[amsat-dc] Re: Fwd: inquiry about homebrew az-el systems

Tom Clark tom.k3io at gmail.com
Sun Feb 24 19:45:31 PST 2013


I responded to Samudra Haque after a couple of preliminary Emails with 
this idea on lo-cost az/el rotors. I presented the idea at an AMSAT-DC 
meeting 3? years ago and showed a working kludge example. Somewhere in 
my archives I have the Powerpoint from then and I will dig it up if 
there is any interest, particularly from someone who wants to do some 
development!


The rotor scheme I described in my presentations is based on the DISEQC 
consumer antenna control protocol 
(seehttp://en.wikipedia.org/wiki/DiSEqC 
<http://en.wikipedia.org/wiki/DiSEqC>) pushed by EUTELSAT and found in 
nearly every backyard satellite dish system (see 
http://www.eutelsat.com/satellites/pdf/Diseqc/associated%20docs/position_app_note_v1.pdf). 
The DISEQC scheme superimposes DC (to run the rotors, switches, 
downconverters, etc) plus RF (typically 500-1500 MHz IF satellite 
downlinks) plus control (PWM 22 kHz tones) and it has an amazingly rich 
instruction set. Many BUD (Big Ugly Dish) receivers include DISEQC 
controllers for controlling antenna position, polarization, 
bandswitching, etc.

Most of the DISEQC rotors cover only 180 degrees and are very suitable 
for elevation with 1 degree precision (see 
http://www.sadoun.com/Sat/Products/PowerTech/Sadoun-DG380B_HH_Motor.htm) 
for example. Sadoun is a main suplier in USA.

However I have found one 540 degree DISEQC Azimuth rotor 
(http://www.solidsignal.com/pview.asp?p=rotr100&d=eagle-aspen-rotr100-one-cable-antenna-rotator-(rotr100) 
<http://www.solidsignal.com/pview.asp?p=rotr100&d=eagle-aspen-rotr100-one-cable-antenna-rotator-%28rotr100%29> 
).

Total cost for a pair of az/el rotors is < $200 but the antennas that 
could be controlled must be pretty small. My application was for a solar 
radio telescope using a couple of small DirectTV Ku-band dishes.

I'd LOVE to find someone who was interested in developing a 
microcontroller/interface  for DISEQC az/el use. The coding should be 
pretty simple. Also someone needs to figure out a scheme to adapt the 
"crooked pipe" on the elevation rotor to couple to a real antenna. Let 
me know if you can find someone who is interested.

Also, if anyone is interested, you might want to browse the Sadoun & 
Solid Signal web sites where you will also find DISEQC controlled 75 ohm 
RF switches good for low power use well into the microwave spectrum.

73, de Tom K3IO (ex W3IWI)


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