Hi Erik -
Thank you!
I have not yet looked at nanoVNA firmware
and supposed more similarity to SDR than evidently exists.
The DSP does quadrature mixing down to DC
so there is no mirror signal to suppress
I need to do homework here:
* do SA612s not feed I and Q into ADC?
* does not mixing always generate sum and difference frequencies..??
sin A cos B = (sin(A + B)+sin(A - B))/2
Oristo