All, The 50 MHz oscillator can be divided by two, yielding a 25 MHz source that can be zero-beat calibrated in the uBITX if WWV is not receivable. A counter works best for me. Once calibrated I can listen to AM broadcast for long periods of time, right on advertised frequency. Changing sidebands sounds the same.
Jim, regarding the BFO: I use a white noise source modulating the transmitter while viewing the spectrum on a cheap SDR receiver or Spectrum Analyzer (I like the SDR best). You then adjust the BFO frequency for best band pass and sideband reduction. You can do it on the receive side with a stable signal generator but it takes longer. The visual spectrum is nicer, you can see the carrier, etc. Then you can check by switching sidebands to compare different frequencies and their comparative levels on receive. I built a 2-tone oscillator with noise generator into a candy tin with an audio amp and speaker. Holding the microphone over the speaker makes for a rapid test. Jacks are available for more accurate and cleaner testing but I find that I seldom use them since the speaker and such are quite adequate. -Don
Don, ND6T