Troubleshooting/optimizing decoding using DSDPlus Fast Lane

[alpharaysmax]

I've got a basic setup running to monitor a local P25 system, using FMP24 and DSDPlus Fast Lane and an old (circa 2013) Nooelec RTL-SDR dongle. My computer is a 2019 16" MacBook Pro running Windows 10 in Parallels. CPU and memory utilization are both low, so I don't think the computer is an issue. The antenna is a multi-band scanner antenna located on the roof and connected via 25 feet of RG-6 coax.

It works, but the decode is consistently very choppy, making it very difficult to understand, so I'm trying to figure out how to troubleshoot this.

I also have an SDS100 and have no issues receiving and properly decoding the voice channels when connected to the same antenna. So I'm assuming my issue is either with the RTL hardware or my FMP24/DSD+ settings.

Is it worth upgrading to a new RTL dongle? I'm guessing the answer is "yes", just because the one I have is now seven years old and would help rule in/out the hardware as an issue.

Otherwise, what else should I check or experiment with? All of this is a bit new (again) to me; messed with it a bit years ago but am just getting back into it now and am a bit lost in the endless options and tweaking.

FMP24 settings:

PPM correction: 33.0 (calibrated manually using SDR# and a known FM signal)
Gain: 14.5 dBm
Vol: 100
Bandwidth: 12.5 kHz

DSD+ console reports lots of "CRC FAIL" and errors; for example:

2020.07.23 13:53:40 Opcode=5 MFID=90 85 90 40 80 80 00 00 00 00 00
2020.07.23 13:53:40 Sync:+P25p1 NAC:8A2 PDU CRC FAIL
2020.07.23 13:53:41 Sync:+P25p1 NAC:8A2 TDU
2020.07.23 13:53:41 Sync:+P25p1 NAC:8A2 TSDU SYNC_BCST US=0 IST=1 MMU=0 MC=0 VL=0 LTO=-5h 2020/07/23 17:53 uSlot=5170
2020.07.23 13:53:41 MOT_BSI_GRANT Null BSI ch=161.085
2020.07.23 13:53:41 IDEN_UP_TDMA ID=9 Base=160. Offset=+0 Spacing=2.5 BW=12.5 Slots=2
2020.07.23 13:53:41 Sync:+P25p1 NAC:8A2 TSDU SCCB_EXP RFSS=1 Site=2 TXch=160.965 RXch=158.895
2020.07.23 13:53:41 IDEN_UP_VU ID=4 Base=150. Offset=+0 Spacing=2.5 BW=12.5
2020.07.23 13:53:41 Opcode=9 MFID=90 89 90 0B 40 00 00 00 00 00 00
2020.07.23 13:53:41 Sync:+P25p1 NAC:8A2 PDU CRC FAIL
2020.07.23 13:53:41 Sync:+P25p1 NAC:8A2 PDU CRC FAIL NET_STS_BCST
2020.07.23 13:53:41 Sync:+P25p1 unknown/invalid DUID: 2
2020.07.23 13:53:41 Sync:+P25p1 NAC:8A2 TSDU IDEN_UP_TDMA ID=6 Base=150. Offset=+0 Spacing=2.5 BW=12.5 Slots=2
2020.07.23 13:53:41 ERR6 SCCB_EXP RFSS=1 Site=2 TXch=154.1675 RXch=158.865
2020.07.23 13:53:41 CRC FAIL
2020.07.23 13:53:41 Sync:+P25p1 NAC:8A2 PDU ERR11 RFSS_STS_BCST SysID=8A5 LRA=0 RFSS=1 Site=2 CCTX=161.085 CCRX=158.925 SC=60
2020.07.23 13:53:41 Sync:+P25p1 TDU
2020.07.23 13:53:41 Sync:+P25p1 TSDU ERR3 SYNC_BCST US=0 IST=1 MMU=0 MC=0 VL=0 LTO=-5h 2020/07/23 17:53 uSlot=5250
2020.07.23 13:53:41 ERR9 IDEN_UP_VU ID=4 Base=150. Offset=+0 Spacing=2.5 BW=12.5
2020.07.23 13:53:41 ERR9 SCCB_EXP RFSS=1 Site=2 TXch=160.965 RXch=158.895
2020.07.23 13:53:41 Sync:+P25p1 NAC:8A2 PDU CRC FAIL
2020.07.23 13:53:41 Sync:+P25p1 NAC:8A2 TDU
2020.07.23 13:53:41 Sync:+P25p1 NAC:8A2 TSDU CRC FAIL
2020.07.23 13:53:41 CRC FAIL
2020.07.23 13:53:41 CRC FAIL
2020.07.23 13:53:41 Sync:+P25p1 NAC:8A2 PDU CRC FAIL
2020.07.23 13:53:41 Sync:+P25p1 NAC:8A2 TDU
2020.07.23 13:53:41 Sync:+P25p1 NAC:8A2 TSDU IDEN_UP_TDMA ID=7 Base=155. Offset=+0 Spacing=2.5 BW=12.5 Slots=2
2020.07.23 13:53:42 SCCB_EXP RFSS=1 Site=2 TXch=154.1675 RXch=158.865
2020.07.23 13:53:42 IDEN_UP_TDMA ID=9 Base=160. Offset=+0 Spacing=2.5 BW=12.5 Slots=2
2020.07.23 13:53:42 Sync:+P25p1 NAC:8A2 PDU ERR4 NET_STS_BCST WACN ID=BEE00 SysID=8A5 LRA=0 CCTX=161.085 CCRX=158.925 SC=60
2020.07.23 13:53:42 Sync:+P25p1 NAC:8A2 TDU
2020.07.23 13:53:42 Sync:+P25p1 NAC:8A2 TSDU Opcode=9 MFID=90 09 90 0B 40 00 00 00 00 00 00
2020.07.23 13:53:42 IDEN_UP_VU ID=4 Base=150. Offset=+0 Spacing=2.5 BW=12.5
2020.07.23 13:53:42 Opcode=5 MFID=90 85 90 40 80 80 00 00 00 00 00
2020.07.23 13:53:42 Sync:+P25p1 NAC:8A2 TSDU SYNC_BCST US=0 IST=1 MMU=0 MC=0 VL=0 LTO=-5h 2020/07/23 17:53 uSlot=5330
2020.07.23 13:53:42 IDEN_UP_VU ID=5 Base=160. Offset=+0 Spacing=2.5 BW=12.5
2020.07.23 13:53:42 SCCB_EXP RFSS=1 Site=2 TXch=160.965 RXch=158.895
2020.07.23 13:53:42 Sync:+P25p1 NAC:8A2 PDU RFSS_STS_BCST SysID=8A5 LRA=0 RFSS=1 Site=2 CCTX=161.085 CCRX=158.925 SC=60
2020.07.23 13:53:42 Sync:+P25p1 NAC:8A2 TDU
2020.07.23 13:53:42 Sync:+P25p1 NAC:8A2 TSDU CRC FAIL
2020.07.23 13:53:42 CRC FAIL
2020.07.23 13:53:42 CRC FAIL

 

[Forts]

Assuming your signal is good, try setting the bandwidth to 9.5 in FMP24. Also make sure your gain setting is good... too much signal can be just as bad as too little. Also, since it's an older dongle make sure your dongle is correctly on frequency using the - & + PPM corrections. Beyond that, it could be something weird with running it on a Mac. Perhaps another Mac user will chime in with their results.

 

[rlmurray56]

Running in a VM is never a good idea. I know. I have tried. There are tons of threads here about exactly that and all the problems it causes. You should always try use something that is native to your operating system. If you are only wanting P25, have you tried SDRTrunk ? It is cross platform and runs natively on a Mac. I am running it here, problem free. There is also a Google Groups support forum where the developer and others will answer questions.

 

[alpharaysmax]

Wow, thank you! I've never used SDRTrunk before. The setup was much simpler and it actually seems to be working "out of the box" on my Mac.

Unless I'm mistaken, it does seem that I need to pick up a second tuner to have one dedicated to the control channel and one to the voice channels. I did come across a tutorial for using a single tuner if the frequencies covered are within the bandwidth of the tuner, but here's too much spread for that in my case.

That said, I manually tuned to a voice channel for a while to pick up a few transmissions to verify that the P25 decoding worked well and it does — no skips or stutters like the FMP24/DSD+ setup. I was able to get that configuration working better with Forts's suggestions (thanks!) but it still wasn't quite as clear as it should be.

But I think this will work well — just ordered a second tuner and the other components needed to get everything hooked up!

 

[jets1961]

Out of curiosity what type of system is it Harris or Motorola?

 

[rlmurray56]

Wow, thank you! I've never used SDRTrunk before. The setup was much simpler and it actually seems to be working "out of the box" on my Mac.

Unless I'm mistaken, it does seem that I need to pick up a second tuner to have one dedicated to the control channel and one to the voice channels. I did come across a tutorial for using a single tuner if the frequencies covered are within the bandwidth of the tuner, but here's too much spread for that in my case.

That said, I manually tuned to a voice channel for a while to pick up a few transmissions to verify that the P25 decoding worked well and it does — no skips or stutters like the FMP24/DSD+ setup. I was able to get that configuration working better with Forts's suggestions (thanks!) but it still wasn't quite as clear as it should be.

But I think this will work well — just ordered a second tuner and the other components needed to get everything hooked up!

No, you only need to set up your channel in the playlist editor for the control channel frequency of the system you are trying to monitor. , SDRTrunk will follow the P25 trunking, even with a single dongle. Don't enter individual voice frequencies. And, if you do nothing else, read the documentation on the GitHub page, it will answer 99% of your questions.