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Re: UHF Yagi w/ PVC boom



On Tue, 25 Nov 2003, DC wrote:

> I'm building one of the CLARC 435Mhz AMSAT yagis with 11 elements for
> general AMSAT use.

The term "general AMSAT" use caught my eye.  May I comment:

Higher gain means tighter pointing requirements.

* If you mean AO-40, then it is very easy to figure out what size beam is
needed for your TX output.  I've seen fewer elements do well with 50W
uplinks. AND the tighter pointing requeiments are not an issue, because
for AO-40 you have to have a full AZ/EL array and be able to point
accurately in the first place and it is a slow moving target.

* But if you mean by "general AMSAT" use, all the other satellites which
are all LEO's, then, they have these distinct features:
  - They are 10 to 20 dB closer
  - They move 60 times faster
  - they spend 95% of their in-view times below 45 deg so no elevation
    is required at all.

In this case, a simple 5 or 6 element beam on an AZ rotator tilted up at
about 10 deg will give a broader beamwidth and thus much more forgiving
due to pointing errors... and your antenna system will cost about 10% of
what the AZ/EL systems do.  And you are not as dependent on exact KEPS.
And even when the satellite does go exactly overhead, remember that it is
10 dB closer than it was when it was on the horizon, so you still
hear it..

Just a point.
Back under my rock..
Bob


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