Hi Janne, > Guys, what is your experience of the QSD response to a half of the LO > frequency? SDR to masses part 4 mentions about measurements of the > half of the LO frequency leaking through (RXing at 7MHz and injecting > signal at 3.5MHz) only -49dB. > > If this is true, low pass filters don't do enough to keep the output > of the QSD clean. > > I've used BPF on my earlier builds, but not sure this time since the > SDR to the masses part 4 is the only source that mentions about the > half LO frequency problem.
The first order response should be zero. BUT, second order, IM2 could be strong. Check how the response you get for a signal at 3.5 MHz changes with the signal level. Should be second order. 73 Leif / SM5BSZ
