SDRTrunk Site Preference List

[Twister_2]

Is there a way to create a preference order for P25 sites? My area has a huge simulcast cell surrounded by individual sites. Since the simulcast cell is so large, almost every active talkgroup is affiliated on it where as the surrounding sites are more hit or miss once you get off the main dispatch talkgroups.

I try to provide the highest quality audio for my calls node and audio feed but that's impossible on the simulcast site due to intermittent multipath distortion. I'm able to use surrounding sites for the main talkgroups that I'm confident are almost always lit up on those sites, but it would be nice to just make those surrounding C4FM sites preferred unless the talkgroup is only coming up on the CQPSK site.

 

[jtwalker]

Not in SDR-trunk (to my knowledge) but you could send all the sites to Broadcastify and let it pick and choose which to use to make available on the calls node(s).

 

[Twister_2]

Not in SDR-trunk (to my knowledge) but you could send all the sites to Broadcastify and let it pick and choose which to use to make available on the calls node(s).

Correct me if I'm misunderstanding but I don't think that will work because any talkgroup could be on or off at either site at any time. You almost need a prioritized list of which sites to use first. If I just tell it to ignore simulcast for certain talkgroups, I'll be SOL when those talkgroups are not affiliated on the other site.

 

[jtwalker]

My suggestion would be to send all TGs for all sites.

 

[Twister_2]

I'm not sure how the second part of your suggestion "let it pick and choose which to use to make available on the calls node(s)" is accomplished.

 

[jtwalker]

There is duplicate call rejection built into Broadcastify so if you send same call from multiple sites it should detect it and only pick one to put into calls node. I can’t spout exact details of how this algorithm works but maybe someone else can.

 

[Twister_2]

There is duplicate call rejection built into Broadcastify so if you send same call from multiple sites it should detect it and only pick one to put into calls node. I can’t spout exact details of how this algorithm works but maybe someone else can.

It selects the node provider based on latency and other related factors. It won't know one sounds slightly worse because it's simulcast vs the other.

 

[Enforcer52]

You either turn a tower on or you turn it off, you either turn a channel on or you turn it off, you either turn Duplicate Detection on (SDRT chooses which to use, no way to tell it) or you turn it off.

NO way for SDRT to tell which one sounds the best, or choose a certain tower only when the transmission is on both simulcast tower and other tower.

 

[Twister_2]

NO way for SDRT to tell which one sounds the best, or choose a certain tower only when the transmission is on both simulcast tower and other tower.

I have no interest in the former but the latter would be a straight forward solution to the issue brought forth in the original post.

 

[Enforcer52]

There is no way for SDRT or the computer to determine which sounds better the simulcast tower or the other tower. And I doubt the author is going to try and wright an algorithm to use the other tower, when both towers receive a tgid.

But good luck asking him.

 

[Twister_2]

Not sure why you keep bringing up how the program cannot determine which site sounds better. That is not my goal. You’ve made your point clear a few posts ago. Putting site preferences into the duplicate call algorithm would be helpful. Have a wonderful day.

 

[GTR8000]

I've got a number of computers in various locations monitoring multiple P25 simulcast cells with varying hardware (RTL-SDR.com, NooElec, FlightAware, Airspy, SDRPlay) including locations where the receivers are getting hit with signal from 3-4 subsites of varying signal strength + reflected signals...and SDRTrunk handles it all well. I'm surprised that you're having trouble with decoding simulcast using the software.

Assuming you have that site's control channel setup for LSM, and you're likely already using polyphase decoding, have you dialed everything else in? PPM correction? Is auto-PPM correction enabled? Is your gain optimized so that it's not too high (and of course not too low)? What hardware are you running and at what bandwidth is the tuner set to? Are some of the cell's traffic channels at either end of the spectrum being covered? If so, those channels can tend to fade, as you're never going to get the full bandwidth for the hardware. A standard dongle specs call for 2.4 MHz of bandwidth, but the other .2 MHz on either edge is going to be weak and will fade out, so 2 MHz is more realistic unless the signal is quite strong to overcome that fading. Likewise you're not going to get the full 10 MHz from an Airspy unless you've got a very robust signal.

And of course you might consider attenuating your signal if you're getting hit too hard from adjacent subsites if you have a nearby strong subsite. That should reduce some of the competing signals hitting your receiver.

 

[Enjoi19]

I'd be curious to see your event log too - are you encountering many sync loss messages in there? I often have used that to help really narrow down signal settings on SDR Trunk.

Trunk-Recorder has an option to prioritize recording talkgroups off specific sites - perhaps worth putting in a feature request with SDR Trunk to see if it's an option to add at some point.

 

[Twister_2]

I've got a number of computers in various locations monitoring multiple P25 simulcast cells with varying hardware (RTL-SDR.com, NooElec, FlightAware, Airspy, SDRPlay) including locations where the receivers are getting hit with signal from 3-4 subsites of varying signal strength + reflected signals...and SDRTrunk handles it all well. I'm surprised that you're having trouble with decoding simulcast using the software.

My setup handles it "well" to most people but as you'll see below, there are a few instances of distortion. I'm not sure if you've ever used early Radioshack scanners but I get random noises reminiscent of those scanners on my decode. The only radios that work 100% of the time on this system are subscriber units. Over the years I’ve tried everything up to the SDS200. That is pretty good but not great when compared to an APX or older XTS/XTL. The Airspy/SDRTrunk is actually a little better than the SDS with decode but the audio still sounds like an early 2000s Radioshack P25 scanner with how it processes the audio. Now onto your questions.

have you dialed everything else in?

Yes

PPM correction?

0.1ppm corrected with max error of 0.1ppm but it usually stays at 0ppm error.

Is auto-PPM correction enabled?

Yes

Is your gain optimized so that it's not too high (and of course not too low)?

Yes

What hardware are you running and at what bandwidth is the tuner set to?

I've tried multiple RTL-SDRs (ranging from cheap blue plastic to the better aluminum case) but right now I'm running an Airspy and it works WAY better than anything else I've tried. It's at 10 MHz but my furthest VC is approximately 2 MHz away from my CC (500 to 502 MHz).

Are some of the cell's traffic channels at either end of the spectrum being covered? If so, those channels can tend to fade, as you're never going to get the full bandwidth for the hardware. A standard dongle specs call for 2.4 MHz of bandwidth, but the other .2 MHz on either edge is going to be weak and will fade out, so 2 MHz is more realistic unless the signal is quite strong to overcome that fading.

They aren't that far away, at least that's how I feel. I've watched it over the years and I can't find a correlation between VC frequency and poor decode. Poor decode really just means missing syllables in a small fraction of transmissions and random noises, especially at the end of transmissions that aren't there when listening on a APX or simply on the other site with the same tuner.

For a time I ran two channels on SDRTrunk, one for simulcast and another for a standalone site. The transmissions would play back to back and it was very easy to tell which ones came from which site(s).

 

[dave3825]

I'm running an Airspy and it works WAY better than anything else I've tried. It's at 10 MHz but my furthest VC is approximately 2 MHz away from my CC (500 to 502 MHz).

Just curious, What site(s) are you monitoring?

 

[Twister_2]

Just curious, What site(s) are you monitoring?

Simulcast and Derry and/or Ellendale.

 

[dave3825]

Simulcast and Derry and/or Ellendale.

Those 3 sites span 2.525. Which Airspy do you have and what are the sample rate choices in SDRT?

 

[Twister_2]

Those 3 sites span 2.525. Which Airspy do you have and what are the sample rate choices in SDRT?

I have the 10 MHz Airpsy. For the longest time I monitored simulcast only. All VCs give me the audio issues. It’s multipath. I’ve been around long enough to know what it sounds like. The standalone sites sound perfect, even sites with weaker signals.

 

[dave3825]

What are all the sample rate chooses listed in SDRT with your Airspy?

 

[Twister_2]

What are all the sample rate chooses listed in SDRT with your Airspy?

2.5 and 10