05 Mar 08 17:25, TOM WALKER wrote to ROY WITT:


 RW>> TW>IF you rembember some of your Amsat Theroy you should

 TW> rembember you need to do Special Tracking to follow the Frequency
 TW> change becasue of the Doppler effect as the Sat Travels form
 TW> Horizon to Horizon.

 RW>> It's not a frequency change, it's a polarization change...That's why
 RW>> you'll see different looking antennas which are capable of switching
 RW>> from one polarization to the other. Circularly polarzed antennas
 RW>> work best for amateur sat work.

 TW> Sorry Roy but besides the Polarization chnages, That are easily
 TW> adjusted for by using either a "Cross Polarized" or "Circular
 TW> Polarized" Antenna.

That's what I said.

 TW> You also have the Dopper Effect "Frequency" Changes which
is an Even
 TW> bigger problem in Ham Sat communications.

Actually,  that's a phase shift, not a frequency change. That can be
helped by using the phase shifting antenna, such as those I mentioned
above.

 TW> And I would point to the
 TW> computerized control Interfaces that are o nthe Market! As one
 TW> manfacturer(Spectrum Internal Inc of Concord MA) puts it his Device
 TW> "Automaticly "TUNES" your Radio, IN Real Time, to
track the Doppler
 TW> Changes".



 TW> There are also devices to automate the THIRD prolbem in Sat Tracking.
 TW> IT's constant movement across the Sky requires not only Azmith
 TW> Changes but also Elevation changes as the Sat moves for Horizion to
 TW> Horizion.

Yes, that is easily done with two antenna rotors, one for elevation and
the other to follow the sat across the sky. It's even easier if you have
an automated system that will do the tracking for you.

                R\%/itt



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