DSDPlus Fast Lane Missing Voice Channels

Clear4Code7

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I'm using DSDPlus Fast Lane in a dual SDR configuration to monitor an NXDN 4800 system in SoCal and am having intermittent problems with it following talk groups. For the most part, everything is awesome. But frequently it misses part of the convo or the entire thing. I'm currently holding to a specific talk group, but that doesn't seem to help too much.

I've tried the following and was curious if there's anything more I could do?
  • Disabled all other protocol decoding aside from NXDN-4800 (-fn)
  • Disabled wav/mp3 output (-O NUL)
  • Optimized each SDR using ds, dd, and dv parameters
The control channel indicates hardly any error in the output/log, if it helps.
 

cg

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Did you populate the DSDPlus.FREQUENCIES file for that system?

chris
 

Reconrider

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If you're missing conversations, it's your antenna signal to the system itself. Buy a better antenna and you should have less issues
 

slicerwizard

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Obviously a DFA system. You need to pay attention to the specifics of the problem you're having (and perhaps communicate them to us) - are only certain voice channels having a problem or is it random? What exactly happens? Does the VC side fail to tune to voice traffic? Is the tuning on frequency? Does VC DSD+ decode anything?

A video illustrating the problem would likely result in better help.
 

Clear4Code7

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What’s a DFA system?

I’ll grab some screenshots, but the problem seems to be parts of the conversation are being missed. Usually most of the voice traffic is being received, but several times I’ll either miss the initial call from the vehicle to dispatch or I’ll miss the first part of what they’re saying.

One thing I did notice is the counter on the control channel seems to always indicate a higher value than the voice channel.

For example, the control channel may indicate 3 seconds of traffic on the voice channel, but the voice channel itself indicates 2 seconds.
 

Clear4Code7

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Here's an example of some missed voice traffic:
  • 17:52:02 - CC indicates channel 17425 with 2 seconds voice. Corresponding voice channel shows only 1 second of voice (cuts off first part of traffic)
  • 17:52:12 - CC indicates channel 34432 with 3 seconds voice. Voice channel doesn't indicate any traffic.
  • 17:52:16 - CC indicates channel 34776 with 1 second voice. Voice channel doesn't indicate any traffic.
In the second screenshot, for the control channel at 17:36:47 where 3 seconds of voice traffic was occurring on channel 34104, the spectrum display for the VC never indicated it tuned to 34104.

1623805378176.png
1623807805717.png
 
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cg

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Perhaps the signal is so narrow with the 3.25KHz channels that it needs more exact tuning. Without seeing the FMPx window, I don't know what SDR you are using but I would try to get the PPM adjustment as good as I could and if using FMP24 then try turning off the auto tune (a)

chris
 

cg

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DFA is direct frequency assignment. It simply means that there is frequency information sent in the data stream rather than channel information that references a preprogrammed list. Makes adding new channels easier by not requiring every radio be touched.

chris
 

Clear4Code7

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For the SDR, I'm using this: https://www.nooelec.com/store/sdr/sdr-receivers/nesdr-nano-three.html

I'm using the default settings for FMP24 (FMR24 -rv -i2 -o20002 -P0.0). I'll have to work on getting video. For now, here's a screenshot of a missed transmission (I enabled the extra CPU loading about 30 seconds prior to the missed transmission).

The control channel at 18:55:48 shows a 4 second transmission, but there's no corresponding traffic file or tuning in FMP24.

1623895069637.png

More screenshots of missed traffic where the voice channel is never even tuned.

How does DSDPlus interact with the FMP24 process for receiving the frequency guidance? Is it only via the .traffic files? TCP?
 

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Clear4Code7

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Anyone know how DSDPlus Fastlane directs the FMP24 process to tune to a frequency? I'm still missing quite a bit of conversations that are picked up by the control channel, but never even attempted to tune by FMP24 (no tuning attempt ever indicated in console output for the missed conversations).

I've tried the following, without success:
  • Exempted folder from Windows Defender
  • Holding on single talkgroup
  • Not holding on single talkgroup
  • Decoding only NXDN-4800 (other protocols deselected)
  • Swapped SDR dongles between voice and data channels
  • Verified CPU utilization is low
 

AM909

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@AtlasLabs: The first image is pretty tough to read, and the attachment image is not readable, due to low resolution. Not sure where the problem is there.

What I can see in the first image is that you are using port 20002 on at least one of the instances, so I'm going to guess that you are using 20001 on the other. I remember someone mentioning that the ports should be separated by 10 because of a potential bug in the way additional port numbers that are required are managed.

BTW, you can turn off the "records loaded" noise in the DSD+ windows by pressing B when one of its windows has focus to cycle through the options. (Anyone know if there's an (undocumented) command-line option for this?)

Try not using the -d[dsv] options, which may not be necessary.

Are the problems isolated to the 45x channels? If so, it could be that, if your signal is just marginal at the 50x CC and voice channels, you could fall out on the 45x channels (at least 10% bandwidth is a lot to ask from most antennas).

Is the FMP window showing BW:4k in the title bar (set with -b-4 option to FMP24)?

Also try pressing T when the FMP window has focus to switch between "tight" and "standard" filters (set with -t0 or -t1 option to FMP24).

Not that I think it's related, but just for good measure, as someone else mentioned, make sure your FMP24 command line -P values are correct because of the narrow (usually 6.25 kHz) channel spacing, and that auto-tune is disabled (-a0 on the command-line) – sometimes auto-tune can cause it to try to lock an adjacent channel. With auto-tune enabled it tells you in the title bar what the offset it's using is. E.g. "corr=0.0 ... f:507.850000+710" means you specified -P0.0 and it needs -710 Hz, which is -1.4ppm, so you should specify -P-1.4. [Edit: I reversed the polarity of this after playing with it. You can move the correction in 0.1 ppm increments with the p and P keys to watch the changes live. Note that there are some inconsistent results in the few 0.1 increments around the right one.] If it then shows an offset close to zero after the frequency (e.g. f:507.850000-23), you can add -a0 to the command line to turn off the auto-correct. This is assuming reasonably stable SDRs, hopefully TCXO, though I have an RTL-SDR.com v2 that only moves between -1.625 ppm cold and about -1.250 ppm warm, and stays pretty close to that afterwards. YMMV.
 
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AM909

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...Verified CPU utilization is low...
BTW, if I understand it correctly, low CPU utilization can actually be bad? You may want to use -e1 to cause "Extra CPU loading enabled" on one of the dongles only. I forget where the details of the issue are described, but I confirmed it was necessary for me, going from dropping a buffer every 5-10 seconds to no drops at all. [Edit: Any suggestions on how to solve this problem when running SDR#? Sometimes, I get no drops, while other times, I get a drop every few seconds. I haven't been able to correlate it with CPU usage yet.]
 
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Clear4Code7

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Thanks for the suggestions AM909. I tried with and without the -d[dsv] options. The values I'm using were obtained using the instructions in the readme for optimizing performance. I'll try with wider tcp port spacing.

The problem occurs both in the 500 MHz and 450 MHz bands, though I'll start tracking whether it's more prominent in the 450 MHz range.

I'm not using the -b-4 option for FMP24, but the window does show BW: 4 in the title. I'll give the tight filter a try.

I tried with and without auto-tune. With auto-tune enabled, the title shows just the frequency with no offset. When it does lock onto a a voice channel (auto-tune enabled or not), the spectrum display shows it spot on.

I'm not sure if it's coincidence, but just now I was missing a bunch of traffic and pressed Ctrl-C in the FMP24 window to stop it and try with different values. Instead of exiting, FMP24 went from idle to throwing up the last 4 frequencies that it missed and started tuning again.
 
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AM909

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FWIW, based on playing around with it just now, FMP24's auto-tune appears to require feedback to it from DSD+; otherwise, even with auto-tune enabled, it doesn't show any correction value after the freq and I don't think it actually does the auto-tuning.

I've also seen DSD+ go "deaf" at times, using it with SDR#, requiring a restart of DSD+ to get it to start decoding on the same CC that it previously refused to decode. Doesn't happen often enough to me to isolate.
 

Clear4Code7

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I've enabled extra CPU loading, although I don't believe I've been seeing drop outs. So far FMP24 indicates "idle" while the control channel log shows traffic.
 

AM909

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I'm only set up with one dongle at the moment (away from home), so I'm trying to monitor that system in 1R mode, where the SDR has to hop around to tune the voice channels and then come back to the CC.

I see that every time it tries to tune 506.65, the signal is weak and doesn't decode reliably. At that point, FMP24 just sits there on that channel for about 20 seconds, then DSD+ starts saying "Lost control channel, tuning to freq" where freq is sometimes (but not always) the CC. However, FMP24 doesn't react, and just stays on 506.65. It's console window doesn't show anything after "Tuning to 506.65". Latest instance was it tuned to 506.65 at 23:32:36, decoded nothing, and started trying to re-tune to 507.85 at 23:33:00.

If FMP24's divisions are 10dB, I get the CC and working voice channels about +25dB over the noise, while 506.65 is only about +10dB.
 

Clear4Code7

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Most the time I'm getting strong reception, though on occasion I do get weak voice channels. But even when the channel assignment is weak, shouldn't FMP24 at least attempt tuning to it?

I'm seeing the spectrum display remain blank and the console never displays the traffic message.

On a side note, is there a way to disable the log file output? I'd prefer not to constantly delete the file and it kind of nags on my conscience as it hammers my poor SSD.
 

slicerwizard

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On a side note, is there a way to disable the log file output? I'd prefer not to constantly delete the file and it kind of nags on my conscience as it hammers my poor SSD.
Are you referring to the console log? Just remove the >file or >>file stuff from whatever batch file you're running.
 
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