SDRTrunk -- first 1-2 secs of transmissions are constantly clipped

[rolypolyman]

I'm having constant trouble with SDRTrunk where the first 1 to 2 seconds of incoming radio traffic does not produce any audio. When I finally do hear audio it starts in mid-conversation, usually one PD unit in the middle of addressing another. Other times they are missed altogether. I thought it was lazy mike keying but it keeps happening and I can always see multiple seconds of audio on the waterfall with no sound before the sound channel opens up.

I found some references to a buffer problem that was fixed in an early 2018 version, but it doesn't seem to be working.

The system I'm monitored is a single frequency, a conventional (nontrunked) P25 Phase 1 system. I'm using an RTL 2832 SDR and the latest SDRTrunk, 0.4.0 alpha 9. I don't have any other channels loaded into the list. Even though there's no trunking I've been using this instead of SDR#/DSD+ because I couldn't get DSD+ to decode, while SDRTrunk simply works out of the box.

The first 2 seconds of some sample traffic (TDUs flooding the messages, normal):


Messages at the start of traffic, during the silence and when audio starts.


Any ideas on how to fix this?

 

[DRL-XM43]

2 things to check -

1. have you selected the right decoder (simulcast LSM - V - Normal C4FM) probably should be Normal for your case.
2. have you tried both tuner channelizers in view - preferences?

I have never seen it like in your screen shots? How many tuners are available for your traffic?

 

[rolypolyman]

Thanks, I went to Preferences and changed it from Polyphase to Heterodyne and restarted. Unfortunately the behavior is exactly the same, it's still cutting off traffic starts.

Trying LSM there's no audio at all when traffic appears in the waterfall, so it seems I need to be on C4FM. It's a small-town conventional system anyway. I also tried reducing Traffic Pool to 1 to see if it did anything, but the problem is still there.

When you mention you've "never seen it like in your screen shots", does it appear as if I'm using an old version? SDRTrunk is kind of weird in that there's no "About" page or any way to display the version number, so I don't really know how to confirm the build number, but all the files carry a file stamp of 2/17/2019.

I did manage to get SDR#/DSD+ to decode P25 by turning off the audio filter. Now that transmissions are coming in, I notice it isn't cutting off traffic starts like SDRTrunk is doing.

 

[dave3825]

SDRTrunk is kind of weird in that there's no "About" page or any way to display the version number, so I don't really know how to confirm the build number,

Sounds like you launch via the bat file. Jar files have build number in the name.

 

[rolypolyman]

Ah good point. I looked at the batch file and that pointed me to the /lib directory. So the jar I have is:

sdr-trunk-0.4.0-alpha.9.jar

 

[DRL-XM43]

Are you monitoring a bunch of single P25 phase 1 digital frequencies?

If so how many have you set up as channels?

How many dongles have you provided to SDRtrunk?

I don't know the system you are monitoring but I was confused when you said (TDUs flooding the messages ), is that what creates that long list of activity?

I use SDRtrunk to also monitor single P25 phase 1 channels, but each just activates on talk and dos not produce any flooding effects (that is the part I don't understand. )

The only time the list occurs is when trunking from a control channel.
























/

 

[rolypolyman]

I'm not sure whether the TDUs flooding the message status window are the problem. DSD+ shows the same flood of TDUs but doesn't suffer the clipped start audio. There are probably 20-30 TDUs per second when the repeater is keyed up but not passing voice traffic.

I'm monitoring a single P25 Phase 1 frequency (as shown on the first post). Nothing else is programmed in. There is only one dongle.

 

[DSheirer]

P25 traffic channels stream Terminator Data Unit (TDU) messages both before and after the voice starts. The Header Data Unit (HDU) indicates the start of audio and the LDU1 and LDU2 messages carry the actual voice data.

It looks like you're getting good decodes on the channel, but the 1-2 seconds of clipped audio at the start of the call is puzzling.

I'll open a bug report to look into the issue to see if there's anything I can fix for the next release.

An interesting side note ... in your screen shot #2, the LDU messages are also carrying Low Speed Data (LSD). Most of the systems that I've seen do not put any data in that field. I think that LSD was envisioned to carry low throughput data like talker alias labels or maybe even compressed GPS positions. It's a very small field with only 16 bits per LDU messages, so a complete piece of information will span multiple LDU messages.

Your screenshot is showing 0x8288F17DAAAAAA repeating. The repeating A value (1010) at the end is usually used to fill space at the end of a field. Those values don't look like ASCII text, so it may be an ESN or something that's setup unique in each radio.

Denny

I'm having constant trouble with SDRTrunk where the first 1 to 2 seconds of incoming radio traffic does not produce any audio. When I finally do hear audio it starts in mid-conversation, usually one PD unit in the middle of addressing another. Other times they are missed altogether. I thought it was lazy mike keying but it keeps happening and I can always see multiple seconds of audio on the waterfall with no sound before the sound channel opens up.

I found some references to a buffer problem that was fixed in an early 2018 version, but it doesn't seem to be working.

The system I'm monitored is a single frequency, a conventional (nontrunked) P25 Phase 1 system. I'm using an RTL 2832 SDR and the latest SDRTrunk, 0.4.0 alpha 9. I don't have any other channels loaded into the list. Even though there's no trunking I've been using this instead of SDR#/DSD+ because I couldn't get DSD+ to decode, while SDRTrunk simply works out of the box.

The first 2 seconds of some sample traffic (TDUs flooding the messages, normal):
View attachment 75375

Messages at the start of traffic, during the silence and when audio starts.
View attachment 75377

Any ideas on how to fix this?

 

[rolypolyman]

Thanks... I moved over for now to Unitrunker, which doesn't have the clipped start either, but SDRTrunk is pretty rock solid so I wouldn't mind coming back.

If you need a baseband sample, I can put that together in SDR# (don't see a place to do that in SDRTrunk). Not sure where to upload a 200-300 MB file though.

 

[dave3825]

Not sure where to upload a 200-300 MB file though.

Dropbox or Onedrive? In the past I have just googled "free file hosting" and usually something that worked..

 

[LD723]

Sorry to bump this thread if it's considered old but I have the same issue monitoring conventional P25 channels with the cut-outs

 

[DSheirer]

@LD723 I still have this on my TODO list to resolve this issue.

Denny