SDR Newbie questions

[RTmed519]

This is quite a long story, but I thought I'd give it a go in case anyone has any suggestions. I've been using the RTL-SDR dongle (quite a few of them, actually) for a number of months now (late last year), with very few problems. I recently moved into a new place, got everything hooked up, and noticed a few things.

Initially, it works great. After having the SDR plugged in for about 3-4 hours, it starts to lose the control channel frequently, but doesn't have a problem getting it back. After about 6 hours, it has a hard time getting the control frequency at all. This is an apartment building with a lot of interference, which I assume plays a big part.

I've swapped the dongle with 4 different ones, to no avail. I've used those same dongles in different locations, on trips, etc with few issues. My guess is the interference is causing strain on the dongle somehow.

Does anyone else have these issues, or know what the problem might be or how to fix it?

(I use this on an 800mhz P25 P1 system)

 

[SteveSimpkin]

Do they all of the RTL-SDR dongles exhibit the same symptom of working ok for a few hours and then malfunctioning? It almost sounds like they are overheating. I know my RTL-SDR dongle would get very warm after an hour or so. These models have a metal case that acts as a heat sink. Make sure they have plenty of open space around them to help get rid of the heat. If they are still running hot see if you can place a fan near them to help dissipate the heat.

 

[RTmed519]

Do they all of the RTL-SDR dongles exhibit the same symptom of working ok for a few hours and then malfunctioning? It almost sounds like they are overheating. I know my RTL-SDR dongle would get very warm after an hour or so. These models have a metal case that acts as a heat sink. Make sure they have plenty of open space around them to help get rid of the heat. If they are still running hot see if you can place a fan near them to help dissipate the heat.

All of them do, yes. My only problem with said theory (which sounds like it should be the case) is that I didn’t have this problem before moving. I moved into an area with a lot of WiFi boxes, and I’d assume other things causing interference.

 

[SteveSimpkin]

All of them do, yes. My only problem with said theory (which sounds like it should be the case) is that I didn’t have this problem before moving. I moved into an area with a lot of WiFi boxes, and I’d assume other things causing interference.

If it was interference from equipment nearby that was already on, I would expect the problem to appear immediately when you started the RTL-SDR, not after a set amount of time. I believe the dongles use the same amount of power when they are running regardless of any interference nearby.

 

[RTmed519]

If it was interference from equipment nearby that was already on, I would expect the problem to appear immediately when you started the RTL-SDR, not after a set amount of time. I believe the dongles use the same amount of power when they are running regardless of any interference nearby.

I’ll have to do some fumbling around with it and see if I can figure it out. It very well could be the overheating.

 

[Carter911]

I am still a newbie with SDRs, but:

Are you running OP25 for your system, and the original version or Boatbod's version?
Boatbod's version has a "fine tuning" option, (it adds the -d xxx parameter, not just the -q xxx parameter).
I have several RTL-SDRs.
One exhibited similar problems.
I performed the tuning setup when I initially set it up, and it worked for several hours, but then it would stop playing the audio.
When I went back and "fine tuned" it a little better it solved the problem.
Tuning was accomplished first by watching the talk group activity on the display when course tuning, and then by watching the "eye pattern" for the best +/- 3 level, (i.e. not too high or too low).
Then I updated the tuning parameters in the command line scripts.

JC

Edit:
I also have a heat sink placed on both the top and the bottom of the dongles, to help them run cooler.
Heat, in this case, wasn't the problem, however.

 

[Sparky_ND]

If the dongles don't have txco's they may be drifting off frequency. Check a local weather radio channel after the dongle is thoroughly warmed up to see if the peak is centered on frequency, if not, adjust it with the ppm correction.

 

[RTmed519]

I am still a newbie with SDRs, but:

Are you running OP25 for your system, and the original version or Boatbod's version?
Boatbod's version has a "fine tuning" option, (it adds the -d xxx parameter, not just the -q xxx parameter).
I have several RTL-SDRs.
One exhibited similar problems.
I performed the tuning setup when I initially set it up, and it worked for several hours, but then it would stop playing the audio.
When I went back and "fine tuned" it a little better it solved the problem.
Tuning was accomplished first by watching the talk group activity on the display when course tuning, and then by watching the "eye pattern" for the best +/- 3 level, (i.e. not too high or too low).
Then I updated the tuning parameters in the command line scripts.

JC

Edit:
I also have a heat sink placed on both the top and the bottom of the dongles, to help them run cooler.
Heat, in this case, wasn't the problem, however.

I’ve been running SDR Trunk, due to it being available on windows, and saving every transmission (not the entire call). The extra heat sink isn’t a bad idea.

 

[RTmed519]

If the dongles don't have txco's they may be drifting off frequency. Check a local weather radio channel after the dongle is thoroughly warmed up to see if the peak is centered on frequency, if not, adjust it with the ppm correction.

Good idea. I’ll try this!

 

[AM909]

If the dongles don't have txco's they may be drifting off frequency. Check a local weather radio channel after the dongle is thoroughly warmed up to see if the peak is centered on frequency, if not, adjust it with the ppm correction.

I haven't found weather channels (in SoCal) to be very good calibration sources. In the US, by regulation (47 CFR 90.213), 930 MHz trunking base stations require 0.1 ppm stability (i.e. < 100 Hz) and make good calibration sources IME.