The VSWR of the 4 square, when adjusted, will depend as much on your
feed/phasing network as on the mutual impedances of the elements. When you
measured, were the feed lines disconnected at the shack, or at the
feedpoint? The usual way to measure mutual impedances is to measure the
impedance of an element (at the feedpoint) with the other elements open, and
shorted, one by one. Then a fair amount of algebra can get you to the actual
mutual impedance array. (ON4UN's book has procedures)
Do you know if the impedance is above or below 50 ohms? and, is it reactive
or not? An ideal resonant monopole above a perfect ground plane will have
a feed point impedance of 36 ohms. 10-20 of ohms of loss resistance (which
isn't all that unusual) can bring that nicely up to 50...
Jim, W6RMK
----- Original Message -----
From: "PY2YP" <py2yp@pobox.com>
To: <towertalk@contesting.com>
Sent: Monday, June 16, 2003 5:46 AM
Subject: [TowerTalk] Adjusting a 4 square
> Hello,
>
> I do have a problem that, due to a lack of knowledge, I can't find the
> solution.
>
> I did measure the 4 towers of my 4 square when they were not phased, e.g.
> them all were disconnected, and fed each one at a time to found out the
> following VSWR values:
>
> Tower 1: 3.800 1:1.41
> Tower 2: 3.800 1:1.59
> Tower 3: 3.800 1:1.54
> Tower 4: 3.800 1:1.48
>
> I have a spreadsheet (57 kbytes) with the complete measured values and a
> graph as well.
>
> All towers have an aluminium tube at the end which allows to either make
it
> shorter or longer. The question is: based on these values how long do I
have
> to increase each one, e.g., towers numbers 2, 3 and 4, in order to have
them
> all set to the same VSWR value, I?d say 1:1.41.
>
> As far as I know the 4 towers when phased will have low VSWR values due to
> the mutual impedance. Am I right?
>
> Thanks in advance for any help.
>
> 73 DX de PY2YP - Cesar
> http://www.qsl.net/py2yp
> py2yp@pobox.com
>
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
|