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Re: Satellite Rotators (fixed elevation)

Quoting Roger Kolakowski <rogerkola@aol.com>:

> I apologize...I think I squashed this inquiry by taking it off track:
> Paul...KB3NDS asked:
> >Since I can't move the assembly on the vertical axis, I have to get
> the
> nominal elevation for most passes and lock it in there<
> Hi Paul..
> You will get many opinions from 10 to 30 fixed elevation depending on
> the
> sharpness of you beam lobes. A very high percentage (I've seen 96%
> quoted)
> of your passes will be below 50. Also, as the satellites approach
> their
> peak elevation relative to your location, they are closer to you so
> don't
> need as much signal to hit them.  In these cases the edges of your beam
> lobe(s) will usually suffice.
> However, when your pass is just starting or has a lower max elevation,
> you
> need more rf concentrated toward the horizon because the satellite is
> further away. This sort of moves you away from splitting the 50 50/50
> and
> just picking the 25 mark.
> Bob Bruninga has put a lot of effort into simplifying satellite tracking
> and
> suggests a fixed 10 with a 4 to 6 element beam for LEOs. I have seen
> higher
> degree angles touted by others.
> A last consideration might be ...whart is your real horizon?  If you
> have
> mountains (hills) or thick stands of trees (buildings) that obstruct
> your
> horizon up to 20 that should probably become your zero horizon and
> your
> tilt should be up from there.
> If you want to drive yourself crazy, Google : fixed elevation beam
> satellite
> It's getting warmer here in the once frozen North...put it up and move
> it
> around until you are happy!
> Enjoy!
> Roger

Roger's advice summarizes the consensus quite well, and following it will
give you quite a bit of fun. It's worth knowing, however, that the
elevation and azimuth patterns of horizontal and vertical yagis differ. By
consulting L. B. Cebik's interesting article on the topic,[1] I determined
that I wanted to tilt my horizontally yagi (on 2m) down further than the
vertically polarized one. This has improved the performance of my station
on mode B when under 10 deg. (I am on a hill with a very clear horizon.)

I'm thinking that having both yagis mounted half way between vertical and
horizontal orientation (but still 90 rotated from each other) would best
make their patterns equivalent.

Does anyone know of any NEC-based experimental results that show the
patterns of vertical and horizontal yagis tilted up as we do in fixed
elevation work?


73, Bruce
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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