Narrow AF Filter
This 50 Hz wide audio frequency filter really helped me to make CW DX's. The filter is toggled on/off with the Speech button on the front panel of the IC-751A.
The home-made filter is embedded
into a free space in the transceiver:
Detail of the filter. Three
band-pass filters on 6 ferrite pot cores:
Schematic of the filter:
Schematic of the logic switching
the filter on and off:
And the PCB layout of the filter:
