Of the 3 boards (all v4) that I have had contact with, and the reporting of power to frequency on multiple BITX20 threads, the dip in power on 40 meters is fairly consistent. No one has jet explained why, and as Jerry stated, it is further away from the LPF than the 30 meter band using the same LPF.
On the one board that I have tested for harmonics, 40 meters is the worst. I believe that some of that is because the 3rd is below the 30mhz LPF that is in on all bands. However why then is 80 meters not as bad?
There is something going on with the 40 meter CW transmit side that does not add up with the data that I have seen so far.
Anyone any ideas?