DSDPlus/V3 dongle Scan Problems

[marine61301]

I'm new to SDR and have been in it for about three months now, so this could be an issue that I created myself. I am running DSDPlus Fastlane with an RTL-SDR V3 dongle and scanning channels in the scanlist file. For the first couple minutes, I see the expected peaks and valleys in the spectrum display window (Top Picture), and I occasionally hear things. After running for a few minutes, I no longer see peaks/valleys as it changes channel. The line in the spectrum window stays near the bottom and I receive no audio when it does this (Bottom Picture). It seems that once the dongle is able to lock onto all of the frequencies (i.e. the "PLL NOT LOCKED" messages disappear) for some reason I lose reception. If I stop and restart scan, nothing changes. If I take the dongle out and reinsert it, I can see RF for a few minutes until we repeat the pattern. Anyone else experience this or know what is going on? I've deleted and reinstalled DSDplus on both my Windows and Ubuntu with the same results so I'm thinking maybe its the dongle?

 

[thewraith2008]

Not sure it's related, but your gain (@ 49.6) is very high. It looks like frontend overload.
I set my RTL-SDR V3 dongle to about 28. Of course this can be different as it can depend on antenna used.
Maybe overdriving the frontend is deafening the receiver after a time?

 

[slicerwizard]

RF gain is much too high and something is loose (RF connector, cold solder joint, ...)

If it was mine, I'd reflow the solder joints with a lighter.

 

[Ubbe]

If there's a way to change the scan speed to a lower rate, a higher mS time for each channel/frequency, then try that. Maybe the scan speed are too high and the PLL can't keep up with it and then loose the data connection between dongle and program. And as mentioned, the RTL-SDR dongle usually works best at around the 30dB gain value but can be different for different enviroment but the display indicate that it should be much lower than 49.6dB

/Ubbe

 

[slicerwizard]

You must have zero experience with FMP24...

 

[Ubbe]

Try running without scanning frequencies from your scanlist, Esc key are probably the one to use, and see if it runs in that mode. If the signals still disappears then it's probably the dongle in itself that have a problem. "PLL not locked" message could probably be related to the same issue. Could you install and run SDR# in windows and see if you have full reception at all times with that program?

/Ubbe

 

[simpilo]

Turn down your RF Gain pressing 'g'. You have it set so high it's imaging. Mine and other's dongles do the same thing. It is working normally. You only need enough gain to show peaks in the FFT on frequencies actually there. I also have observed that your first image is displaying a frequency not matching with the lower image. 3MHZ away probably will show nothing.

 

[marine61301]

Thanks all. I generally run the gain at about 28-32ish but I've turned it down to 7 and 0 and I'm still seeing the same issue. I'll have to open it up and see if maybe a solder joint is loose. It seems to be the dongle itself as I've swapped antennas and it happens with each one.

 

[marine61301]

Try running without scanning frequencies from your scanlist, Esc key are probably the one to use, and see if it runs in that mode. If the signals still disappears then it's probably the dongle in itself that have a problem. "PLL not locked" message could probably be related to the same issue. Could you install and run SDR# in windows and see if you have full reception at all times with that program?

/Ubbe

I have run SDR# and it seems to be operating normally when it's not continuously switching.

 

[simpilo]

Oh I totally forgot about the sma antenna connector in the RTL-SDR Blog V3 dongle has had quality issues with poor solder joints.

 

[marine61301]

Oh I totally forgot about the sma antenna connector in the RTL-SDR Blog V3 dongle has had quality issues with poor solder joints.

Thank you. I opened it up and all solder joints appear to be adequately done, especially around the SMA connector. I'm assuming that it's most likely a bad tuner. I can leave it on a single station and it works flawlessly. Scanning is a much different story.

 

[marine61301]

You must have zero experience with FMP24...

Would you like to elaborate or are you just here to criticize? Had you of read my post, you would have discovered that I am indeed new circa March 2019. Anything to add that is constructive?

 

[slicerwizard]

I referenced Ubbe's suggestion to change the scan speed in FMP24. There is no such option. FMP24 already scans very slowly.

 

[marine61301]

So after I opened it up to look at the solder connections and I noticed a "jumper" for lack of a better term, that is not shown on RTL-SDR.com in their image. It also looks like the solder is close enough to the GND from 3.3V that I can't tell if it's actually touching. Could this be part of my issue?

 

[thewraith2008]

Did you buy the from RTL-SDR.com?
Was that even in a case. There is also a dirty big cap right near the TCXO that looks like it would prevent that PCB even fitting inside the case.

 

[marine61301]

Did you buy the from RTL-SDR.com?
Was that even in a case. There is also a dirty big cap right near the TCXO that looks like it would prevent that PCB even fitting inside the case.

It does have a cover, however I think I might have gotten this off of Amazon rather than direct through their store. I didn't even notice the big part right next to the TCXO. Guess y'all helped me figure out my issue! Damn fakes.

 

[thewraith2008]

I don't think it's a fake but it's has been modified.
There is a mod there that is changing a 5v supply to some section to a 3.3v supply. i.e. The wire that goes from the 3.3v to cap.
The cap near the TCXO is for suppressing a sideband noise supposedly.

Some details about fixes to V3 (batch 1)
I don't thing yours is a batch one though.

 

[marine61301]

I don't think it's a fake but it's has been modified.
There is a mod there that is changing a 5v supply to some section to a 3.3v supply. i.e. The wire that goes from the 3.3v to cap.
The cap near the TCXO is for suppressing a sideband noise supposedly.

Some details about fixes to V3 (batch 1)
I don't thing yours is a batch one though.

Thank you for the information. I've just ordered a genuine one from the RTL-SDR.com site. I think I'll use this one as a learning experience and see if I can undo the mods that have been done to it.

 

[thewraith2008]

Your image is a bit dark but here is a screenshot of a slightly newer model RTL-SDR.com dongle (2018 9 13) for comparison.

Screenshot is from youtube video: "RTL-SDR.COM USB Dongle V.3. Is It Real Or Fake" - Fuzz The Pi Guy

 

[hamradionl]

marine61301
I dont know if this the case but:
When there is a MOD continuous put ON the BIAS and your antenna have a (shorted coil or other stub) to ground, than RTLSDR will turns it self OFF after some short time (as a protection short circuit). When you reconnected the RTLSDR to USB again, it reset itself and work again for short time and repeat this over and over.
Measure the SMA if there is 3.3 Volt present
After test, remove the BIAS MOD and it work...... as espected