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Re: AO-40 signals



Keith, AMSATs -

I suggest you build a 2400 MHz signal source to use as a reference.  I built
one similar to the one described on this website:

http://www.coloradosatellite.com/SSource/SSource.htm

For the source's antenna, I used a square aluminum plate 2.42 inch (61.5 mm)
on each side, with a hole in the center and a 1.17 inch (29.7 mm) vertical
wire (4 AWG) through the hole.  The oscillator drives the wire, the plate is
grounded.  Built in a plastic box.

It is powered by a 9-volt battery, through a 1N4001 diode to guard against
wrong polarity, a switch, and a 78L05 (NTE 977) 5-volt regulator.  0.05 uF
bypass caps on input & output of the regulator.

This also provides a signal at 440 MHz to plot side-lobes of the uplink
antenna.

I spent several hours today tweaking a 6-turn helix illuminating a 20x22
inch (51cm x 56cm) offset dish.  The signal source is an excellent tool for
this!  I mounted the dish with the feed arm at 0 degrees, put the signal
source 22.5 degrees above the dish, at a distance of 20 ft (6.10m) in front
of the dish.

The dish measured 12 dB more signal, and 18 dB better S/N, than a 17 turn
RHCP helix, assuming the S-meter on my trusty old TS-430S is accurate.

Then mounted the dish to the cross boom.  (It is for "Dish Network 500" TV
in USA.)  It is easy to mount to a cross boom, just remove the 2 bolts for
the skew adjust, rotate the skew 180 degrees, re-install the bolts.  Slide
the mount onto the cross boom.  This puts the dish on its side (horizontal).
Use the dish's "elevation" adjust (now in the azimuth axis) to compensate
for the 22.5 degree azimuth offset.

Photo on www.qrz.com (before mounting to cross boom)

Happy New Year everyone!

Tom Smith KB6A
DM13au, Anaheim, California, USA
cwdxer@concentric.net


----- Original Message ----- 
From: "Keith Bainbridge" <vk6xh@arach.net.au>
To: "amsat" <amsat-bb@AMSAT.Org>
Sent: Tuesday, December 30, 2003 12:01
Subject: [amsat-bb] AO-40 signals


> I've just been listening to the MB on AO-40 , squint 33 degrees and very
> weak signals received here.
> I'm using my 2 mtr dish , 0.65 f/d with a 6 turn helical feed for the
first
> time and I'm surprised how weak the signals are.Before with my patch feed
> that was over illuminating the dish in these circumstances I would have
> expected signals at least S6 as compared to S1 at the present. Is it the
way

<<<snip>>>


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