If you inject a signal of 15mhz near the antenna by radiation (Mid 0 to 30MHZ) and watch the beat up to 0 at the oscilloscope just before the SSB filter (or After the 45mhz filter), you must be well calibrated too.
I did it like that. After that, we have to calibrate the BFO.
Is that a good method for you?
For me, it's work fine