That is with a heavy simulcast P1 system and no problems. Maybe phase II is more taxing?
MicroP25RX
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This is a mix of P1 and P2 on an extremely busy simulcast system.
The system I'm monitoring is strictly P2 and I have no issues to report other than a slight garble in audio which I suspect is due to the transmitting tower being just over a mile away.
P2 audio doesn't sound as good as P1. It is a "half rate encoder", so it is pretty amazing it sounds as good as it does. You should be able to park under a tower no issues.
The amazing thing about P2 is the ability to fit two voice conversations into a single 12.5 kHz RF channel. Obviously, there has to be some trade-off. It can sound pretty good. Obvioulsy, the radios, mics, speakers all play a part in the sound quality. If you are actually having some issues with demod/decode, then it could cause degraded sound as well. You would see a high error rate during voice in this case. For those cases where intermod is an issue, I will be announcing a new product soon.
They are not squeezed in side by side as two 6.25 kHz channels, if that's what you're suggesting. They are alternated by time slot, hence the T in TDMA. Each voice slot uses the full 12.5 kHz bandwidth, minus some overhead for signaling. Oh and the AMBE+2 vocoder may be "half rate" compared with IMBE, but that doesn't mean it's worse. In fact, it's better by a number of measures. Just look at the improvements in regeneration of tones. IMBE is much less efficient than AMBE+2, offering less groups for range of tones. AMBE+2 also does better with background noise suppression. But anyway, this really isn't the place to be discussing vocoders I suppose.
Is it always garbling? If not, it could be the SU's location, uplink issue, or a different transmitter or antenna on the same tower that is dominant for your location. It should not be garbling full time.
I only notice it on one talkgroup and only from dispatch. The responding units are clear.
I specifically said "single 12.5 KHz RF channel". lol. How did I suggest otherwise? There are actually 2 slots per channel, so you can fit two voices/slots in a single 12.5 kHz channel (plus some control information). That is the whole point of TDMA. As I said, it is amazing it sounds as good as it does, but P1 does sound better to me.
That sounds like it could be a system issue.
dustinsterk
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I noticed another lockup today with the latest FW. I was messing with the speaker when it happened....probably just a coincidence but I will continue to keep an eye on any pattern.
Do you mean you were messing with a connection on the 3.5mm jack? Or messing with audio/speaker settings in the configuration menu?
Yes, what maus92 said... I have this same issue with our dispatch center. The tone-out and Locution dispatch voice are crystal clear, as are the responding apparatus. The human at the console, however, is mostly always garbled, and I noted this since before I even got a P25RX-II, even on the patch to their analog VHF FM frequency.
Sometimes there are problems with the uplink. I have one talk group here for an analog patched system that sounds horrible all the time. It isn't just because it's analog. They are obviously missing lots of frames on the uplink.
I finally realized what you are thinking. It is true that if only one of the voice slots is active, it will not result in a change to the occupied channel bandwidth. That is because the symbol rate is a constant 6000 symbols/sec regardless whether there are 1 or 2 slots active. Ultimately, it is this rate combined with the deviation and pulse shaping that determines the occupied bandwidth. It is incorrect however to say that each slot uses the full 12.5 kHz bandwidth, otherwise there would be no room for the other slot and control information. The reason that the vocoder is half rate, is to reduce the required bandwidth by one half. This is what allows two active voice channels into a single 12.5 kHz channel (utilizing TDMA to interleave). I agree that it does sound good despite the bit rate being cut in half!
Received the Slinkdsco antenna today. It is a good antenna. Thanks!
dustinsterk
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There is a new version available. Multiple tone pairs are decoded and displayed per call. The display format is now the index values (1-72) from Figure 2 in the document you referenced earlier for two-tone decoding. The next release will support configuration of up to 16 tone pairs, a tone-match TG timeout, GPIO options, and an alias for tone pairs.
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