[amsat-bb] Relay controlled antennas

[Dave Guimont <dguimon1@xxxxxxxxxx>]

A great deal of interest prompted questions with regard to eliminating 
rotors for
satellite work.  A relay switching system developed 6 years ago envisioning 
their
use on AO40 was tested on the low orbit birds, and it works very 
well.  Initially
the switching was done manually.

Chris, vk6kch, wrote a neat little program that attaches to IT that 
controls the
switching by selecting desired switching ELs from 10° to 50°.  I built a little
control box so I can easily change that elevation while experimenting with 
various
antennas.

Any combination can be selected, but a homebrew quadrifilar and a homebrew 
collinear
J-pole on 435 works very well....The J-pole gives ~4 db gain to about 30° 
EL.  Switching
to  the quadrifilar gives ~4 db from that EL to 30° "on the other side".
~4db hemispheric gain with no rotors "ain't too shabby".

An article on the antennas appeared in the AMAST JOURNAL, sep/oct 1996.

Pick your combination of gain (beamwidth), and switch to get whatever 
hemispheric gain
you wish.  Geodesic 435 12 db patch arrays??  Perhaps dreaming, the relay 
system would cost more
than a rotor system.  Your goal may be somewhere inbetween...

The 2 M J-pole uplink was powered by an old Kenwood TR 751 modified with an 
outboard
pot to enable complete control of a 100 watt linear from 3 watts to full 
output.

AO40 xmit on 435 will require some new thinking, but possibly doable...

Relays good to 1.2 gigs can be had very inexpensively at Hamtronics, and 
probably others.

Chris is in the process of revitalizing the program, and some of us can 
hardly wait.

With the advent of AO7 I might just be tempted to put my arrays back up, 
hardly worth
the effort for the FM voice 2 user bird coming up, however.

The following at:

http://home.san.rr.com/doguimont/uploads

quadfil1.zip and collinj1.zip apply...

Glad to answer any questions for the interested...


            73, Dave wb6llo@amsat.org
                    Disagree: I learn....

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