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Re: AO-40 70cm antenna side lobes?



Hi Scott,

Interesting...  I haven't updated ALON/ALAT in my tracking program
recently, but it was showing a squint of at least 26 degrees.  28 by
the time I turned of the rig.

So, what happened to my uplink - that's the question.  At the time
I was trying, the satellite was up around 23 degrees to the south-
west.  There's a bit of a hill in that direction, and some trees off to the 
side, but they would have affected S-band much more than U.
And, S was great, so that wasn't it.  The only thing I can think of
is the difference in the squint angle between your QTH and mine as
part of the answer.  The 70cm antenna must have a beamwidth of less
than 26 degrees, and I was on the wrong side of the pattern.

The other curious thing I noticed is that the desensing I usually
get when I key up was almost nonexistant.  Even though my amp was
pumping out all the power it could (pinned the needle on the power
supply!), the rise in the noise floor was very light.  At that power
level it's usually so bad I can't hear myself.  I use the round-trip
delay to hear a little blip of the echo after I unkey.  So, I bet
I've got a cable problem between the shack and the antenna too.

Anyway, I hope we can chat sometime (other than by keyboard...).

73s,

Greg  KO6TH



>From: Scott Townley <nx7u@mindspring.com>
>Reply-To: nx7u@arrl.net
>To: "Greg D." <ko6th_greg@hotmail.com>
>CC: amsat-bb@AMSAT.Org
>Subject: Re: [amsat-bb] AO-40 70cm antenna side lobes?
>Date: Wed, 12 Dec 2001 08:55:51 -0700
>
>Wow, my name in actual print....kind of.
>Greg, FWIW:
>I could hear myself very well as well.  For reference:
>	Uplink 9el v-pol yagi with about 40W delivered to antenna.  Don't
>recall what I was running at the time but it wasn't full tilt.  U-band,
>no L just yet.
>	Downlink 2' solid dish, 2-1/4 turn helix feed, DEMI d/c.
>Don't know if you tried calling in CW...as I mentioned on the air, I
>could just barely barely make out that someone was calling.  But several
>CW tuning swishes were very loud; don't know if you were one of them.
>So...if you were one of them, perhaps your audio levels are way
>down/undermodulated?
>The squint wasn't too awful, around 12-15 degrees or so?  I would think
>the U-band antenna would be significantly lower gain/higher beamwidth
>such that squint wouldn't affect it as much.
>
>
>"Greg D." wrote:
> >
> > Hi folks,
> >
> > We've talked about the side lobes on the S2 antenna, where there is
> > significant energy squirting out at around 30 degrees.  I'm hearing
> > the beacon right now pretty well with a squint angle in the
> > neighborhood of 26 degrees.  MA is 209.
> >
> > But, I can barely get into the bird with 100 watts CW to 2x8 element
> > beam on 70cm.  Heard NX7U very clearly calling CQ, but couldn't get
> > back to him.  If you're reading this, nice signal!  I tried...
> >
> > I know that the off-pointed patterns of the various antennas are
> > different.  I'm guessing that the L band antenna has a lobe around
> > this angle, and the U band doesn't, and NX7U must have been on L.
> >
> > Is there any other angle, other than 0/0, where the side lobes of the
> > S2 Tx and 70cm Rx antennas line up?  I'd like to know when I have a
> > chance to get in.  Also, perhaps we could use them during the
> > upcoming hibernation period.
> >
> > 73s,
> >
> > Greg  KO6TH
> >
> > _________________________________________________________________
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