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Re: Lock on Tracking

On Wednesday, Dec 11, 2002, at 12:19 US/Central, Craig Gernaey wrote:

> I can tell you how NASA and others do this at microwave (2 ghz) and 
> higher. They call it auto tracking. They split the feedhorn into four 
> equal quadrants using what is called an orthogonal mode junction.  The 
> signal strength in each quad is continually measured and compared to 
> the others. The dish is automatically adjusted in an attempt to keep 
> all four quads equal. The computer knows which way to adjust the dish 
> based on which quad has the most signal.
> The expense and complexity of this would seem to me to be outside the 
> capabilities of most AO-40 users. It would be of greater advantage for 
> fast moving LEO's than for AO-40 type orbits.

Don't know about that.  If you tap off at each LNA or downconverter and 
use an AM detector, you get a DC voltage you can feed to a box of PID 
(proportional/integral/differential) motor controllers.  Even if the 
sensitivities are different, you'll get the sat somewhere in the 
"boresight" of the feed, and you can use those same DC voltages to 
select which feed goes out the IF.  Most of this could be built into 
the dish mount and remote controlled from your shack.

The big "gotcha" is that they'll have to be PID controllers, and you'll 
have to use gear driven motors with a fairly low top speed to avoid 
overshooting.  Other than that, it's all experimentation and 
engineering, which is within the reach of most folks here ..

"Many that live deserve death. And some that die deserve
life. Can you give it to them? Then do not be too eager to deal out
death in judgement. Even the very wise cannot see all ends." -- Gandalf

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