Hi Henry, > Why is it only schottky mixers that have the problem - won't any high > level passive mixer have the same problem? Yes, I would think so, but I have not tried any other passive mixer than the standard schottky mixers that are so populer for home- brewing these days. Surely unbalanced mixers sould be much worse...
I would also think the problem is the same for MOS switching mixers of various kinds. Maybe the AM sideband noise can be removed by the conversion of the LO from sinewave to squarewave but I am not so sure that would help because AM modulation would probably cause a varying mark to space ratio instead. By carefully designing the stage that converts from sine to square one should be able to avoid it, (make a test by putting 5% AM modulation on the LO and see whether the tone comes out of the mixer when there is no RF signal.) Any mixer including switching mixers is an FM detector to some degree. Apply FM modulation at e.g. 1 kHz modulation frequency to the LO without any signal to the RF port. Increase the frequency swing until there is noticeable 1 kHz audio in the mixer output. 73 Leif / SM5BSZ
