I own an RTL-SDR v3 USB dongle (official version from rtl-sdr.com). I've successfully used it for decoding weather satellites past year. I use (GQRX + Audacity)/(Arch Linux 64bit) + (WXtoIMG)/(Windows 10 64bit) combination to receive and decode NOAA images and (glrpt)/(Arch Linux 64bit) to receive and decode images from Meteor-M sats. However now I observe strange behavior. I've tried to record about a dozen of NOAA passes but with no luck - my images are slanted and WXtoIMG can't do anything with that (see picture below). Also it says that it can't find telemetry data or complains about poor SNR ratio. This is strange because I constantly get about 40 dB SNR in GQRX for most prominent APT peaks.
glrpt I observe issue with PLL locking. Signal level is awesome, AGC works fine, but PLL never locks even if satellite is flying right above my head. Previous summer I was able to start decoding from 2--4 degrees above the horizon.
At the same time I use GQRX quite well and can clearly hear FM broadcasting, NFM chatting and even AM broadcasting with the use of SpyVerter upconverter.
I don't know what can cause such issues as non-lockable PLL and troubles with NOAA reception (I think they are related to each other). I suppose my dongle become damaged somehow but don't know exactly how. It has protection diode on the input and I handle it with care so it shouldn't be ESD-smashed (I suppose it will not work at all after discharge).
May be someone has already faced such a problem and could give me some advice? Or how can I test my hypothesis on 3rd-party test?
I've tried with using LTS 5.4.32 kernel on Arch Linux, compiling
glrpt with GCC 8.4.0, clang but still getting the same issue. WXtoIMG works fine - when I feed old recording to it then it gives me nice images. Moreover, I've found that its is impossible to decode DRM HF stations with DReaM decoder in realtime at all - it fails to get all three CRCs good. Only sometimes it's able to say me station name and show list of channels. At the same time feeding sample audio from other users works just fine. I suppose it's all related to the dongle - APT, LRPT, DRM fails while simple audio works fine.
UPDATE 2: I've analyzed audio spectra for two files: good recording from last year and a bad one from past week. Here are the results.
Good. I can see main 2.4 kHz peak, 4.8 kHz multiple and minor peaks. Frequency drift @2400 Hz is negligible.
Bad. There is no multiple of 4.8 KHz, main peak is very broad. I can't see minor frequencies. Also there is a quite significant drift from 2400 Hz.
UPDATE 3: Yesterday I got another dongle (simple blue from AliExpress). The problem is still here! I observe the same symptoms as with RTL SDR blog v3 dongle. Even spectra are the same.
UPDATE 4: I've found the cause of the problem - it's VOLK who ruined decoding. Filed an issue on GQRX GitHub. Seems like there are some serious bugs with VOLK's DSP, will recheck soon.
Also both dongles - cheap "blue Chinese" and RTL SDR v3 works just fine! So there is definitely no problem with crystals inside them.
UPDATE 5: I've investigated the problem even further and this is not a bug with a VOLK. GQRX's frequency correction seems to ruin decoding. See my answer for full details.