SDS100/SDS200: SDS200: Site issue with NXDN reception with debug info

[devicelab]

SDS200 with a multiple-site NXDN RAN trunk system. I've avoided all other sites for the time being. I'm having an issue with a site that's very close to my QTH. It's not overloaded but it is very strong. Oddly, the other sites decode fine. The programming data is correct and has been confirmed.

This site/system seems to work best with the filter OFF. I've tried NORMAL & AUTO as well.

Issues I'm seeing:

1. RSSI meter is blank despite low noise values and decode info (and site location)
2. Noise values go crazy if I use alternate filters but are low & stable with filter OFF
3. With voice traffic, the RSSI meter works normal
4. Virtually no D-ERROR values being reported (may hit 5 at random times)

See picture for reference of what it looks like when waiting for voice traffic. Log file attached. Collected enough data with voice channel traffic.

Again, this problem seems isolated to just this site.

Debug log --> https://www.dropbox.com/scl/fi/13dl...751.zip?rlkey=do6x1eb35aaa8k9mn90cbsta4&raw=1

 

[n1chu]

Did you try attenuating the strong system?

 

[devicelab]

Did you try attenuating the strong system?

Yes just using the ATT option in the Site. It didn't have any effect other than to reduce the signal.

FWIW, even though it's a close site, it's not super strong. My Airspy shows it well but it's not like other systems/sites in my area where it nearly overloads my Airspy.

 

[n1chu]

Maybe the only solution is to dedicate one receiver to that strong system and another to everything else?

 

[Ubbe]

Your debug log show that you get some interference and the CRC data errors starts to happen and then the decode stops completely. It's often a 0.3 to 0.5 sec long interference that could be idle burst transmissions, from a DMR system, and when they do a voice call you are blocked for a longer time. If you have the waterfall feature installed it would be a good use of it to see if you have any short 0.5 sec peaks in the frequency band.

Try to always use the attenuator and try all different filters and then do IFX to the systems frequencies, 461.1125 461.700 461.850 463.2250 463.275 and try the filters one more time. It seems to be only the 461MHz frequencies that are interfered and need to be fixed?
You can do Channel+frequency+Channel and then do Function+7 to toggle IFX and then continue scan again.

RSSI values will only show if the squelch detects a carrier and then opens. You can set squelch to 0 to always read RSSI values if only scanning digital systems, as it will slow down scanning speed, but as a hold time for a trunked system are always a minimum of 1,5 sec it will not matter much.

Noise are anything that isn't a dead quiet carrier, so any data signal will be regarded as noise so isn't useful to look at for digital systems.

/Ubbe

 

[devicelab]

Your debug log show that you get some interference and the CRC data errors starts to happen and then the decode stops completely. It's often a 0.3 to 0.5 sec long interference that could be idle burst transmissions, from a DMR system, and when they do a voice call you are blocked for a longer time.

No, I don't have the WF feature. I have an Airspy for that.

Okay, so I have a Tier DMR CC on 460.95 that may be causing the interference you're talking about. I don't see this on the Airspy however. I'll pay attention to SDR# and see what is going on around the CC frequency.

EDIT: Looking at the Airspy now, the 460.95 signal shows splatter 100khz on each side. It's not quite enough to reach the 461.125 signal from the Site 31 above. It must be some DMR voice channel that's popping up.

This area has massive DMR so it's not unheard of to have digital on top of digital or directly next to each other. (And since DMR & NXDN use channel spacing they can get rather close.)

 

[devicelab]

RSSI values will only show if the squelch detects a carrier and then opens. You can set squelch to 0 to always read RSSI values if only scanning digital systems, as it will slow down scanning speed, but as a hold time for a trunked system are always a minimum of 1,5 sec it will not matter much.

Okay but why do the other CC sites show the RSSI meter when cycling through the various sites? For whatever reason, this site's meter rarely ever shows up. It shows up during voice traffic but not when just scanning the sites. (In the above case, I've locked out the other sites.)

 

[Ubbe]

With squelch open it should always show RSSI. If the signal are so weak that it is below what can be received, something like -120dBm, it doesn't show any value, just dashes. But also when it encounter interference it can stop working. I have also seen that when receiving analog signals, although being weak but still can be monitored, it sometimes just show dashes.

SDS scanners has a lot of internal signals in its receiver chip that mix with received signals and creates additional frequencies from the received ones. So do not only check nearby frequencies as the interference can come from several MHz away. Interference test SDS100

/Ubbe

 

[dave3825]

If you have the waterfall feature installed it would be a good use of it to see if you have any short 0.5 sec peaks in the frequency band.

No, I don't have the WF feature. I have an Airspy for that.

If you scanner is experiencing and kind of internal interference, the Airspy most likely won't show it.