Some R820T RTLSDR need digital AGC set

[Isa001]

Hi,

I'm unable to work with RTL_433 last release (21.05) on my RPi 3 + RTL-SDR R820T
Compilation & Installation are ok.

But unfortunately decoding is not working.

root@romeo:~# rtl_433 -g 43.4 -p 84 -f 433920000 -F kv -a 4 -vvv
rtl_433 version 21.05 (2020-05-09) inputs file rtl_tcp RTL-SDR with TLS
Use -h for usage help and see https://triq.org/ for documentation.
Trying conf file at "rtl_433.conf"...
Trying conf file at "/root/.config/rtl_433/rtl_433.conf"...
Trying conf file at "/usr/local/etc/rtl_433/rtl_433.conf"...
Trying conf file at "/etc/rtl_433/rtl_433.conf"...
Registered 157 out of 186 device decoding protocols [ 1-4 8 11-12 15-17 19-23 25-26 29-36 38-60 63 67-71 73-100 102-105 108-116 119 121 124-128 130-149 151-161 163-168 170-175 177-186 ]
Found Rafael Micro R820T tuner
Exact sample rate is: 250000.000414 Hz
[R82XX] PLL not locked!
Sample rate set to 250000 S/s.
Tuner gain set to Auto.
Tuned to 433.920MHz.
Allocating 15 zero-copy buffers
baseband_demod_FM: low pass filter for 250000 Hz at cutoff 25000 Hz, 40.0 us

RTL_433 running for many hours but never decodes anything.
Others scripts utilities RF decode work fine with the same setup (RPI + R820T + antenna)
When monitoring +/- 433.92 Mhz, I can see many signals. For sure the reception is ok but no decoding
RPi is not overloaded, I tried to limit to some known protocols with -R without any success.

What's wrong ?? Only RTL_433 doesn't work on my RPI !!

For info, I also have exactly the same problem with Windows 10
I use the same usb RTL-SDR R820 with rtl_433_64bit_static.exe => no decode, nothing decoded after many hours.

My R820T with SdrSharp works fine. I can monitoring the band. Many activities on 433.92 with clear signals

R820T + SdrSharp + RTL_433 plugin work fine. I decode many devices. This setup proves that the reception is ok.

Impossible to run RTL_433 stand alone on my RPi 3 or Windows 10 with my RTL-SDR R820T

Thanks in advance for your help

[merbanan]

Try adjusting the frequency. Most likely some stationary disturbance.

[Isa001]

Thanks for fast reply.

I already tried many different parameters, frequencies, samplerate, ........ but no success.
Very strange behaviour with RTL_433.
Not even a trace or something in the console in verbose mode.
What's happen during the decoding process ?? no trace, no debug display
Very frustrated because I have only a problem with this script RTL_433.
All others script I use for RF decode work with the same setup (RPi 3 + R820T)

It seems that the script freezes. That's just a supposition.

[zuckschwerdt]

Try -A to see if/what data comes in, and try -vvv to see if/which decoders get triggered.

[Isa001]

Running for 10 minutes, but no data decoded, no trace displayed .
Usually datas are sent every +/-30sec

root@romeo:~# rtl_433 -A -vvv -p 84 -f 433925000
rtl_433 version 21.05 (2020-05-09) inputs file rtl_tcp RTL-SDR with TLS
Use -h for usage help and see https://triq.org/ for documentation.
Trying conf file at "rtl_433.conf"...
Trying conf file at "/root/.config/rtl_433/rtl_433.conf"...
Trying conf file at "/usr/local/etc/rtl_433/rtl_433.conf"...
Trying conf file at "/etc/rtl_433/rtl_433.conf"...
Registering protocol [1] "Silvercrest Remote Control"
..
Registering protocol [186] "Hyundai TPMS (VDO)"
Registered 157 out of 186 device decoding protocols
Found 1 device(s)

trying device  0:  Realtek, RTL2838UHIDIR, SN: 00000102
Found Rafael Micro R820T tuner
Using device 0: Generic RTL2832U OEM
Exact sample rate is: 250000.000414 Hz
[R82XX] PLL not locked!
Sample rate set to 250000 S/s.
Bit detection level set to 0.0 (Auto).
Tuner gain set to Auto.
Frequency correction set to 84 ppm.
Reading samples in async mode...
Tuned to 433.925MHz.
Allocating 15 zero-copy buffers
baseband_demod_FM: low pass filter for 250000 Hz at cutoff 25000 Hz, 40.0 us

[zuckschwerdt]

Strange. Since there is a watchdog looking for input stall, there must be I/Q data coming in. It would have to be blank though.
Can you record a short sample with rtl_433 -p 84 -f 433.925M -w test_433.925M_250k.cu8 -T 10 and post as zip here?

[Isa001]

That's what I got with:
rtl_433 -p 84 -f 433.925M -w test_433.925M_250k.cu8 -T 10

test_433.925M_250k.zip

[Isa001]

Another one with an other R820T
rtl_433 -p 50 -f 433.920M -w test_433.920M_250k.cu8 -T 10

test_433.920M_250k.zip

[zuckschwerdt]

Drop the cu8 on https://triq.org/pdv/ to see the spectrum content. The first file is blank, the second has a partial transmission, but too weak to demod. Looks like just bad reception or to low gain (which auto-gain should take care of in hardware though).

[Isa001]

Thanks for your help and the explanations.

I had done several test with cu8 files and the spectrum app.
Most of files are blank or only 1 or 2 weak signals.

At a glance, the spectrum doesn't represents what I'm able to receive on 433.92.
Now I understand why rtl_433 doesn't decode anything.

When I monitoring this frequency (sdrsharp & R820T on Windows 10), there is a lot of traffic with many strong signals.

I'm sure 433.92 is very active in my area

Could I conclude my RTL-SDR is not tuned to 433.92 by RTL433 ??
Maybe add a tempo before the decode process could help to ensure the right tune for old RTL-SDR key.

[merbanan]

Try with a fixed gain (-g 50 or so). It might be broken hardware.

[Isa001]

root@romeo:/home# rtl_test
Found 1 device(s):
  0:  Realtek, RTL2838UHIDIR, SN: 00000102

Using device 0: Generic RTL2832U OEM
Found Rafael Micro R820T tuner
Supported gain values (29): 0.0 0.9 1.4 2.7 3.7 7.7 8.7 12.5 14.4 15.7 16.6 19.7 20.7 22.9 25.4 28.0 29.7 32.8 33.8 36.4 37.2 38.6 40.2 42.1 43.4 43.9 44.5 48.0 49.6
[R82XX] PLL not locked!
Sampling at 2048000 S/s.

I had already tried with different fixed gain, without success.

I think my R820T is no tuned to 433.92. Why ?

[merbanan]

Well to confirm that you need a controllable signal. Try with some car keys or a door bell. Those should be possible to observe in the spectrum.

[Isa001]

Wrong conclusion, my R820T is on the right frequency.
I see the signal of my remote control door bell with cu8 file recorded.

[zuckschwerdt]

Our eyes are a lot better to make out signals than the demodulator. You need to have some red color (maximum signal strength) in the signal for rtl_433 to pick up anything. Perhaps compare to a few good signals from https://github.com/merbanan/rtl_433_tests/tree/master/tests

[Isa001]

Files from https://github.com/merbanan/rtl_433_tests/tree/master/tests can be decoded. That's ok.

According to several spectrum captures from rtl_433, signals on 433.92 are very very weak. It's obvious that the decoding is impossible in these conditions.
RTL_433 considers it too weak, but I can tell you these signals are not too weak.

Out of curiosity, I recorded on others frequencies with strong known signals.
On the spectrum capture, these signals are still very weak. Even with the fixed maximum gain (-g 49.6)
I noticed 2 strong carriers. Maybe it can have a side effect.

However, I'm sure some signals are very strong on these frequencies.
I can prove it with sdrsharp and his spectrum.

Others scripts like aisdeco2, adsb and others works very well.

When rtl_433 got the datastream from sdrsharp, decoding is working very well with a maximum signal strength. (sdrsharp + rtl433 plugin)

Maybe there be a problem with AGC enable/disable ??