[Hackrf-dev] Looking for a HackRF-CW-RX.grc

[Kevin Reid]

On Oct 4, 2015, at 11:02, Hajo Dezelski <dl1sdz at gmail.com> wrote:

> I have been a ham for over 25 years and am doing only QRP with CW. So
> I thought to use the HackRf as a second receiver for the CW-portions
> of the amateur bands.
> 
> Although the HackRF is more dedicated to the exploration of the
> spectrum above 30 Mhz, I know that later I have to use a up-converter
> to cover the range from 0 - 15 MHz, but that's secondary in the
> moment.

You don't necessarily need an upconverter to receive at HF at all -- the signals will just be weaker, and you might get more interference due to lack of filtering.

> Has someone developed a HackRF grc file for a core CW-RX for e.g.
> 14.000 to 14.100 Khz which could be understood by a ham who
> understands the traditional way of signal processing.

I just made one for you.

It's not optimized for tuning in a narrow band because I wanted to keep it minimal. What you'd want to add is basically an intermediate decimation/filtering stage to select the 20-meter CW band -- by putting this before the spectrum display you “zoom in” so it's more feasible to see signals, and it also may make the final bandpass filter less expensive (cascading lower-decimation filters rather than trying to go all the way to audio sample rates in one step).

It does USB only. For LSB, make the bandpass filter frequencies negative (-200, -3000); for CW, make the filter narrower and adjust the tuning arithmetic so that the number in the GUI is the midpoint of the passband (the “BFO” frequency, even though there's no BFO) rather than the 0 Hz AF point.

Remember that the HackRF has a DC offset, so you want to set the "hard_vfo" value somewhere away from the spectrum you care about, then use the "soft_vfo" (like your IF frequency in a superhet receiver) to compensate for that frequency offset. The "Final RX Freq" number is what you're actually listening to.

Theory: The SSB demod essentially occurs in the “Frequency Xlating FIR filter” block, which simultaneously does the band-pass filtering, mixes to AF, and changes the sample rate to match the audio sink.

There are many missing features here. The most important one beyond usable tuning controls is being able to set the HackRF's three RX gain settings for best SNR. But you asked for something to get started with yourself.

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-- 
Kevin Reid                                  <http://switchb.org/kpreid/>