DSDPlus DSDPlus FastLane Not Holding on P25 Control Channel

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KM4BLG

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Hi all,

Currently running DSDPlus Fast Lane on Windows 10, with a pair of RTL-SDR dongles. Here we have 3 P25 systems: city, county, and state. For the county and state systems, everything decodes fine. Start the software and it's off and rolling; either with using both, or just one of them. For the city system however, I have an interesting issue:

When I first start the software, it just sits there. It doesn't appear to be decoding anything. Then, it will start decoding for a few seconds, stops decoding and starts going "Lost control channel, tuning to xxx.xxxxx" over and over. When it cycles back around to the actual control channel, it will decode for as long as it's over there, but it continues to scan. Every once in a while, it will stabilize and start working again, but then it kicks off into the same cycle again. This continues for about 10-30 minutes, until it finally locks in and stays decoding 100% of the time. If I close the software and re-open it, the process starts all over again.

I know that it is not an antenna/radio issue, because I can see their tower out the window. Even with the antenna unplugged, the signal strength is well above the top of the spectrum graph. Plus, I have similar signals on the other 2 systems, including one of them even sharing the same tower. I have reduced the gain, so that it falls back down into the range of the graph, thinking it was overloading the receiver. It almost acts like the receiver is drifting and then finally warms up, however the signal is perfectly within the bandwidth of the receiver on the spectrum graph.

It's very frustrating because if there is something that I want to quickly tune in and listen to, I have to wait until it stabilizes, or leave it running all the time and just mute it when not listening.

Any ideas?
 

a417

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I know that it is not an antenna/radio issue, because I can see their tower out the window.
Oh yeah?
Even with the antenna unplugged, the signal strength is well above the top of the spectrum graph. Plus, I have similar signals on the other 2 systems, including one of them even sharing the same tower. I have reduced the gain, so that it falls back down into the range of the graph, thinking it was overloading the receiver. It almost acts like the receiver is drifting and then finally warms up, however the signal is perfectly within the bandwidth of the receiver on the spectrum graph.
You're overloading the receiver.

Everything that concerns me is in the first sentence. Read what you wrote.

without the antenna the signal is above the top of the spectrum graph.

Put the antenna on and turn the gain WAY THE HELL DOWN.

are they temperature controlled oscillator dongles? Cheapo ones do drift, doing precisely what you are describing. Get better dongles or deal with the innaccuracy.
 

KM4BLG

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Oh yeah?

You're overloading the receiver.

Everything that concerns me is in the first sentence. Read what you wrote.

without the antenna the signal is above the top of the spectrum graph.

Put the antenna on and turn the gain WAY THE HELL DOWN.

are they temperature controlled oscillator dongles? Cheapo ones do drift, doing precisely what you are describing. Get better dongles or deal with the innaccuracy.
I have already turned the gain way down...I have attached a graph of my spectrum. Is this still too strong?
cc.JPG
 

a417

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The spike on the left is the signal, the green is expanded view. Notice they are at different peaks. I wish I had that kind of signal at a gain of 8.7. You are right next door to a flamethrower, you are lucky.

what kind of dongles do you use, are they temperature controlled oscillator ones?
 

slicerwizard

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Toronto, Ontario
When I first start the software, it just sits there. It doesn't appear to be decoding anything. Then, it will start decoding for a few seconds, stops decoding and starts going "Lost control channel, tuning to xxx.xxxxx" over and over. When it cycles back around to the actual control channel, it will decode for as long as it's over there, but it continues to scan. Every once in a while, it will stabilize and start working again, but then it kicks off into the same cycle again. This continues for about 10-30 minutes, until it finally locks in and stays decoding 100% of the time. If I close the software and re-open it, the process starts all over again.
You need to pay particular attention to the P25 CC decoding in the DSD+ console window. Is it less than perfect? Does it stop / drop to near-zero OSPs decoded? If it does, why? What's happening in the FMP24 spectrum window? What's happening in the DSD+ source audio window?
 

KM4BLG

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I have turned my gain all the way down to 3.7 and it's still that strong. The console window completely stops putting out anything when it quits decoding. It just sits there in an idle state. When it is successfully decoding, the console is spamming so fast I can't really read it.
 
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