I put a SotaBeams DSP Audio Filter into my BITX40 and it works great. ?I have a 2nd one that I intend to use for my uBITX.
If you don't want to fuss with installing it in the rig you can get an enclosure for the filter and use it externally on different rigs.
These filters outperform any active audio filter I have ever used.?
There is also a small circuit board that is available from QRP Guys for the W0EB uBITX CW conditioning adaptor.
This helps to make the CW keying more reliable.?
