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Cheap Satellite Tracking

I'm working on a $20 printer port interface to the Radio Shack $64 Antenna
Rotator to simplify tracking and monitoring the digital and FM birds.
While not suitable for a high-gain OSCAR class station, this will let
anyone with a dual-band FM rig operate via at least a dozen of the amateur
digital and FM voice satellites at low cost.  

Taking advantage of the geometry of low earth orbiting satellites, you can
cover 96% of all access times with over 10 dB gain using only a fixed
10 deg elevation and a short 4 to 6 element UHF beam.  Here is why:
 * 4-6 elements is enough gain to be above digital threshold 
 * 4-6 elements is enough to be above FM threshold for voice
 * Most LEO birds are mostly vertical most of the time.
 * LEO satellites are below 45 degrees for 95% of the time
 * The other 5% of the time, they are 6 to 10 dB closer in range

Here is a plot of overall gain for the elevation angles shown.  Notice
the cumulative percent column showing 96% of all pass times are below 50
degrees yet still give you at least 10 dB gain on the bird.

--- --- ----- ----- -------- -------- ------------
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

* Data for an 800 km orbit.  For the ISS at 370 km, the times below 30
degrees are even 6% higher than shown.

Note:  If your horizon is blocked below say 5 degrees anyway, then
elevate the beam to 20 deg to improve gain (+2 dB) for everything else.

The interface is built on a small perf board and placed inside the rotator
housing with a small wire coming over to your  PC printer port.  APRStk
will have the software drivers.  The software uses the fixed RPM timing to
keep track of the beam and it will auto-re-sync periodically.  ALso, the
original control/indicator can still be used for manual pointing.

Other typical 24 volt AC rotators without indicator circuits can be used.

de WB4APR@amsat.org, Bob

See my APRS LIVE pages    http://web.usna.navy.mil/~bruninga/aprs.html
See APRS SATELLITES       http://web.usna.navy.mil/~bruninga/astars.html
See MIM/Mic-E/Mic-Lite    http://www.toad.net/~wclement/mim2.htm

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