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Re: [TowerTalk] 80m 4Square Dipole VSWR question

To: "Yo3ctk" <>,"Paul Playford" <>,"'D. Rodman, MD'" <>,"'towertalk'" <>
Subject: Re: [TowerTalk] 80m 4Square Dipole VSWR question
From: "Tom Rauch" <>
Reply-to: Tom Rauch <>
Date: Thu, 18 Nov 2004 08:08:48 -0500
List-post: <>
> I read from your comments that the Comtek box doesn't work
and cannot work.
> Is my reading correct?

No, I never said that. It's obviously a good system, many
people use it and have been using it for years.

My only point is people look at these systems and assume
they can take the classic base impedance of a lossless
vertical translated through 1/4 wl of coax and that is what
the box sees. That very obviously isn't true. Phased arrays
like this don't behave that way, unless they have terrible

 (To make everyone happy, if you add a great deal of loss
resistance the elements get very close to the same impedance
because the loss swamps out mutual coupling. Since most
people don't want that on transmitting arrays, I'll ignore

My points are only these:

The impedance of forward, rearward, and center pair elements
in a 4-square are all different. If you change the elements,
you can't simply recalculate based on the "dry" impedance of
one element.

The power fed to each element is different. Current fed
antennas require equal current in each element, voltage fed
antennas require equal voltages to produce a deep null and
near-maximum gain. If the pattern desired is a classic
pattern, the power to the element ports (the center element
feed pair are the same) is obviously significantly

A lack of heat in the dump resistance of a hybrid really
does not tell you the array is behaving like you might think
it is.

Consider the case where people insert coax in series with a
feedline to "phase" an array. Unless that coax is an exact
multiple of 1/4 wl, the electrical length of that cable will
not equal the phase delay unless the cable is terminated in
its surge impedance. Very few people who have 1/8th wave
spaced antennas with 3/8th wave coaxial delays actually have
135 degree delay like they think.

Those are the only points I'm making. I have no idea how the
Comtek box works because I've never owned one. I only know
how phased arrays and phasing systems work.

Maybe someone has characterized the Comtek box, and knows
what port terminations it likes to see. Whatever it is, it
probably is not the uncoupled impedance of the elements
transformed by the 1/4 wl cable.

73 Tom


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