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RE: Re: "Precision" Antenna Pointing



Oh, heck, I figured I'd jump into this discussion....

This all sounds so complex....Yes, Steve and I determined *some* alignment
benefit from tracking the Moon, stars, planets and other things with Nova.

I'm playing with a digital solution for the Elevation component.  That
solution being an Accelerometer.  Yup, you can buy them in chip form and
they give you a voltage reading for acceleration or in our case gravity.

If you turn the digital accelerometers on their side, they read gravity and
if you turn them at angles to that gravity, they will read angles!!!

So, you hang an ADC on one, read it with a micro and... poof you have an
"digital inclinometer".

Ok, so what to do with Az.  Well, that's a little more complicated, but
there still might be a digital solution.  They make digital solid state
"fluxgate" compasses.  Again, an ADC to a micro and you are done.  There is
one problem with any compass, it's influenced by conductive materials or in
most cases, large hunks of metal, you know towers, tripods, etc.

Ok, so how do you do this with long runs (the compass and inclinometer are
up a tower or on the roof, etc)?  I'd propose you use rs485 and bring the
signals down to a PC or some such.

In thinking about this, these digital devices *may* only move the point of
calibration away from the beams and to the device itself.  Just means you'd
have to set the "device" to N and 0 and then adjust the beams to be in
parallel with both axis's of the "device".  Probably not that hard.... But I
haven't tried it yet.

Oh, well, back to code do just that....We'll see.

BTW, I saw the link to the eme unit, but I couldn't tell, that looked like a
gyro (btw, you could do it with one of those too) or something... way too
many wires coming out of it.  Me, I want no moving parts, and single board
integration.

But then it begs the question.  "Do we really need +-1 degree accuracy?"...
My vote... Nope.  Now with that said, I don't plan on pointing a 10ghz horn
or a laser at ao-40.  You'd need better than +-1 for that... probably more
like +-.1

Just my .02
Alan

-----Original Message-----
From: owner-AMSAT-BB@AMSAT.Org [mailto:owner-AMSAT-BB@AMSAT.Org]On
Behalf Of howard@hanlincrest.co.uk
Sent: Monday, December 31, 1979 9:01 PM
To: Louis A. Mamakos
Cc: Clifford Buttschardt; Dave Guimont; jeff w griffin;
amsat-bb@AMSAT.Org
Subject: RE: Re: [amsat-bb] "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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