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Re: Cheap Satellite Tracking



I will certainly be interested!

Are you aware of the IR remote system for this rotor? I've been 
thinking of hacking it for computer control.

Jim Sullivan N7TCF

On 23 Jan 2001, at 13:55, Bob Bruninga wrote:

 > 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.
 > 
 > EL  PCT CUM-% RANGE RNG-GAIN ANT-GAIN OVERALL-GAIN
 > --- --- ----- ----- -------- -------- ------------
 > 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
 > 
 > 
 > ----
 > Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
 > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
 > 


Jim Sullivan

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