Upon completion of my QDX transceiver I was happy to see it was capable of full output on 60m and had no apparent attenuation of signals on receive.
According to Hans G0UPL, the QDX uses the 40m LP filter when operating on 60 meters. Also, even harmonics are largely suppressed thanks to the characteristics inherent in the push-pull design of the QDX's PA.
I decided to have a look at the QDX output on 60 meters and am happy with the results:
|2nd harmonic -49dB|
|3rd harmonic -58dB|
Other QDX-related postings are here.