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Re: UO-22 azimuth-only system


I really appreciate all of the input I've received as a result of my question
on azimuth-only tracking of LEOs.  It's helped me to hatch an idea...

It's seems to all come down to a trade off of beamwidth vs. gain.  If your
70cm antenna had a 13.42 dBi gain and an 84-deg. beamwidth, you could mount
it on a cheap rotor or even use an armstrong system.  Aim it at an elevation 
of 35-deg. and your gain at the horizon would still be 11.42 dBi.  Straight up,
the antenna would have a gain of 8.42 dBi.  With that kind of gain/beamwidth,
you could start out each pass ahead of AOS azimuth and then move it only once
or twice per pass.

The antenna I'm thinking of is a flat-plane reflector, described by L.B. Cebik,
W4RNL, at http://www.cebik.com/f432.html.  This antenna could be built with a
1-inch PVC tubing support frame and mesh-screen reflector.  The reflector would 
be roughly 2-ft. square to cut down on wind loading.

Install a crossed-dipole feed system, adjusted to achieve 100-ohm impedence, and you
could have a simple RG-62 (93-ohm) phasing system for RHCP/LHCP.

With that kind of gain.  I could even use the antenna (with a switched preamp,
of course) for AO-40 uplink.  It would give me more gain than I get from the
11-element beam I'm using now!

This would be a perfect match for my existing AO-40 downlink antenna, which is 
a 76-element loop yagi with a beamwidth of 10.7 degrees and 23.5 dBi gain 
(Directive Systems 1276LY). Actual usable beamwidth seems to be about 15 deg.  
Because the workable elevation of AO-40 here in Kodiak varies from only 6-to-20 
deg., I'm able to leave the elevation fixed at 13 deg. and work all elevations.  

The loop yagi has a wind loading of only 1.1-square feet and weighs just 5-lb. 
So, I could conceivably mount both antennas on an inexpensive TV rotor!!!  
Wouldn't need tracking software at all.

Something must be wrong with this idea.  It sounds too good to be true...

Any comments?

John Pfeifer - KL0WN
Kodiak, Alaska

At 09:50 AM 8/31/2002 -0400, Bob Bruninga wrote:
>On Fri, 30 Aug 2002, Jonathan Naylor wrote:
>> what I did was to put an azimuth only system together with a vertically
>> polarised 9ele yagi for the uplink with a fixed elevation of 30
>> degrees. This meant that the 3dB points of the yagi occured at the
>> horizon and at 60 degrees of elevation.
>Here is my table from my http://www.ew.usna.edu/~bruninga/rotator1.html
>--- --- ----- ----- -------- -------- ------------
>10   32   32  3030     0       10         10
>20   35   67  2440     2       10         12
>30   17   84  1827     5        8         13
>40    8   92  1460     6        6         12
>50    4   96  1190     8        2         10
>60    2   98  1020    10        0         10
>Two important points.  Below 10 deg where 30% of all passes are, the
>satellties are also 10 dB further away.  You dont want to give up ANY gain
>on the horizon.  So point your beam at 10 degrees which gives full gain
>from 0 to about 20 or more where you need it most.
>As the satellite gets higher, it is closer and so any drop in gain above
>40 deg is more than made up for by the satellite being 6 dB closer and
>only being there 8% of all in-view times.
>But if your terrain will not let you see down to the horizon (you have to
>live on a hill), then instead of 10 degrees from the horizon, just mount
>the beam 10 degrees above what you CAN see and you will have an optimum
>Hook it to a radio shack or any cheap rotator and there are almost 18
>satelites you can pickup easily...  If you happen to have a THD7 or D700
>then run APRStk (dos) and it will autotune the radio, auto configure the
>internal TNC's, and auto rotate the radio shack rotator for a fully
>automated satelite monitoring station for all the digital and FM
>And I am not "pushing APRStk" here.  I wish OTHER amateur satellite
>tracking programs would provide the simple two-bit LPT1 port (right, left)
>control for such simple ($20) rotator systems.  See the web page above...
>We dont need full AZ/EL OSCAR class arrays and $800 rotator controller
>systems for *ANY* LEO satellite.  And all of our satelltes are LEO's
>except for OSCAR 10 and 40.  I wish more authors and AMSAT programmers
>would recognize this and support the simple LEFT-RIGHT cheap-TV rotator
>interface...  I think it would bring in more people to working the LEO
>de WB4APR
>Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
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John Pfeifer - KLØWN - Kodiak, AK - www.johnpfeifer.com

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