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Automatic AMSAT Antenna Rotators



On Fri, 9 May 2003, Frederick M. Spinner wrote:

> You know, the funny thing here is that the computer programs all ASSUME
> that you are using a Yaesu G5500 rotor.

It is crazy that more software doesnt support the ubiquitous 24 VAC garden
variety TV rotators.  I know this is apples and oranges, (AO-40 precision
pointing versus the other 20 LEO amateur satellites), but it is SO easy to
control a standard TV rotator...

My APRStk does, and so with an old DOS laptop, my rotator points to every
satellite that comes above the horizon, and tracks it and I hear every
bird automatically  (not AO-40).  (It also auto-tunes the Kenwood D7 and
D700 and selects the right baud rate (1200 or 9600 or voice) and tunes
Doppler.

THe only interface is two bits on the parallel LPT1 port on the PC.  One
bit says go RIGHT, the other says go LEFT.  There is no need for a shaft
encoder because these rotators rotate at a near constant speed which the
program learns.  Prior-to or at the end of any pass that is near the SOUTH
limit, the software turns the antenna into the SOUTH limit to
re-calibrate if needed.

Mine has run for years and is always within 10 degrees or so which is all
you ever need on LEO birds.

I'm not pushing my software, I just wish more modern satellite tracking
programs did this same simple thing.  Its not accurate to one degree, but
it is absolutely good enough for LEO's.  Oh, and of course, you dont need
elevation for LEO's either, since 70% of the time they are all below 30
degrees and only 5% of the time are they above 45 degrees.  And when they
are, they are 10 dB closer anyway so you don't need to be  pointing at
them and can still hear them.

AND it lets you use any old JUNK rotator or even if you have to buy one,
it costs only about $60...  not $600 like the Yeasu's (plus the $250
driver card)...

The PC interface is just an optoisolator and a Triac.  Cost less than $20.

   See http://www.ew.usna.edu/~bruninga/rotator1.html

What could be easier... Let me summarize the algorithm:

* BIt 1 on the PC's LPT1 port means go right
* Bit 2 on the PC's LPT1 port means go left.
* COnnect to your 24 AC TV rotator thru the optoisolators/Triacs
* Software always knows where the antenna is by keeping track of how
  far it has moved the antenna.  One RPM means 6 degrees per second.
* Re-alignment is trivial and can be done at any time:
  1) Press RE-SYNC key if you want to force a re-sync.  PC just
     drives antenna east for one minute.  Bingo, Antenna is pointing
     south!  (Rotator hard limit is aligned to south).
  2) Automatically at the END of any pass that leaves the antenna within
     45 degrees of south, the PC waits to be sure three are no other
     satellites in view and then it drives the antenna towards SOUTH for
     10% longer than it calculates it will take to get there.  This also
     then forces a realignment.
* Thus there is never any long term drift.  My antenna is always within
  about 10 degrees of being right on as months and years go by.  And that
  is all you need for LEO's.  (Dont use a 22 element LONG yagi, that is
  overkill for LEO's.  Use a short 10 dB gain antenna tilted up at about
  10 degrees and you wont miss anything..

And you dont have but $50 invested in the rotator system. And if you run
APRStk on an old throw-away DOS laptop, you wont have to worry about
lightening taking out your Pentium... either...

de WB4APR, Bob


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