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

No Elevation Rotator Required (was RE: rotator)



I totally agree with Bob WB4APR on this subject.  If he hadn't published 
these numbers a few years ago I probably would have never considered 
working satellites out of an apartment with a "temporary" setup.

This works if your Yagis have 60 degrees of beam width (ie, 5 - 10 
elements.) The 3db beamwidth goes from the horizon to 60 degrees without an 
elevation rotator providing you tilt the antennas up 30 degrees.  From 
experience I've found that because of the decrease in path loss I don't 
start to experience the null until about 75 degrees (though depending on 
which satellite and it's exact location it may be a bit scratchy)

I have a picture of how I mounted them at:
http://www.emilyshouse.com/gallery/AntennaPix/Antennas?full=1

You can see that I simply used a PVC joint to enable me to tilt the 
antennas back while maintaining the centre of gravity.  I've since added 
the 2.4G antenna so I can work mode V/S between the 2m and 70cm antenna - 
you can see a photo of that here:
http://www.emilyshouse.com/gallery/AntennaPix/EEC_Yagis?full=1

So the worse case is if the satellite goes directly overhead.  In that case 
I experience about 30-45 seconds of null depending on the satellite - FO-29 
at apogee can last about 60 seconds, for example, though maybe not even 
that much if you can catch the satellite in one of the sidelobes.  So if 
you put that in context of an entire pass, it's about 45 seconds out of 16 
minutes or in the case of FO-29 it may be 60 seconds out of 22 minutes.

So while not the ideal situation, if you are willing to live with a little 
bit of null when the satellite goes directly overhead and have space/weight 
considerations this is definitely a solution worth considering.

73,

Emily


At 09:08 PM 12/9/2004 -0500, you wrote:
> > but I am using an Alliance on its side for elevation.
>
>At the risk of repeating myself, (for any newcomers),
>remember that you do not need an elevation rotator
>for any LEO satellite, and there are currently no AMSATs
>that are not LEO.
>
>All LEO's are below 20 deg 67% of the time
>All LEO's are below 40 deg 90% of the time but 4 dB closer when above
>All LEO's are below 60 deg 98% of the time but 8 dB closer when above
>
>Thus a small 10dBi gain antenna pointed up about 10 deg will give
>you almost a CONSTANT gain from THe horizon to OVERHEAD.
>And all existing LEO's can be heard easily with that 10 dB.  THus
>no need for elevation at all.  It only adds complexity, frustration
>and more to go wrong.
>
>de WB4APR, Bob
>----
>Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
>Not an AMSAT member? Join now to support the amateur satellite program!
>To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



---------------------------------
W0EEC - CM87tm
AMSAT Area Coordinator - San Francisco Bay Area
http://www.projectoscar.net  http://www.PlanetEmily.com

Join AMSAT!  http://www.amsat.org



---------------------------------
W0EEC - CM87tm
AMSAT Area Coordinator - San Francisco Bay Area
http://www.projectoscar.net    http://www.PlanetEmily.com

Join AMSAT!  http://www.amsat.org
----
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
Not an AMSAT member? Join now to support the amateur satellite program!
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home