Re: BITX40 - frequency spectrum - Raduino irradiation - intermodulation products - #bitx40help
Your test equipment is impressive! I would love to have access to something like that.
What you are seeing looks very much like what I reported in a post in March, https://groups.io/g/BITX20/topic/4521126#23229.
It appears to be related to harmonics of the 5MHz LO and 12MHz IF. For a long time I have been working on other projects but I have recently returned to the Bitx40 using Allard's sketch. I believe the answer is to use a 19MHz VFO and switch sidebands by moving the 12MHz oscillator and generating USB to mix with 19MHz and end up with LSB on 40m. To do that I need to change the crystal filter (for a 6 pole??) and get a reasonably steep slope on the lower side.
Fairly major changes.
It would also be interesting to compare the use of square wave and sine wave drive to the final Tx mixer.