Re: [amsat-bb] Lock on Tracking

["Edward R. Cole" <al7eb@xxxxxxxxxxxxx>]

My two cents:

First of all, predictive auto-tracking is probably easier to accomplish.

However, my 2.4m dish (which is slated to be outfitted for mode-LS and
3cm-eme*) was originally a ship-board VSAT terminal (on ku-band) and
utilized signal-strength to lock the antenna position and polarization.  It
was used for tracking geo-stationary satellites but then the ship moved in
three-dimensions on the sea, so high antenna slew-rates were required.

I sold the microwave electronics at surplus so no longer have it.  I
believe it basically generated an agc signal that was coupled to the gyros
in a feedback circuit.  Since three spacial-variables were controlled some
method of logic was used, but used only a single dish feed (the feed did
have two orthogonal linear polarizations).

You could possibly use your radio's agc and input it using an A/D to a
parallel port where a program would smooth the numbers and alternately
generate azimuth and elevation commands...but sounds complicated to me!   I
know that microwave eme stations utilize Moon-noise to keep their antennas
peaked on the Moon.  I don't know if that is a manual method or automated.

When I worked for NASA, they calibrated the big dishes using a conical or
"inward spiral" movement of the antennas around a signal source until the
receivers indicated they were at peak signal.  But this was not used as a
operational pointing methodology, only for precise calibration of antenna
pointing.  As I remember they utilized precisely known strong quasar
sources for this.  Beamwidth of the 64m dish was on the order of 20-minutes
of arc. at 2295 MHz.

Ed - AL7EB
*2.4m dish:  
I plan to use a dual-band patch feed (attached on the side of the 10G feed)
for my DEM 144/1268 15w-conv and 2401/435 Drake (probably with a DEM preamp).
3cm-eme will utilize the existing wr-90 waveguide and "Chapparal feed", to
a 4-port w/g switch, db6nt w/g preamp, DEM 10368/144 xvtr, and a 50w Varian
TWT.


At 11:24 AM 12/11/02 -0500, Howie DeFelice wrote:
>Commercially, sites using inclined orbit GEO's and INMARSAT maritime
>installations use a step track method. The antenna is moved in small
>increments in a pattern. Several signal strength readings are averaged at
>each position and the antenna is nudged toward the center of the position
>that yields the best average signal strength. This method would work fine
>for AO-10, AO-40 or any other relatively slow moving satellite.
>
>Howie AB2S
>
>----- Original Message -----
>From: "Al Lawler" <al.lawler@oracle.com>
>To: "Ben" <b-fisher@uiuc.edu>
>Cc: "Rod Smallwood" <Rod@sbs293.customer.demon.com>; "AMSAT-BB"
><amsat-bb@AMSAT.Org>
>Sent: Wednesday, December 11, 2002 10:17 AM
>Subject: Re: [amsat-bb] Lock on Tracking
>
>
>>
>>     You could concievably average the
>> peaks, then try to drive the antennas based
>> on the averaged signal, combined with a bit
>> of AI knowledge of what sort of correction
>> last worked,  but it would probably take
>> a relatively custom  solution for
>> each installation, I'd  imagine
>>
>> (and things like blowing leaves,
>> or varying precipitation intensity
>> would make it exciting to debug... :^)
>>
>>   -al
>>
>>
>>
>> Ben wrote:
>> >
>> > Hi Rod
>> >   I have thought about building a system that would work by using the
>signal
>> > strength from the satellite as reference than a simple error amplifier
>> > circuit to drive the AZ-El. But this may be very difficult if the signal
>> > from the satellite fluxuates allot. With fast enough circuits and
>motors, it
>> > seems possible, but it would probably take a good computer programmer to
>> > develop a workable algorithm.
>> > My thoughts
>> > Ben K9BF
>> > ----- Original Message -----
>> > From: "Rod Smallwood" <Rod@sbs293.customer.demon.com>
>> > To: <amsat-bb@AMSAT.Org>
>> > Sent: Wednesday, December 11, 2002 4:16 AM
>> > Subject: [amsat-bb] Lock on Tracking
>> >
>> > > Unless I am much mistaken everybody uses predictive tracking.
>> > > Has anybody had any experience with Radar style tracking
>> > > where the system locks on to the target (ie AO40) and follows
>> > > it?
>> > >
>> > > Rod (G8DGR)
>> > >
>> > >
>> > >
>> > > ----
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>> > >
>> >
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