Team
I have had similar experiences as Paul and I agree with everything Paul has
said.
I would only add that it has been my experience that if I use the standard
Comtek recommended phasing line configurations and the Comtek switching box
and I individually resonate each of the four individual vertical elements
and their radial pairs to a resonant frequency of approximately 3.6 MHz that
the entire ensemble in operation for me resonates at approximately 3.8 MHz.
Bottom line...the ensemble resonant frequency for me has always been higher
than the individual resonant frequencies of the individual verticals and
radials....but this is using the standard Comtek switching box and feeding
recommended by Comtek for a four square 75M steerable phased array.
My experience has been that a steerable vertical four square array for 75M
or 80M with elevated radials *really* works well with the base of the
vertical and the radials elevated at approximately 20 feet above ground and
that the difference in performance between the array and a single vertical
or an elevated dipole or an inverted V is frankly *unbelievable*
until/unless you experience it. Well worth the effort. Enjoy!
73, Ted, K6XN
Ps FYI, we are installing another four square 75M steerable phased array up
in the Sierras in a wilderness area in Nevada County, California, on top of
a 5000 foot mountain in the middle of a forest. We are using two guyed ten
foot Rohn 25G sections to elevate each vertical (eight Rohn 25G sections in
all) and we are using four modified Butternut HF-2V vertical antennas...plus
the Comtek phase shifting box etc. We hope to have the ensemble operational
in time for the California QSO Party (CQP) in October. Everything is on site
but some chain sawing, concrete mixing and assembly is still needed. The
rattlesnakes on site have not been amused to date :-)
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Paul Playford
Sent: Wednesday, June 28, 2006 9:08 AM
To: Dino Darling; Jim Lux
Cc: towertalk@contesting.com
Subject: Re: [TowerTalk] Portable Phased Arrays!
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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