not a lab environment and the site density could have changed during the course of the test, but it made a believer out of me as how well the APCO25 works and now with improved firmware versions in the radios I wouldn't doubt that it would even be better now.