Howard WB2VXW has posted a PDF (download here) of circuit diagrams that would be incorporated on a single add-on PCB as an addition to the uBitx board.
Please respond to Howard if you see anything to improve or other features to add in. You may also want to respond if you are interested in a PCB or a kit has Howard may offer it as a PCB or kit with sufficient interest.
U4 is an audio amp to replace the problematic TDA2822. U3A and Q1 etc. form the AGC circuit, not original. U3B is a log amp the drives an analog S meter (the digital one is better) that is in my enclosure. U1 is a switch to put the CW filter in or out of the circuit. (Note there is a drawing error +VM shouldn’t connect to U3.)
The Cheybchev 750 Hz LPF 0.1 db ripple
I/O JP2 and JP3 plug into connectors soldered on the underside of the uBitx. The odd pins connect to the Raduino and audio connectors. The even pins are hardwired to the uBitx.
Chebychev Low pass filters, 0.5 dB ripple for the external linear amp I posted previously.
Relays for the above filters. Copied from and driven by the uBitx
New driver for IRF510s. connects between VR1 and the output of T10 which is removed.