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P25 Smartzone Audio Delay

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acs680
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P25 Smartzone Audio Delay

Postby acs680 » Thu May 11, 2017 3:12 pm

I am trying to line up a conventional UHF system with a P25 Smartzone system so that when dispatchers are multicasting, it's not unintelligible in the cars due to the delay. I have experimented with a couple of delay boxes, and have gotten it fairly close, but am still having some issues. Will the latency on the P25 system vary or should it stay the same? I was told it should stay the same, but was also told the latency is "less than 200ms", which I've discovered to not be true. I would imagine since everything is all lined up when listening to multiple P25 radios, that there is some timecoding going on, but I just don't want to spend another week of trying to line them up only to have it shift.

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d119
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Re: P25 Smartzone Audio Delay

Postby d119 » Fri May 12, 2017 1:45 pm

acs680 wrote:I am trying to line up a conventional UHF system with a P25 Smartzone system so that when dispatchers are multicasting, it's not unintelligible in the cars due to the delay. I have experimented with a couple of delay boxes, and have gotten it fairly close, but am still having some issues. Will the latency on the P25 system vary or should it stay the same? I was told it should stay the same, but was also told the latency is "less than 200ms", which I've discovered to not be true. I would imagine since everything is all lined up when listening to multiple P25 radios, that there is some timecoding going on, but I just don't want to spend another week of trying to line them up only to have it shift.


It should not vary, especially if you are listening to a simulcast site. If it does, the variation would be minimal, and likely due to latency in the site transport.

I'm unsure why you would want to have such a configuration in the cars though, I'm curious what your application is.

You could use an Allen Avionics delay line on the UHF side of the house, that is what Motorola used to use to synchronize audio delays in the analog simulcast and paging systems of yore.

There is indeed time-coding going on in the P25 system. The comparator and channel banks (if this is actually a SmartZone system and not a true P25 trunked system) all time stamp the data going out to the sites, so that the audio all lines up at exactly the same time.

acs680
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Re: P25 Smartzone Audio Delay

Postby acs680 » Fri May 12, 2017 2:01 pm

Our primary radio system is UHF. The P25 statewide system is now our secondary and every car has both radios. Some of our specially teams do use our dispatch talkgroup on the statewide system full time however and that is why I want to multicast all calls for service. We are currently doing it on all hot calls, but this will take it a step further to all calls.

And, yes it is a trunked P25 Smartzone Omnilink system. I would imagine the same timecoding takes place to do the fact that radios on different towers hear audio in sync.

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Bill_G
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Re: P25 Smartzone Audio Delay

Postby Bill_G » Fri May 12, 2017 6:12 pm

I wouldn't even try. I'd tell people turn one or the other radio down. At some point everyone will be migrated over, and the need for multicast will be gone.

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d119
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Re: P25 Smartzone Audio Delay

Postby d119 » Sun May 14, 2017 10:17 am

Bill_G wrote:I wouldn't even try. I'd tell people turn one or the other radio down. At some point everyone will be migrated over, and the need for multicast will be gone.


I'm with William (as always) on this one. This is just a disaster trying to do what you want to do. Your users need to be educated on proper radio use to avoid the problem you are having.

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Bill_G
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Re: P25 Smartzone Audio Delay

Postby Bill_G » Sun May 14, 2017 6:47 pm

d119 wrote:
Bill_G wrote:I wouldn't even try. I'd tell people turn one or the other radio down. At some point everyone will be migrated over, and the need for multicast will be gone.


I'm with William (as always) on this one. This is just a disaster trying to do what you want to do. Your users need to be educated on proper radio use to avoid the problem you are having.


The piece he is not going to be able to time compensate for is the subscriber decoder time. That will vary with the BER adding tens of mS if the radio is having to apply FEC to a lot of packets. I've heard portables get out of sync with each other across the room listening to the same site.


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