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I'm currently having a bit of trouble with a project I'm working on, I'm trying to synthesize a radio signal from my doorbell to see if I can reply it without needing a file (thought it would be a good way to start learning about synthesizing signals in general). I have a flow graph in gnuradio that is able to generate a similar pattern to my doorbell signal, and when I open the original signal and my created signal in audacity they seem similar:

similar signals

Yet when I play the generated signal, the doorbell doesn't ring. Upon further inspection, I notice that the waveform used by the doorbell isn't similar to mine:

different waveforms

Whereas my waveform is a cosine wave, the doorbell's waveform is oscillating within itself.

My main question is, how can I generate a signal that my doorbell will recognize? Is there a way that I can possibly create a similar waveform to that of my doorbell's?

I'm fairly new to the subject of generating ASK OOF singals with Software Defined Radio, so I'm sorry if this seems like a simple question.

IndigoRes
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2 Answers2

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That's a really cool project.

First off, the oscillation you observe is probably due to clock offsets and possibly other frequency offsets between your doorbells radio frontend and your SDR radio frontend. In case of the assumed modulation, this SHOULD not make any difference.

Assuming that you know for a fact that ASK OOF is used, make sure that you also insert the pauses between the transmissions. They might be important.

Maybe your doorbell actually implements some kind of security feature and expects a handshake. Try to record the doorbells and the controllers signal. Replay them and check if that works. In case it is a one way transmission, replaying your controllers signal should also let the bell ring.

Check out Balints YT channel. He does a lot of RF hacking and you might find more insight into the topic there too. https://www.youtube.com/user/balint256

blue_screen143
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The cosine wave you generated is most likely the carrier - and it appears hasn't been modulated.

Most of the these devices use ASK/OOK modulation.

See

http://blog.kismetwireless.net/2013/08/hackrf-pt-2-gnuradio-companion-and.html

It uses a HackRF to capture I/Q data of an ASK/OOK signal into a file and the presents a flow chart on how convert the HackRF's I/Q data to complex data GRC can use.

Any device which can capture I/Q data can used - you just need to know the data format of the captured data, e.g., is it signed or unsigned integer, etc.

Cinaed Simson
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