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RE: Re: "Precision" Antenna Pointing



I tried to send the following note to amsat-bb yesterday but I
don't think it made it...

Two solutions: place a small non-flammable screen at the
focal point of a dish on the az/el system and calibrate it by
pointing the system at the sun (eg Nova will do this). If the
dish is at least marginally reflective to light, the sun's image
should appear in the middle if you're correctly calibrated.

Even easier if you don't have a dish... on a sunny day make
up one of those homebrew pin hole eclipse viewers out of a
couple of pieces of paper. Align the pin hole device with your
antennas and attempt to automatically track the sun. Whilst
tracking, make manual physical adustments the az/el until
the sun is tracked in the middle of the pin hole 'screen'.

73 Howard G6LVB

--------------Replied message--------------
Date: Tue, 09 Jan 2001 21:57:38 -0500
From: "Louis A. Mamakos" <louie@TransSys.COM>
To: Clifford Buttschardt <cbuttsch@slonet.org>
Subject: Re: [amsat-bb] "Precision" Antenna Pointing

> I confirm your thought about plus/minus two degrees as good
as amateurs
> usually can obtain.  It would be nice if ordinary antenna
hardware would
> do better.  This is barely good enough for S band use even with
a two foot
> dish.  Can we list here how much excess sun noise is gotten on
2400 MHz?
> Be sure and include you antenna system and noise figure if
possible.

My other hole-in-the-head, er, hobby is amateur astronomy.  In
addition
to owning some exquisitly polished chunks of glass, I own a
couple of
german equitorial telescope mounts.  I can routinely aim these
things
to a precision measured in arc-seconds because each of the
axes (RA
and declination since they're equitorial mounts) have an optical
shaft
encoder connected to them.  These provide quadrature outputs
with
4000 pulses per revolution.  These are connected to a small
computer
with some anonymous single-chip micro running on a 9V battery;
after
a calibration process which essentially computes a
transformation
from the X and Y coordinates to (in this case) celestial
coordinates,
it displays the current aiming.

I'd guess that the hardest part of moving this to an antenna
positioning
application would likely be the mechanical aspects of coupling
these
optical shaft encoders to the antenna system.

louie
wa3ymh

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