When I presented the Simple CW Receiver few weeks ago I also mentioned and demonstrated that it is actually a double side band receiver (it’s around 2:35 in the video). This is good for AM and FM, but can be very inconvenient for receiving CW and SSB (single side band). If the station we are trying to receive is surrounded by other stations on the neighbouring channels, these will interfere via the opposite side band. Therefore, it was time to look into single side band reception.
I had some time to improve on the simple CW receiver by adding the frequency translating filter to allow easy tuning within the sampled spectrum. This feature was missing from the previous versions because I did not know how to specify the filter taps parameter of the gr_freq_xlating_fir_filter_xxx block in GRC. Of course, all I had to do was RTFM to find out. GRC is smart enough to allow entering complete python statements (including function calls) for parameter values, so all I had to do was to create a variable filter_taps and use firdes.band_pass(1, samp_rate, low, high, trans, firdes.WIN_HAMMING, 6.76) as value, then use filter_taps as parameter for the xlating filter.