Did some measurements on receiving on harmonics of the LO
If all these measurements are correct (not sure) it is terribly clear why you need a good BPF with direct conversion
Erik,
CQX or Receiver module, they are the same.
It is not actually harmonics of the LO although the effect is similar.
It is a Tayloe sampling (switching) mixer, At 3 times signal frequency the theoretical value is about -9.5dB when 1/3 of the samples are taken. And lesser responses at higher odd multiples of RX frequency.
That is the reason a good BPF is required.
Details of the mixer here I do not think this paper actually mentions the higher responses. The 3x response was actually used for early crystal controlled Softrocks, reception using 1/3 sampling rate and no LO is present.
73 Alan G4ZFQ
