Lief, What you say accords with my understanding of the numbers however I did not fully appreciate their significance.
Why is it only schottky mixers that have the problem - won't any high level passive mixer have the same problem? Henry. Leif Asbrink wrote: > Hi Henry, > > >> Could you explain why in a little more detail? >> >> (I thought that AM noise was not a problem in balanced mixers?) >> > > When you feed an LO signal into a schottky mixer the power level is > high. A low level mixer would need +7 dBm or so. The noise floor > is at perahps -164 dBm/Hz (NF=10dB) The mixer is balanced so it > would suppress AM modulation by perhaps 30 or 40 dB so AM noise > would have to be -130 to -140 dBc/Hz to not create problems. That > is easy at a frequency separation of 10 kHz, but at a separation > of 100 Hz it is not so easy. Supply voltages have to be filtered > through RC filters with big electrolytic capacitors of good > quality to avoid producing AM modulation. > > http://www.sm5bsz.com/linuxdsp/hware/optiq.htm > > Also phase noise will cause problems. A schottky mixer is also > an FM detector although the sensitivity for FM modulation is > a bit lower than the sensitivity for AM modulation. Close range > phase noise is often much higher than AM noise...... > > 73 > > Leif / SM5BSZ > > > > > > > > ------------------------------------ > > Yahoo! Groups Links > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
