RF22: Can see transmission, but not read it

Hi all,

I hope you are all staying healthy :slight_smile:

I have a commercial weather station that I am trying to interface. There is a sensor part, which sends the data through a RFM22B. On the other side, there is a USB stick, also containing a RFM22B (+ a 328p and a FTDI serial converter).

I would like to read the transmissions between the devices. Well, for fun and the curious kid in me :). I know the frequency is 434.0MHz. I hooked a RFM22B to a Mini 3.3V/8MHz and watched the frequency and - got nothing.

I already did a couple projects with RFM22Bs, so I have some experience. The particular sketch I am running (sorry, I am traveling and donโ€™t have it with me. Will post asap) does receive data from other devices at the same time. It uses the RadioHead RF22 library and just waits for any transmission, in promiscuous mode (hence would not discard messages not addressed to itself).

I did some spectrum scans and can confirm that the center of the frequency is 434.0. Also, while monitoring the RSSI on 434.0, I can โ€œseeโ€ the transmissions happening.

Unfortunately, I am not able to read them. The RF22 does not fill .recv() and does not trigger .available().

Do you have any idea what I could try to read/receive those transmissions? Every hint is appreciated :slight_smile:

Thanks!

You probably need to know the data rate of the transmitted signal.

Thanks for the idea!

I did cycle through all the available modem configurations with no success. I was of the opinion that if it was off, I would still receive "something", but just garbage. Definitely something I can revisit once I am back home.

GoingForGold:
Thanks for the idea!

I did cycle through all the available modem configurations with no success. I was of the opinion that if it was off, I would still receive "something", but just garbage. Definitely something I can revisit once I am back home.

I would not assume that the library you are using would cover all possible permutations that the RFM22 can be configured with, more likley just has a very very limited set of standard configurations.

I recall that the data rate setting register is 16 bit, which would give 65536 possible settings ?

I would also not assume, but its a long time since I have played with the RFM22, that if the data rate is out you will always see 'something'. If the preamble detect fails (because the data rate is wrong) that would cause syncword detect (if used) to fail and thus you might see nothing.

GoingForGold:
I already did a couple projects with RFM22Bs

I did some projects with the RFM22B, back in 2011-2013, using a PICAXE no less.

Although the RFM22B (Si4423) are cheapish; the same size RFM98, which is a LoRa device, is a good deal easier to work with and capable of around 10-30 times the distance.