Small noise at the beginning of a .sub file transmission

Sub-GHz
#1

I noticed while transmitting to a Acurite-986 temperature monitor with a .sub file that there is always a small signal that isn’t in the data right at the beginning. I can move it by inserting something like 10 -1000000 at the beginning of the .sub file. I can then see a tiny signal from the 10 and a second later my desired transmission. Has anyone noticed undesired noise that’s not part of the data at the beginning of a transmission? I’m using rtl_433 with RTL-SDR and Audacity to look at what’s transmitted.

In either case (noise or generated silence at the beginning) my device isn’t responding to the message but my RTL-SDR setup does. I can receive correct transmissions from quite a distance. It must be more forgiving than the actual device.

#2

when playing a raw file, everything that the flipper heard at the time of recording is reproduced, including the noise of the air. rtl_433 is written so that it carries everything that it hears above the rssi threshold set for it to a useful signal, and this is its problem. the flipper analyzes the entire data stream, regardless of the signal strength, choosing only the useful one. cut the raw file from the noise of the air, leave only useful data, then rtl_433 will normally receive them

#3

I think I understand. In my case I’m building the .sub file from scratch (based on a recorded sample of the real thing and cleaning it up) so there should be no noise. If I have something like:

Filetype: Flipper SubGhz RAW File
Version: 1
Frequency: 433920000
Preset: FuriHalSubGhzPresetOok650Async
Protocol: RAW
RAW_Data: 216 -276 216 -276 1600 -1560 1600 -1560 1600 -1560 1600 -1560 220 -520 220 -880 220 -520 220 -880 220 -520 220 -880 220 -520 220 -520 220 -520 220 -880 220 -520 220 -880 220 -880 220 -520 220 -880 220 -880 220 -880 220 -880 220 -880 220 -880 220 -880 220 -880 220 -520 220 -520 220 -880 220 -520 220 -520 220 -520 220 -520 220 -520 220 -520 220 -520 220 -520 220 -520 220 -520 220 -520 220 -880 220 -880 220 -520 220 -880 216 -276 216 -276 1600 -1560 1600 -1560 1600 -1560 1600 -1560 220 -520 220 -880 220 -520 220 -880 220 -520 220 -880 220 -520 220 -520 220 -520 220 -880 220 -520 220 -880 220 -880 220 -520 220 -880 220 -880 220 -880 220 -880 220 -880 220 -880 220 -880 220 -880 220 -520 220 -520 220 -880 220 -520 220 -520 220 -520 220 -520 220 -520 220 -520 220 -520 220 -520 220 -520 220 -520 220 -520 220 -880 220 -880 220 -520 220 -880 216 -276 216 -276 1600 -1560 1600 -1560 1600 -1560 1600 -1560 220 -520 220 -880 220 -520 220 -880 220 -520 220 -880 220 -520 220 -520 220 -520 220 -880 220 -520 220 -880 220 -880 220 -520 220 -880 220 -880 220 -880 220 -880 220 -880 220 -880 220 -880 220 -880 220 -520 220 -520 220 -880 220 -520 220 -520 220 -520 220 -520 220 -520 220 -520 220 -520 220 -520 220 -520 220 -520 220 -520 220 -880 220 -880 220 -520 220 -880 216 -276 216 -276

Receiving this with rtl_433 shows me:

;pulse data
;version 1
;timescale 1us
;created 2022-12-29 10:30:57-0500
;received 2022-12-29 10:31:02-0500
;ook 141 pulses
;freq1 433929760
;centerfreq 433920000 Hz
;samplerate 250000 Hz
;sampledepth 8 bits
;range 42.1 dB
;rssi -0.1 dB
;snr 27.0 dB
;noise -27.1 dB
1088 1004
216 280
212 280
1600 1564
1596 1564
1604 1560
1596 1568
212 508
252 876
212 508
248 876
216 504
248 844
248 508
248 504
220 516
244 836
248 512
248 840
244 876
248 480
244 868
252 840
248 868
220 872
248 872
216 872
244 876
216 868
248 476
...

note that “1088 1004” at the start. I’m not sure where that comes from. Maybe it’s an artifact of receiving with rtl_433. I’ll try to receive another way. Thanks.

#4

So I don’t think it’s rtl_433 because I see it received with CubicSDR. Here’s part of the capture with the strange signal at the beginning highlighted.

audcap
audcap1593×1499 141 KB

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#5

Have you tried recording the signal using the Flipper? I believe they(Acurite) send out a signal once per minute IIRC.

#6

Yes, I originally recorded it with the flipper but it had recorded a bit of silence before so I didn’t get the noise. If I trim the silence I get that little noise at the front.

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