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Re: AO-40 beacon question



The best analysis I've seen of the S2 pattern was done by Colin Hurst,
VK5HI.  You can read his write up at
http://www.amsat.org/amsat/sats/ao40/articles/AO40Squint.html

There is a very deep null in the S2 antenna pattern at a squint angle of 45
degrees.  Depending on the gain and noise figure of your receiving system
you might not be able to hear the beacon through that null.  There is also a
fairly strong sidelobe around 60 degrees which, combined with the low range
at that point in the orbit, makes for some very strong signals.

Also keep in mind that the satellite's attitude is being moved which can
make squint calculations questionable.  The ALON/ALAT of 10/0 on 17 Feb also
noted that they would need to start moving the attitude again in 7-10 days.
Looking at the telemetry archive I see that on 25 Feb, orbit 1067, the
ALON/ALAT was 8.9/2.8.  I suspect we'll be getting an update from the
command team soon when they've reached another holding attitude.

Lee-KU4OS

----- Original Message -----
From: "Jon Ogden" <na9d-2@speakeasy.net>
To: <amsat-bb@AMSAT.Org>
Sent: Sunday, March 02, 2003 8:31 AM
Subject: [amsat-bb] AO-40 beacon question


[snip]
> But then I had the following question:
>
> Is it possible at certain heights and certain squints to be out of the
beam
> of the S2 antenna?  Even though I can "see" the bird, is it possible that
> the elevation is too close to earth and so the antenna pattern is two
> narrow?  That coupled with the squint could make it such that some people
> could hear the beacon when others can't.
>
> I haven't looked at the specs of the S2 antenna.  I know this sort of
thing
> would have been an issue with the S1 antenna with its higher gain and
narrow
> pattern.  But could it happen now?  Was just trying to make some sense out
> of why I couldn't hear it.
>
> A half hour later or so and I heard the beacon fine.
>
> 73,
>
> Jon
> NA9D
>
> -------------------------------------
> Jon Ogden
> NA9D (ex: KE9NA)
>
> Citizen of the People's Democratic Republik of Illinois
>
> Life Member: ARRL, NRA
> Member:  AMSAT, DXCC
>
> http://www.qsl.net/na9d   <- Updated on 1/22/03!!!
>
> "A life lived in fear is a life half lived."
>
>
> ----
> Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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