DSDPlus Sync gets dropped receiving DMR from Openspot

[n5pwp]

I've been using DSDPlus 2p268. I have it setup to scan amateur radio DMR repeaters in my area. Everything seems to work fine. Then I added my OpenSpot's frequency and started having trouble when receiving traffic from it. In the middle of transmissions (usually over 10 secs or so) the audio drops off. I can look at FMP24's spectrum and the signal is still transmitting. I flipped on my TYT MD380 and the audio is still coming out of the radio. If I look at the 1RA window I see the DMR traffic has stopped and the last msg is "Sync: no sync". Sometimes it will pick back up a few seconds later but most times it doesn't sound again until someone else starts transmitting. I've read through the DSDPlus docs for FMP and DSDPlus and can find nothing that seems to address it. I have Googled the issue and read reports by others of seeing the same issue. But, with no solutions. I then tried an experiment and setup SDR# feeding DSDPlus and it has no problem. Audio comes out of DSDPlus as long as there is a transmission coming from the OpenSpot. I don't get the "Sync: no sync" msg until the transmission is done. This would seem to indicate to me that there is an issue with FMP24. I searched the forum here and no one else has reported it as far as I can see. Maybe no one is as goofy as I am and uses DSPlus to monitor their hot-spot when they have a radio that could do it. My goofiness aside, has anyone got any idea why FMP24 has an issue with sync from the Openspot? All of the DMR signals from the repeaters in my area don't seem to cause the problem so I'm thinking maybe there's just an incompatibility between FMP24 and OpenSpot. I am direct-connected from FMP24 to DSDPlus and I use a VB cable connection between SDR# and DSDPlus. If the DSDPlus FL folks need a raw recording when its doing this I can try to catch some of the traffic. Other than that I'm lost.

Here are my cmd lines for each situation.
FMP24 to DSDPlus:
Start CMD /c "FMP24 -i2 -o20002 -f434.025 -_3 &"
Start CMD /c "DSDPlus -fa -rv -i20002 -T -wel60.50 -wes400.1000 -weh18 -wch18 -_11 &"

SDR# to DSDPlus
dsdplus -i2 -fr -rv &

Thanks for any insight.
Mike

 

[KE5MC]

I don't have a solution, but maybe something to try help understand the dropout.

Receiving repeaters is fine, but OpenSpot has dropped sync, just to clarify. Two differences that come to mind between the two is the signal strength and quality. Signal quality not a variable that can be controlled. However the strength strength out of the OpenSpot might be. I have a Zumspot at 10mW and it surprises me how far I can walk down the street with my HT and it still works. I believe the OpenSpot has a higher output. I would try reducing the output of the OpenSpot or removing the antenna of the receiver you are using for FMP24/SDR#. Which receiver are you using? Not likely to matter, but could. Another thought along the signal strength idea is the gain control of the receiver is better with SDR# than FMP24 if strong received signal is the issue.

One thing I have learned over the years is how dynamic the measured received signal strength can be. In most situation the tools to measure are not available so we work in the dark and in the analog world that usually is OK. In this case I suspect until proven that a SDR receiver with less that the best frontend and OpenSpot transmitting in close proximity might lead to 'problems'.

Actually as I finish this post I am wonder if the OpenSpot output frequency is what it saids it is or drifts after it starts transmitting. Something so small as not to be noticed except by DSDPlus. I would put that in the signal quality category.

Good Luck!
Mike

 

[n5pwp]

Mike
Yes, you've got it. Repeaters are ok. The OpenSpot connection is the one that is problematic. I have also noticed that when I use FMP24 as the tuner it doesn't always pop-up the entry in the Channel Activity window. If I use SDR# it always populates. I too have been amazed by how the small amount of output power from the OpenSpot covers a large area. Currently I'm operating at 0.5mw. I have taken it to the lowest level thinking I might be overloading the RTL-SDR's front end. I have gone all the way down to 0.03mw and it still is a strong signal. I have lowered the gain setting in FMP24 as well. It still seems to have the issue. The SDR I'm using is a NESDR SmarT. It has a txco and the ppm is right around 0. At first I thought the OpenSpot was actually dropping the sync signal but it is locked in on my HT. Plus SDR# seems to hold on just fine too. I could try another SDR. I have a couple of RTL-SDR V3s here too.

Another thing to try is the configuration for FMP24. I'm currently direct-linked FMP24 to DSDPlus. I was going to try using TCP linking. I've read some issues are better handled using TCP linking rather than direct-linking. I'm not sure what underlies the two different methods, but I can try it and if it fixes it I can rationalize it later.

I like how lightweight FMP24 is on the system but I think it might either be too under-powered or not have the resilience of SDR# or the tuner in my HT.

Thanks for your reply, Mike.

 

[slicerwizard]

What's different about your hotspot signal vs DMR repeaters? Just power levels? Does the hotspot transmit both DMR timeslots or does it TDMA pulse like a user radio does? Does disabling squelch in FMP24 have any effect?

 

[n5pwp]

slicerwizard:
The OpenSpot only transmits one TS in its default hotsport mode. The docs say it can be configured to be a base station or mobile using both TS. I think Brandmesiter handles outputting all traffic on one TS so that is not an issue. I've turned off SQ on FMP24 and it made no difference. As far as power is concerned the OpenSpot will output upto 19.95 mW. I have brought it all the way down to 0.03mW. Normally I run about 0,5 mW. It doesn't seem to make a difference. The antenna is a dual-band (2M/70cm) Comet up on the roof. I have been running the last several days on SDR# using the Frequency Scanner plugin and it has been working perfectly. I would say I have probably found my solution. I will check back with the FMP24 in the FL release as they come out to see if it has been fixed as new releases come out. I guess my use case is a niche so probably not a priority for the FL guys to focus on. Thank you to everybody that chimed in. I appreciate the help.
73
n5pwp (mike)