I’ve decided to spend a bit of time trying to see if I can add native support for the AirSpy SDRs to dump1090-fa. I have the plumbing done and I can actually decode samples although not well enough for real use. Right now I have 2 stumbling blocks that I could use some help with.
First some background…
The AirSpy R2 can:
- Sample at 2.5, 10, 12, 20 and 24 Msamples/sec.
- Output Float32-IQ, Float32-Real, Int16-IQ, Int16-Real, UInt16 real and “raw” formats.
- It can only use the 20 and 24 samples rates with the non-IQ output formats however.
- Expects a fixed sample rate of 2.4 Msamples/sec.
- Expects Int16-IQ or Int8-IQ data formats. (We’ll leave the Q11 variant out of the mix for now)
The first problem is that even if the AirSpy uses an IQ supported sample rate, dump1090’s 2.4 sample rate isn’t supported at all. It’s also kinda pointless to use the AirSpy for such a low sample rate. By setting the AirSpy’s sample rate to 12 and the format to Int16-IQ, I was able to feed the converter and demodulator with every fifth sample (12 / 2.4 = 5) but the results are disappointing to say the least. So demodulators that can operate at the higher rates would be needed.
The other problem is that, if we want to use the 20 and 24 rates, we can’t use the IQ format. That means converters for at least the Int16-real format.
My math/signal processing skills aren’t up to the task but I’m trying to get some help.
In the meantime, any thoughts, suggestions or offers of help would be appreciated.
You can see what I’ve already done here…