W.r.t the current discussions on ubitx transmitter woes ... the route forward that I chose was to order LPFs plus the relay board from QRP Labs. My thoughts were to use a 2nd Arduino Nano clone configured as an I2C slave to allow the Raduino to communicate with the LPF board over I2C. This would require some very minor code changes to send band change info to the new filter board.
This solution would give me clean CW TX from 160m through 10m but does nothing to address the spur problem on the higher bands when using SSB nor the more recent concerns about other IMD.
This got me thinking that for another $20 I could just order the QRP Labs 5W PA kit and build a separate 160m to 10m CW TX with raised cosine wave shaping.
I do mostly CW anyway so giving up SSB wouldn't be a big loss for me.
So now I am considering the option of just using my ubitx as an HF receiver. The RX works quite well so if I just forget the TX, at a little over $100 for my v3 ubitx is was still a great deal IMHO.
Has anyone else thought of just designing a separate TX board for use with the V3/V4 ubitx? I know that this sounds like giving up ... but in many ways this could be a simpler solution than attempting major surgery on the existing ubitx.
I have yet to package my ubitx in a permanent enclosure so for now I am going to put it aside and wait a month or two to see if there is a better option.