Broken hardware or mistake on my side?

[Tobster77]

I try to receive a Honeywell doorbell type DW915s ringing. The doorbell uses 868Mhz and a protocoll called ActivLink. I think found it in this list .

I bought a simple SDR USB stick (https://www.berrybase.de/dvb-t/dab/fm/sdr-usb-stick-mit-rtl2832u-chipsatz?number=125187) and tried first in Home Assistant, but I could get no readings. I also tried a 315M remote, but no readings as well.

I then installed the stick on a Windows PC together with Zadig drivers. Here I could enable verbose mode: Looks like both the doorbell and the remote cause some receivable data, but it seems not to be proper. For example, the doorbell causes some data on honeywell_cm921_decode, but this does not seem to be a clear reading, only debug data.

Logs are attached for 315M, 868M and - to be sure it is no frequency issue - 868.35M.

Am I too silly to configure this, or is this a hardware issue?

Thanks for your help!
rtl_433_868M.txt
rtl_433_315M.txt
rtl_433_868_35M.txt

[ProfBoc75]

@Tobster77

Unfortunately your usb stick is not using a good tuner. Fitipower FC0012 is not known for being sensitive, quite the contrary, and especially at 868Mhz it's close to its limit.

Interference must be limited, use a good usb cable extension 50 cm / 1m , to reduce computer noise, a good antenna. Then play with -g gain level and -Y options could help.

[Tobster77]

@ProfBoc75 Thanks for your advice!

I now used the following command line on the Windows PC:
rtl_433 -f 868M -g 0 -F kv -v -Y autolevel

Then the magic happened:

New defaults active, use "-Y classic -s 250k" if you need the old defaults

[Protocols] Registered 230 out of 266 device decoding protocols [ 1-4 8 10-12 15-17 19-23 25-26 29-36 38-47 49-60 63 67-71 73-85 87-100 102-105 108-116 119-122 124-128 130-149 151-161 163-168 170-175 177-197 199 201-215 217-232 234-241 243-244 246-247 249-259 261-266
[Input] The internals of input handling changed, read about and report problems on PR #1978
[SDR] Found 1 device(s)
[SDR] trying device 0: Realtek, RTL2838UHIDIR, SN: 00000001
Found Fitipower FC0012 tuner
[SDR] Using device 0: Realtek, RTL2838UHIDIR, SN: 00000001, "Generic RTL2832U OEM"
Exact sample rate is: 1000000.026491 Hz
[SDR] Sample rate set to 1000000 S/s.
[Input] Bit detection level set to 0.0 (Auto).
[SDR] Tuner gain set to Auto.
[Input] Reading samples in async mode...
[SDR] Tuned to 868.000MHz.
[Auto Level] Estimated noise level is -17.2 dB, adjusting minimum detection level to -14.2 dB
[Baseband] low pass filter for 1000000 Hz at cutoff 200000 Hz, 5.0 us
[Auto Level] Estimated noise level is -19.1 dB, adjusting minimum detection level to -16.1 dB
[Auto Level] Estimated noise level is -20.7 dB, adjusting minimum detection level to -17.7 dB
[Auto Level] Estimated noise level is -22.1 dB, adjusting minimum detection level to -19.1 dB
[Auto Level] Estimated noise level is -23.4 dB, adjusting minimum detection level to -20.4 dB
[Auto Level] Estimated noise level is -24.4 dB, adjusting minimum detection level to -21.4 dB
[Auto Level] Estimated noise level is -26.2 dB, adjusting minimum detection level to -23.2 dB
[Auto Level] Estimated noise level is -27.6 dB, adjusting minimum detection level to -24.6 dB
[Auto Level] Estimated noise level is -28.6 dB, adjusting minimum detection level to -25.6 dB
[Auto Level] Estimated noise level is -29.8 dB, adjusting minimum detection level to -26.8 dB
[Auto Level] Estimated noise level is -30.9 dB, adjusting minimum detection level to -27.9 dB
[Auto Level] Estimated noise level is -31.9 dB, adjusting minimum detection level to -28.9 dB
[Auto Level] Estimated noise level is -30.8 dB, adjusting minimum detection level to -27.8 dB
[Auto Level] Estimated noise level is -31.8 dB, adjusting minimum detection level to -28.8 dB
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
time      : 2024-11-09 15:28:30
model     : Honeywell-ActivLink                    Class     : Doorbell      Id        : 74f14
Battery   : 1            Alert     : Normal        Secret Knock: 1           Relay     : 1             Integrity : PARITY
[Auto Level] Estimated noise level is -24.4 dB, adjusting minimum detection level to -21.4 dB
[Auto Level] Estimated noise level is -26.2 dB, adjusting minimum detection level to -23.2 dB
[Auto Level] Estimated noise level is -27.5 dB, adjusting minimum detection level to -24.5 dB
[Auto Level] Estimated noise level is -28.6 dB, adjusting minimum detection level to -25.6 dB
[Auto Level] Estimated noise level is -29.7 dB, adjusting minimum detection level to -26.7 dB
[Auto Level] Estimated noise level is -30.8 dB, adjusting minimum detection level to -27.8 dB
[Auto Level] Estimated noise level is -31.9 dB, adjusting minimum detection level to -28.9 dB
[Auto Level] Estimated noise level is -30.8 dB, adjusting minimum detection level to -27.8 dB
[Auto Level] Estimated noise level is -31.8 dB, adjusting minimum detection level to -28.8 dB
Signal caught, exiting!

I tried to translate these settings to the following conf file and moved back to my Home Assistant computer, which is even closer to the doorbell.

frequency 868M
output kv
gain 0
verbose 5
pulse_detect autolevel

Here, I get fewer Auto Level adjustments, but not the doorbell. Note, the noise level is not around -30dB but -15dB which is worse, right?

tarting rtl_433 -c /config/rtl_433.conf
rtl_433 version 24.10-3-g4fa37568 branch master at 202411051225 inputs file rtl_tcp RTL-SDR SoapySDR
New defaults active, use "-Y classic -s 250k" if you need the old defaults
[Protocols] Registered 230 out of 266 device decoding protocols [ 1-4 8 10-12 15-17 19-23 25-26 29-36 38-47 49-60 63 67-71 73-85 87-100 102-105 108-116 119-122 124-128 130-149 151-161 163-168 170-175 177-197 199 201-215 217-232 234-241 243-244 246-247 249-259 261-266
[Input] The internals of input handling changed, read about and report problems on PR #1978
[SDR] Found 1 device(s)
[SDR] trying device 0: Realtek, RTL2838UHIDIR, SN: 00000001
Found Fitipower FC0012 tuner
[SDR] Using device 0: Realtek, RTL2838UHIDIR, SN: 00000001, "Generic RTL2832U OEM"
Exact sample rate is: 1000000.026491 Hz
[SDR] Sample rate set to 1000000 S/s.
[Input] Bit detection level set to 0.0 (Auto).
[SDR] Tuner gain set to Auto.
[Input] Reading samples in async mode...
[SDR] Tuned to 868.000MHz.
[Baseband] low pass filter for 1000000 Hz at cutoff 200000 Hz, 5.0 us
bitbuffer_add_bit: Warning: row count limit (50 rows) reached
bitbuffer_add_bit: Warning: row count limit (50 rows) reached
bitbuffer_add_bit: Warning: row count limit (50 rows) reached
bitbuffer_add_bit: Warning: row count limit (50 rows) reached
bitbuffer_add_bit: Warning: row count limit (50 rows) reached
[Auto Level] Estimated noise level is -16.4 dB, adjusting minimum detection level to -13.4 dB
[Auto Level] Estimated noise level is -15.4 dB, adjusting minimum detection level to -12.4 dB
bitbuffer_add_bit: Warning: row count limit (50 rows) reached
bitbuffer_add_bit: Warning: row count limit (50 rows) reached
bitbuffer_add_bit: Warning: row count limit (50 rows) reached
bitbuffer_add_bit: Warning: row count limit (50 rows) reached
bitbuffer_add_bit: Warning: row count limit (50 rows) reached
bitbuffer_add_bit: Warning: row count limit (50 rows) reached

What am I doing wrong?

[ProfBoc75]

@Tobster77

Noise at -15 dB could be ok, depends on the signal noise ratio (snr) should be around 10 / 12 dB.

Try to get the figures with option -M level -M noise:1 , 1 will give you a noise information every second

If you have a RSSI close to 0 dB , then SNR = 15 dB with Noise = -15 dB it's ok, very good signal.
But if you have a RSSI = -10 dB, then SNR = 5 dB with Noise = -15 dB, not ok, not enough, could work but less success.

Again, lot of attention around the antenna and nothing around the stick and antenna that could generate rf noise like a computer, a screen, any electronic device generates rf interference/noise.

Another option is -Y filter=150 will filter all signals with pulse width less than 150 us, your device is little more so should help (try filter=100, filter=50 ... ), you have other -Y options like -Y magest (for FSK signal) or -Y ampest (for OOK signal) , -Y minmax (for FSK), those options could help too, you have to try one by one and find the good one for you, lot of possibilities here.

Edit: if the usb stick box is made of plastic, so it doesn't filter out any external interference, you can wrap a small sheet of aluminum foil around it (2 or 3 wraps around it are sufficient) to create a Faraday cage / electromagnetic shield, which will also reduce noise too.

[Tobster77]

OK, this looks good. Conf file is:

frequency 868300000
output kv
gain 0
verbose 5
pulse_detect magest
report_meta noise
report_meta level
report_meta noise:1
pulse_detect filter=150

Output is:

[Auto Level] Current noise level -15.0 dB, estimated noise -15.0 dB
[Auto Level] Current signal level -0.9 dB, estimated noise -14.6 dB
[Auto Level] Current signal level 1.8 dB, estimated noise -11.3 dB
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
time      : 2024-11-10T14:14:28.013466+0100
model     : Honeywell-ActivLink                    Class     : Doorbell      Id        : 745bc
Battery   : 1            Alert     : Normal        Secret Knock: 1           Relay     : 1             Integrity : PARITY
Modulation: FSK          Freq1     : 868.2 MHz     Freq2     : 868.3 MHz
RSSI      : -0.7 dB      SNR       : 14.5 dB       Noise     : -15.2 dB
[Auto Level] Current noise level -15.1 dB, estimated noise -12.3 dB
[Auto Level] Current noise level -15.1 dB, estimated noise -13.7 dB
[Auto Level] Current noise level -15.0 dB, estimated noise -14.5 dB

If I got your point right, that is a quite usable signal, right?

[ProfBoc75]

@Tobster77 yes, looks good for me.

You can remove -M options if you want, up to you (it's verbose only)

Notice that, because of the filter=150 this could exclude some sensors, since it's working as a low pass filter, any other sensor with lower pulse than 150 us will be filtered out.

If you want to change your usb stick dongle, you may look at Rafael Micro R828D tuner (formerly R820T) or better Rafael Micro R860 (formerly R820T2).

R820Tx does not exist anymore since years even if Chinese low-cost web sites propose usb RTL SDR dongle supposedly based on this component, most of the time it's not the good tuner and supplied with FC0012/13 tuner which does not cover the full range of frequency up to 1.7 GHz, and not only, the sensitivity and noise are not good too.

Fitipower FC0012 tuner frequency range is from 22 to 948.6 MHz, bad sensitivity, bad noise floor.
R828D/R860 tuner frequency range is from 24 to 1766 MHz, much better, with improved filtering, better sensitivity.

[Tobster77]

Thanks a lot! The cheap stick now works well. Your proposal of the filter setting was the game changer... :-)