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Hearing AO-40 MB at 150 deg. squint? <ANSWERED!>

Thanks to Dom I8CVS, an obvious RF smart-guy, there is a textbook answer to
my question. I have included Dom's message to me for reference. At first, I
thought "diffraction" as a misspelling. <grin> NOT SO! Check Page 21.3 of
the 2001 ARRL Handbook, and you will read an excellent piece on "knife edge
diffraction", a fairly well understood RF anomaly.

It seems what was happening was that a side lobe of the helix antenna was
striking the edge of AO-40, between the bottom and side, and caused a
"shadow zone" of RF to wrap around the spacecraft.

Also, thanks again to the ham on this mailing list that spotted the fact
that Borders Book Stores was selling 2001 ARRL Handbooks for about $10 or
so. What an outstanding reference, and an incredible price. (It had to be a

Steve Diggs, W4EPI

(Here's hoping DOM will send me a reply QSL card for our AO-40 contact; I
even sent him an IRC...hi..hi..)

-----Original Message-----
From: i8cvs [mailto:domenico.i8cvs@tin.it]
Sent: Friday, June 15, 2001 5:55 PM
To: w4epi@mediaone.net; AMSAT-BB
Subject: R: [amsat-bb] Hearing AO-40 MB at 150 deg. squint?

Hi  Steve,

Probably  a  strong side lobe of the AO40  helix is diffracted against the
corner edge of the satellite metallic structural radiating back to the

Propagation of MW by diffraction on the crest of mountain i.e. Monte
Bianco,is currently used  for QSO between Italy and Switzerland.

Tank you for your very interesting remark

73 de i8CVS Domenico

----- Original Message -----
From: Steve Diggs <w4epi@mediaone.net>
To: <amsat-bb@AMSAT.Org>
Sent: Friday, June 15, 2001 3:01 PM
Subject: [amsat-bb] Hearing AO-40 MB at 150 deg. squint?

> OK, guys I have a question here:
> I am sitting here listening to a very weak AO-40 MB, with Nova indicating
> squint is over 150 degrees. Distance is 6,100 miles, and elevation is 33
> degrees.
> How can this be? The antenna is pointed away from me, and I have a big
> of satellite between the antenna and me. Is the signal bouncing off
> something and then coming back to me? I don't understand how the signal is
> propagating in such a manner that I can hear it in this configuration.

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