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RFI on AO40 2.4 GHZ Downlink



Unable to complete some QSOs due to the presence of noise 
on the 2.4 GHZ downlink. It's so loud, that it's hard to
peak the antenna on it because the sidelines show nearly 
as much noise as as the main lobe. Also the noise peaks at
many different freqs. It sounds like 200 or 300 HZ sawtooth
modulation. It is on from about 1 to 5 seconds and off about
1/2 to 4 seconds. It can vary quite a bit. The on and
off times are just typical.  Maybe a 50 to 70 percent average
duty cycle. I haven't listened enough to tell if it is worse
at certain times of the day. The sig strength is from about 15db
over S9 to 20 over! The noise floor shows S6. I can't hear
the satellite noise floor at any time.

*Can this be Microwave oven noise?*

The Down East Microwave 
preamp seems to have some problems. (maybe related?) It 
yields a much better S/N ratio at 7 Volts (near the drop-
out voltage of the regulator.) There is also a a popping sound 
every 300 MS  all across the band at all times. It's too fast
to observe the sig strength with the FT736 S meter, but seems 
to kick up to S7 or S8.

I should have tested the preamp as soon as it was delivered instead
of months later!  

Any ideas?

Ken,  K5MBV

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