i did some more testing of the ubitx with the homebrew specan (as opposed to the rigol), i have some good news, bad news and good news.
1. good news : the homebrew specan does a better job than the rigol.
2. bad news : the specan revealed that the even order transmit harmonics will go down below -40dbc only if we carefullly balance the bias current between the IRF510s. it is very touchy. i can't see how anyone can get it right without a spectrum analyzer
4. good news : i have replaced the two filter harmonic filters ?with four filters. that also means, two more relays. it is more complicated, i know. but at least, it works.?
for those who want fewer bands (choose between 3.5 mhz and 7 mhz for the lower filter and 14 mhz and 28 mhz for the upper band), or they are alright to use external tx filters, the current design will do. for those who want all in one, wait a few days for me to update the ubitx page.
