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S band diagnostics (was Re: AMSAT-BB Digest, Vol 1,Issue 112)



Quoting Michael Tondee <mat_62@netcommander.com>:

> I have tried all week to be able to hear the S-band downlink with a BBQ
> 
> grill dish and AIDC 3731 converter. I checked aim of my antennas and can
> 
> receive a signal when a signal source is hanging off the dish but no joy
> 
> as far as hearing the bird itself. I don't have an antenna for L band 
> yet so I can't transmit.
>  I'm very discouraged and about ready to yank the dish/downconverter off
> 
> the mast and give up.
> 73,
> Michael, W4HIJ

I would yank them off the mast, but not give up. Others have suggested that
the beam width of the setup you describe is quite narrow and might be
requiring better pointing than you have right now. Here's a procedure to
see what's what.

I have one of the self-modified CalAmp $6 units It works much better
hand-held than on the mast, and I have just a 8 dBi gain patch antenna on
it. On future S-band opportunities, I would try pointing the d/c by hand
with its feed alone, no dish, and see if that works. If you can hear
something, then I'd say there's a pointing issue. (For the sake of
comparison, I can hear part of a 20-30 deg. max el. pass through a window.
Not good copy, but enough to prove things are tickety-boo while the snow is
flying.)

If you can't hear anything at all by this means, I wonder if your d/c is
sensitive enough. It worries me that your rf source has to be 'hanging off
the dish'.  I have an rf source like the one described in the latest Amsat
Journal, but with no antenna to speak of. I can still hear it as a weak
signal indoors through a window about 15' from the antenna when the rotor
is vaguely pointing my way. When I first was working on the d/c and hadn't
peaked the filter, the source had to be no more than an inch or two from
the d/c. At this point, the d/c wouldn't receive Echo.

Steve, WI2W, gave me some excellent advice, which I think should be shared
with others. Noting that our CalAmp $6 d/c's were a bit marginal, he
recommended that instead of building a more narrow beamwidth antenna, I
should get a mast-installed preamp for 2.4 gig. The plan is to keep my
broad-beam antenna (which is better for the LEO situation) and improve my
gain and noise floor with the preamp. SSB USA has them for $125ish. His is
the sensible plan if one's goal is a easy-to-use LEO s band setup. I'm
interested in building antennas and such, so I'm working on a 15 turn helix
and adding elevation control to my rotor. But by the time P3E and ESEO fly,
I think the preamp will be necessary.

Maybe the next time Echo is transmitting on S band, we'll both have working
systems!

73, Bruce
VE9QRP
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