dumphfdl working with ka9q-radio

[ka9q]

Thought people might like to know that I'm successfully feeding dumphfdl from my ka9q-radio multichannel receiver, listening to all 106 listed channels simultaneously. In fact, I have it running on the ham SDRs at KFS on the same antenna that ARINC uses to receive HFDL (and ATC) transmissions to the San Francisco station. It's not polished yet, but it's working.

At the moment I'm feeding a separate copy of dumphfdl for every channel with an IQ receive stream with 16 bit samples at 12 kHz. I also successfully fed a single copy of dumphfdl with a 200 kHz wide ka9q-radio channel centered in the 8 MHz aviation band, with the center frequency and the individual 8 MHz HFDL channels all specified to dumphfdl. I haven't looked closely enough yet to see which configuration is more efficient.

To save some CPU in single channel operation I tried dropping the input sample rate to 8 kHz, with the receiver centered on the HFDL modem carrier 1.44 kHz above the nominal USB suppressed carrier frequency, but this didn't work. Since dumphfdl accepts an IQ stream, it should have worked. Is there a minimum usable sample rate greater than that implied by the modulation bandwidth?

[ka9q]

I've since converted to one wide ka9q-radio channel feeding one instance of dumphfdl for each band. I'm not sure there's a huge performance difference, it works both ways. The only gotcha is that you have to be somewhat careful in picking sample rates (and bandwidths) for each of the wideband channels, as ka9q-radio requires those sample rates to be multiples of 200 Hz, and some values result in inefficient FFT blocksizes.

I've pushed my configuration files to my project at ka9q/ka9q-radio.