Dim-witted me took dozens of tries, but I *finally* found Evan's post on how he dealt with the 20 meter third-harmonic:
/g/BITX20/message/100269
Good news: After much grinding, I now have -50DBc for the third harmonic of 14 meters.?
I go to thinking that one of the main differences between the 7300 and the sBITX is the case.? I did some quick ohm readings and found that none of the case screws had low resistance to the heatsink.? I ground down the powder coating on all corner connectors, the corresponding sides, and around the screws that mount the heatsink to the case.? I just fired it up, and though not as clean as the 7300, it is still legal.
I would suggest that the v2 have the case fully grounded.? It would be easier to clear the case corners before assembly.? Also, the corner connectors should not be powder coated.? They should be bare aluminum.
73
Evan
AC9TU
So when I return to the project, I'll work on making even better connections.? ?I noted that the points where case meets threaded blocks are not painted, but maybe I'll have to do more than that?? ?At the same time, I'll probably upgrade the MOSFET insulators to aluminum nitride.? ?;That should only impact the thermal conduction, not the spurious responses.? ?If Evan got his 14m 3rd harmonic to -50, perhaps I can get the 20 meter 3rd to be legal.? ?This really seems like filters are being hamstrung somehow.? ? It is such a great little radio, gotta solve these issues of production.
73,
Gordon KX4Z
