4 ms·
Super cool hack and great write up. It’s nice to see this go all the way from poking at hardware to decompiling binaries and then some signal processing. Kudos.
by ssfrr 6y ago
Super cool hack and great write up. It’s nice to see this go all the way from poking at hardware to decompiling binaries and then some signal processing. Kudos.
You mentioned you were getting distortion/noise when downsampling below 928kHz. Are you lowpass-filtering before you decimate (but after you demodulate)? Otherwise you will get all kinds of aliasing.
Looks like FM radio stations have a bandwidth of 200kHz so you should be able to lowpass with a cutoff of around 50kHz then decimate to 232kHz.
- 0x00000000 6y agoThank you. I am just throwing away samples without filtering because it has to be done as quickly as possible on the device itself in order to send it out before the next chunk of data is ready. It is sort of a hack because I can’t lower the sample rate so it is the only way to make the quantity of data manageable.