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Re: Arrow Mod



Hi David

Well I tried exactly what you suggested with two Arrows... ie, 7x7 on one
boom and 3x3 on the other. Drilled extra holes in one boom for the extra
70cm elements, using the other boom as a template. The 2m holes match some
of the 70cm holes.

Spent several evenings trying to get the darned things to SWR OK, with all
sorts of antenna analyzer techniques.

I could get the 70cm to tune in... sort of. Horrible narrow bandwidth and
about three different narrow resonances despite long hours adjusting the
gamma matches.

The 2m antenna just wouldn't do anything sensible.

I tried terminating one antenna whilst adjusting the gamma match of the
other. This seemed great until I started to use a power splitter and phasing
lines. As soon as I switched polarization, all the careful setting up went
AWOL.

At the end of the day, I failed. I'm guessing that either the antennas
couple badly, or my antenna range (my kitchen for the most part) upset the
configuration.

So my fix for this was to use the pair in the original 2/70 configuration,
place both of them on one fiberglass cross boom and switch polarization (see
http://www.btinternet.com/~hlong/ultimate_arrow.htm where there's some
pics).

The problem of offseting the antennas like this is that you tend to suffer
more from squint angle problems, and I quite often have to switch
polarization during a pass (esp. on 70cm).

However, it's a world better than the omnis I used to use.

If anyone's managed to perform the 7x7 / 3x3 config successfully I'd love to
hear about it!

73 Howard G6LVB

----- Original Message -----
From: "David M. Tipton, PhD" <tiptond@psi.com>
To: <amsat-bb@AMSAT.Org>
Sent: Sunday, October 15, 2000 6:30 PM
Subject: [amsat-bb] Arrow Mod


> I was sitting here this morning wondering if it would be possible to
> convert the Arrow design into 2 CP yagis on the one boom.  Could the
> additional elements be offset by 45 degrees?  Thus making it a 6 Element
CP
> Antenna on 2M with elements at 0/90/180/270 Degrees and 14 Elements on
70cm
> at 45/135/225/315 Degrees?
>
> I'm simply thinking about camera/tripod use.  This would provide a heavy
> (But not unwieldy) Mode J Antenna that would just about be the ideal for
> portable applications.  Would this be enough seperation, or would it cause
> too many problems?
>
> Dave, N8KXA
>
> ----
> Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
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>

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