Regarding trying to calibrate with WWV, it actually is easier if you have a second AM receiver when WWV is sending tones. You can then match the tone frequency between the uBitX and the AM receiver much easier than when zero beating as you can do that within a few cycles as opposed to losing the low frequency notes perhaps 100's of cycles before zero beat. Note, to be accurate the 2nd receiver needs to be AM, which eliminates that receiver's error which could be added to the perceived tone frequency if using SSB. That is the technique I used on mine and it is dead on frequency.
=Vic=
Vic WA4THR