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
Home:

"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
Home:

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!

On Mon, 24 Dec 2007 11:36:52 -0500, J. Mc Laughlin wrote:

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.

Is it something like this?

http://www.kk5im.com/hamimages/bboard.jpg

Dear Tehrasha Darkon and Group:

Yes! An additional curtain antenna is seen off to the right of the picture,
which somewhat confuses. Additionally, the butterfly is not easy to see on
the nearest antenna. Thank you for finding the picture.

Now, if the actual antenna people who have been on this group have not been
driven off of the group by the theological ramblings about whether angels
exist and, if so, how many could fit on the head of a pin, please enlighten
this old antenna person who had thought he had seen every practical antenna
(including a good many that were not practical - see US patent 1,554,231).
What is the function of the groups of seven + butterfly?

73, Mac N8TT

--
J. McLaughlin; Michigan, USA
Home:

"Tehrasha Darkon" wrote in message
news
On Mon, 24 Dec 2007 11:36:52 -0500, J. Mc Laughlin wrote:

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.

Is it something like this?

http://www.kk5im.com/hamimages/bboard.jpg

"J. Mc Laughlin" wrote in message
...
Dear Tehrasha Darkon and Group:

Yes! An additional curtain antenna is seen off to the right of the
picture, which somewhat confuses. Additionally, the butterfly is not easy
to see on the nearest antenna. Thank you for finding the picture.

Now, if the actual antenna people who have been on this group have not
been driven off of the group by the theological ramblings about whether
angels exist and, if so, how many could fit on the head of a pin, please
enlighten this old antenna person who had thought he had seen every
practical antenna (including a good many that were not practical - see US
patent 1,554,231). What is the function of the groups of seven +
butterfly?

73, Mac N8TT

--
J. McLaughlin; Michigan, USA
Home:

Hi Mac,

I have not build those monsters but examining the picture, what it looks
like:
The six towers in circle seem to be support for the reflection screens, with
wires stretched between them from top to bottom.
In the middle of each section and on the front of the screens is the tower
with sets of two broadband arrays, which should allow some vertical beam
steering, like a stack of two antennas. So six direction and some vertical
beam steering with great F/B thanks to reflector screens.
On the right there seems to be the classic curtain array with reflectors.

Most of the guys on this group know everything about antennas, lossless
lines, just don't have much in their backyards. :-)

Dear Yuri:

Indeed. See my original posting for a discussion of a circular, curtain
array.

Your idea of some vertical beam steering is interesting. That would
require adding or subtracting phase to one of the two sections. The picture
seems not to show means to perform this bifurcation. The middle doublet has
a parallel transmission line going from its middle both upward and downward.
Of course, a switching means could be hidden by the mast.

What continues to puzzle me is the use of the two groups of seven
doublets that seem to be connected by a mesh butterfly. It may well be that
those groups of seven serve the same function as conventional, fat-dipoles
in front of a reflector screen.

Unfortunately, my dedicated computer used for modeling died. It had an
Intel board that had been stuffed with defective capacitors and only lasted
four years. Its replacement (P4 3.2 GHz + 3 GB of memory) has yet to be
brought up to speed (something is holding down its performance) - waiting
for son's help. In short, I have yet to model the group of seven +
butterfly.

Thanks, 73 Mac N8TT
--
J. McLaughlin; Michigan, USA
Home:
"Yuri Blanarovich" wrote in message
...

"J. Mc Laughlin" wrote in message
...
Dear Tehrasha Darkon and Group:

Yes! An additional curtain antenna is seen off to the right of the
picture, which somewhat confuses. Additionally, the butterfly is not
easy to see on the nearest antenna. Thank you for finding the picture.

Now, if the actual antenna people who have been on this group have not
been driven off of the group by the theological ramblings about whether
angels exist and, if so, how many could fit on the head of a pin, please
enlighten this old antenna person who had thought he had seen every
practical antenna (including a good many that were not practical - see US
patent 1,554,231). What is the function of the groups of seven +
butterfly?

73, Mac N8TT

--
J. McLaughlin; Michigan, USA
Home:

Hi Mac,

I have not build those monsters but examining the picture, what it looks
like:
The six towers in circle seem to be support for the reflection screens,
with wires stretched between them from top to bottom.
In the middle of each section and on the front of the screens is the tower
with sets of two broadband arrays, which should allow some vertical beam
steering, like a stack of two antennas. So six direction and some vertical
beam steering with great F/B thanks to reflector screens.
On the right there seems to be the classic curtain array with reflectors.

Most of the guys on this group know everything about antennas, lossless
lines, just don't have much in their backyards. :-)

On Thu, 27 Dec 2007, J. Mc Laughlin wrote:

Yes! An additional curtain antenna is seen off to the right of the picture,
which somewhat confuses. Additionally, the butterfly is not easy to see on
the nearest antenna. Thank you for finding the picture.

The circular array is the Collins Billboard, it covers 9 thru 27MHz, and
is phase steerable thru 360 degrees. The general rumor is that there are
only 2 of them in existance. The one in the picture here in Ceder Rapis
and an identical array belonging to SAC.

The array behind and to the right was a pair of panels for 3 thru 6 Mhz.
They were taken down in 1996.

I am not sure how much longer the circular array will be up and
operational. The antenna farm here at Collins has been significantly
reduced by the addition of new buildings to the campus. We have already
given up a couple of smaller directional arrays and one of the big
log-periodics.

--
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