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[TowerTalk] Figuring Noon

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Subject: [TowerTalk] Figuring Noon
From: (Rick Mainhart)
Date: Tue, 8 Jul 1997 17:59:51 -0400
Well, that clears things up! :)

A simple way to give you real beam headings regardless of rotor/mast/boom
slippage is to install a fluxgate compass on the boom of each of your
multiple antennas. This way, you can ignore slight skewing caused by not
installing rubber sheeting as Steve recommended. 

The indicator(s) can be used as-is, or you can use the sine-cosine data
into a dedicated microcontroller to give you a three or four decimal
place azimuth display. Note that while you may have a three or four
decimal place display, your accuracy is limited to the A/D resolution,
and the math solution you use (and, of course, the accuracy of your
original installation).

If that isn't enough, you can install a rotary encoder with 4000
steps/revolution (commonly available, if not a bit pricey) in your rotor.
This, when properly counted (use the Z output to let you know when you
pass south for calibration), should give you .09 degree resolution. 

If accuracy is what you want, you CAN use differential GPS to tell you
where the end of the boom is on it's circular path. Differential GPS
(DGPS) has an ACCURACY of approximately 1 meter, but it's repeatability
is much finer. Accuracy, in this case, means you know, with absolute
precision, your location on the planet. Repeatability simply means you
aren't all that concerned EXACTLY where you are, but rather you are
precisely where you were a little bit ago. Repeatability is the more
desired measure here.

Probably the best (leaving the term "best" undefined for the moment) way
to achieve accuracy, repeatability, immunity to slipping, and (best of
all) the high bucks approach is to mount a CCD camera on the end of your
antenna boom, looking down. Directly under the path of this camera (as
the antenna turns) is an illuminated scale marked in degrees, minutes and
seconds. For the economy model, you provide a monitor (color of course)
to display the azimuth readout. The deluxe model has the video passed
along to a high speed graphics processor that determines the heading,
adds some random digits beyond the decimal point and displays this
heading on a color monitor approximately the same size as the economy
model. The display font will need to be identical to that used on the
outside scale, to allow rapid transition from the economy to the deluxe
model without retraining.

The use of a CCD camera allows using an IR light source to keep the
neighbors from reporting UFOs, and to keep helicoptors from trying to
land (your two element 40M beam DOES cast an "H" shaped shadow,

So, there you have it. Accuracy beyond usefulness, sound engineering (if
somewhat misapplied), and something to brag about on the reflector!

I guess I'll start working on the 6-1/2 digit VSWR meter, should come in
under $5000.00 or so.


Rick, WB3EXR


This message has been sent with a computer and monitor pointing directly
at true north ... for best results, turn your monitor to true north
before reading.


On Mon, 7 Jul 1997 23:10:23 -0500 (Roderick M.
Fitz-Randolph) writes:
>I would like to put in my $.02 worth regards the efforts of those that
>attempt to get their antennas oriented correctly on true north.
>Many of the amateur fraternity (and I am included in this group) are

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