[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: P3D Orbit Patterns & Fixed Antenna



At 10:00 AM 10/19/1998 -0500, lutzjo@superman.cig.mot.com wrote:
>Greetings,
>
>I'm hoping that some of you satellite veterans can help answer a question
I've
>been considering for quite a while.  I'd very much like to set up an S-band
>receiving capability for P3D, but I really can't afford antenna
>elevation-control equipment.  While I don't profess any particular insight
into
>elliptical orbit mechanics, I do believe it's likely that for any given
point on
>earth, P3D's maximum elevation above the local horizon will follow some
kind of
>pattern.  For example, it might be that for the Chicago area P3D's maximum
>elevation will fall between 20 and 30 degrees every tenth orbit during local
>Spring and Fall (or something like that).  Perhaps the pattern will be
much more
>complicated, but still repeatable.  I don't know.  The point I'm leading
to is
>merely this; if there is a definite pattern, and the repetition rate of that
>pattern is sufficiently high, it's then practical to fix the antenna
elevation
>and control only the azimuth.  Obviously, this kind of approach compromises
>satellite access time, but does simplify station cost and complexity.

It can all be calculated BUT there are many factors involved, many of which
are not completely known like the satellite's final RAAN, ArgPerigee,
inclination, eccentricity, and mean motion, as well as your latitude,
longitude, time of year, etc....ArgP is particularly important.  If it
takes a few years to get us to our final ArgP, your proposed fixed
elevation is going to need continuous adjustment as the ArgP changes.

In reality, I wouldn't worry about not having an elevator rotator for
S-Band.  However, given the high-gain of most S-band antennas, you do need
to be pointing close to the satellite.  Ten degrees off-pointing is going
to me a major dB loss at this freq/gain as opposed to 2-meters.  P3D is
going to "hang" at apogee for a long time (hours).  Why not simply build a
small dish or helix and place it on a camera tripod in your back
yard....point it and then forget it for a few hours.  This would be a lot
better than trying to fix an "average" elevation that will almost never be
very close to what you want.

--  
 __________________________________________________________________________  
  Stacey E. Mills, W4SM    WWW: 	http://www.cstone.net/~w4sm/ham1.html 
   Charlottesville, VA	   PGP key:	http://www.cstone.net/~w4sm/key.asc    	
 __________________________________________________________________________
----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home