[TowerTalk] 4 Square phase line length question

[Jim Lux]

----- Original Message -----
From: "Tom Rauch" <w8ji at contesting.com>
To: "Jim Lux" <jimlux at earthlink.net>; "Dan Levin" <dan at andlev.com>;
<towertalk at contesting.com>
Sent: Saturday, May 08, 2004 7:23 PM
Subject: Re: [TowerTalk] 4 Square phase line length question


> > Here's the interesting thing..I assume you're using some
> scheme where you
> > use 1/4 wavelength lines for current forcing, right? so
> the element current
> > will be what it should be, regardless of the element
> impedance.  The
> > mismatch at the feed eventually winds up back at the
> hybrid/phasing network,
> > where you can take it out by changing the L or C of the
> phasing network (or,
> > just ignore it, and take it out at the array feed point).
>
> Forcing equal currents requires equal input voltages and
> correct input voltage phase. 1/4 wl away that becomes equal
> currents and with correct current phase.
>
> The hybrid does NOT provide equal voltages at the output
> ports, and it requires matched loads for predicted phase.

However, it's presumed that one could adjust fewer components in the hybrid
to compensate for the band change than fiddling with each element.  If you
use an approach like a 90 degree T or pi network for the phase shift, then
you've got three components to fool with, so you can transform not only
phase but voltage (i.e. impedance). One could either switch between two
networks, or use some tapped/adjustable components.

For that matter, if the frequency is a big percentage change, then the
phasing lines aren't going to be 1/4 wavelength long, regardless of the
notional element impedance.

>
> Fortunately the 4 square is somewhat forgiving of errors.


>
> 73 Tom
>
>
>