Re: FW: [amsat-bb] Lock on Tracking

[Bruce Bostwick <lihan161051@xxxxxxxxxxxxx>]

Muxing four feeds to one RX would be essentially the same as coning, 
but without motorized feed steering a la missile guidance radar. 
Same thing as the Doppler DF arrays used by the LoJack system (and 
some ham DF setups!) .. basically a matter of determining 
phase/amplitude of the error signal and getting an error vector which 
you then use to steer the dish by feedback.  Would make for a complex 
system but could track most GTO/inclined GEO sats pretty well.

Using four separate RX's, you could use them for a "diversity 
reception" scheme to demod while you're tracking, and use a simple 
comparator feedback scheme to steer the dish.  This might be more 
transparent in terms of operation, but it would require splitting at 
least the LNA/downconverter part of the feed system, and would 
require some sort of simple and sensitive tap/AM detector at each IF 
to feed control voltages to the steering unit and the diversity 
switch.  Doable, but it would take me a few months to hack together 
unless I had a limitless supply of junk to pull from .. LOL

>-----Original Message-----
>From: Rod Smallwood
>Sent: 11 December 2002 14:59
>To: 'Dave Johnson'; ',amsat-bb@amsat.org'
>Subject: RE: [amsat-bb] Lock on Tracking
>
>
>Sounds good but I don't think AO40 would look for me
>I think I would have to look for it!
>
>Having thought a bit more about it you could do it in
>hardware if you had four antennas and four receivers (or one
>muxed around the four antennas). Another possibility
>would be to have four feeds at different angles to
>the dish. And finally there's the flat phased array
>which is steered electronically. (anybody know how?)
>
>Rod G8DGR
>
>
>
>-----Original Message-----
>From: Dave Johnson [mailto:Dave.Johnson@ddat.co.uk]
>Sent: 11 December 2002 13:31
>To: Rod Smallwood;
>Subject: Re: [amsat-bb] Lock on Tracking
>
>
>Hi Rod,
>
>An active solution might be to do the the equivalent of what deep space
>satellites do when they lose lock on the earth for some reason, they
>'cone'.
>In other words they set up a motion which subtends a cone of the
>radiation
>pattern of the antenna. At some point in the motion around the cone the
>signal strength will increase and that will give an indicaton of the
>direction. The satellite then manoeuvres 'the cone' in than direction,
>and
>reduces it's diameter and continues to do this repeatedly until a lock
>is
>found. A cone of zero angle.
>
>A neat trick but I'm not sure that my 5500 would cope with all than
>movement!
>
>- Dave G4DPZ


-- 
<BGB>
                  --... ...--  -.. .  -. ..... ...- -...
              Bruce Bostwick  N5VB  Austin, TX  Grid EM10DH
     ARRL / Austin ARC / Travis Co. ARES / ARRL + W5YI Vol. Examiner
                    mailto:lihan161051@earthlink.net

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