I have experience with 4 square phased arrays. Over a dozen so far.
The advantage of parasitic feeding is simplicity.
I erect the 4 elements with elevated radials in their calculated positions
(.22 wavelength on a side). Then I take two of the radials that run in
opposite directions, feed them as if they were a half wave dipole and trim
them to resonance. Then I adjust all of the other radials to that length.
Then I trim one of the vertical elements for resonance against it's
counterpoise, and adjust the remaining vertical elements to the same length.
That completes the antennas.
Then I cut 4 pieces of 52 ohm coax to 3/8 wavelength electrical. These
coaxes become the feeders for each vertical element.
The array is fed through 1 of these cables, the far ends of the other cables
hang free, are not terminated, and make their respective elements inductive,
which make them look like reflectors to the driven element. These 3 cables
can be coiled up and hung below their respective feed points, just keep them
away from metalic objects or the ground.
The disadvantage is they are not broad banded. One array will not cover
both 80m and 75m, but one array will cover all of 40m.
And the same parasitic concept can be used with more or fewer elements, and
will work with dipoles as well as conventional ground plane arrays.
My current 40m and 80m 4 squares use Comtek phase shifting boxes, 4 elevated
tuned radials under each element, and work very well. Using the phase
shifting box the 80m array even works fairly well on 75m.
Have fun with your project.
de Paul, W8AEF
----- Original Message -----
From: "Jim Lux" <jimlux@earthlink.net>
To: "Paul Playford" <paul@w8aef.com>; "Dino Darling" <dino@k6rix.com>
Cc: <towertalk@contesting.com>
Sent: Wednesday, June 28, 2006 6:53 AM
Subject: Re: [TowerTalk] Portable Phased Arrays!
> At 10:26 PM 6/27/2006, Paul Playford wrote:
>>You may want to consider parasitic feed. That could simplify phasing a
>>bunch.
>
> Phasing is about the same regardless: you need an LC network for each
> element, and having active feed to all elements allows a bit more freedom,
> because you don't have to depend only on mutual coupling to excite the
> parasitic radiators. This is especially important when you have to
> tolerate arbitrary arrangements of the elements.
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