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Hal Rosser · December 25th 07, 05:10 AM posted to rec.radio.amateur.antenna

"J. Mc Laughlin" wrote in message
...
Dear Antenna Group: Here is an antenna question. December 24, 2007

On the cover of the Winter 2007 QCWA Journal one may see three pictures of
antennas used by Collins Radio. Two of the pictures feature a circular
array of six curtain antennas. In other words, the array is expected to
effect six beams - one every 60 degrees.

The curtain part of the array is straight forward. The six antennas that
are in front of each curtain are new to me. It is my hope that an
explanation will be forthcoming about how the front antennas "work."

Curtain description: Six, triangular, lattice towers of uniform cross
section are placed equally on the circumference of a circle and guyed in
four places. At least 52 (equally spaced in a vertical plane) horizontal
wires are stretched between adjacent towers and the horizontal wires
appear to be insulated from the towers at their ends. No noticeable sag is
seen. A crude estimate suggests the towers are something like 80 to 100
feet high.

Front antennas: 17 horizontal doublets, all of essentially the same
length, and all in a vertical plane that is parallel to the associated
curtain emanate from a tubular mast placed in front of each curtain. [It
is well known to place fat, horizontal dipoles in a broadside
configuration in front of a curtain consisting of horizontal wires. At
least part of the Collins' array does not look like anything I have seen
before.] What I see has mirror symmetry with respect to a doublet that is
in the middle of the mast. I assume that the antenna is fed with a
balanced transmission line connected to the middle doublet. Above and
below the middle doublet is seen exactly the same collection of doublets
fed with a balanced transmission line..

Starting with the middle doublet and proceeding upward a distance that I
call 3X, one encounters a collection of seven, equally spaced doublets
(spaced X apart). The bottom of the group of seven is seen to be fed with
a balanced transmission line coming from the middle doublet. A balanced
transmission line is seen emanating from the top doublet of the group of
seven for a distance 3X to an isolated doublet at the top of the mast.

If one were to ignore the groups of seven (one above the middle doublet
and one below the middle doublet) one would have an antenna of three
doublets in broadside with the likelihood of 1:2:1 factors so as to
minimize lobes. The groups of seven could comprise two "elements" in
broadside. Here is one additional fact about each group of seven: while
the top and bottom doublet (of each group of seven) clearly have an
attached balanced transmission line (one comes from the middle doublet and
the other goes to a distal, solo doublet), the group of seven appear to be
connected by a "butterfly" of what may be mesh (because one can see
through the butterfly).

The butterfly is simple, but not easy to describe. It is two isosceles
triangles with their bases vertical and outward from the mast, and with
the apex of each triangle appearing to touch the mast at the middle
doublet of the group of seven. I estimate the height (base to apex) of
each half to be about X. I assume that the mesh of the butterfly is
connected to each of the doublets of the group of seven.

So, who might be able to explain this?

73, Mac N8TT
--
J. McLaughlin; Michigan, USA
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Sounds like a good antenna to try - except the XYL will really make herself
an "ex" after seeing the array. Some of those XYLs just don't understand!