Re: R: [amsat-bb] 3m dish applications

["Robert Bruninga" <bruninga@xxxxxxxx>]

Microwave Ovens for EME:

Yes, but...  We dont want to filter the 60 (or 50) Hz, we want 
to use it as *the* modulation for DSP detection?  Maybe I am 
all wrong, but you gave an excellent explaination of why the
magnetron is so wideband, so then, wouldn't the best way to detect
it be to keep the 60 Hz amplitude modulation on it and use that
as the waveform to use DSP to find?

Again, I want to avoid having to "tame" the maggie which is
beyond the scope of most HAMS...  So is the DSP method
possible, or is there so much 60 HZ noise as to mask any
EME signal?  In that case, then maybe the easy approach is
to filter out the 60 Hz (as you say) and then add a superimposed
say 47 Hz waveform?  (or any defined signal easy to detect)...

Bob

>>> <BobsImsai8800@aol.com> 4/5/04 12:03:15 PM >>>
had said:

The 60 HZ noise is easily eliminated in a magnetron with capacitors,
etc., 
and stability can be further increased with voltage regulation.  It is
the 
inherent instability of the magnetron design that gives it a wider
bandwidth. 

Remember the example of the magnetron's operation -- the signal is
generated 
by the electron beam is passing over the top of the magnetron cavities
like 
blowing across the top of a Coke bottle to make it whistle.  A
simplified 
explanation is that the problem with a magnetron is there are many
cavities in it 
and none of them are on the exact same frequency.  With many
oscillators on 
different frequencies, the result is that the band width is very wide. 
The 
cavities also heat and change shape, so that also makes it drift
rapidly.

The only way to tame a magnetron is to source lock it through a
circulator to 
a CW transmitter that has 5 to 10% of the magnetron's power. The
oscillators 
will pull to the frequency.

Bob 
K5GNA
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