Since K7LXC brought it up let me offer at least part of
the story of NK7U's 2x2 echelon stack. I came in on the
end of the story so I don't know all the details and
history.
I have been operating contests at Joe's stations in Baker
City, OR. for the last 5 years and have used the echelon
stack. I say stations because the antennas of interest are
no longer in the air. Joe moved 3 years ago and took down
the stack -- and is not planning on putting it back up.
The reason will be clear later.
At Joe's old QTH he did in fact have a 2x2 echelon stack
fixed on JA for both 10M and 15M. If I remember they were
all 5 element antennas. (We took them all apart last
summer, I just can't remember. With that much aluminum you
lose track. The 10M antennas may have been 6 element.)
These antennas were mounted 2 high and 2 wide on two
separate towers. So, each tower had 2 10M and 2 15M
antennas in a single vertical stack. They were fed with a
single feed system, operating them in phase. Note that the
top antenna in on each tower was fairly low. If I remember
the top 15M antenna was at 75' or so. The tower spacing
I'm sure was set for some specific distance but I can't
remember. It feels like it was one wavelength on 15M.
The original design objective of the stack was not so much
the horizontal narrowing of the resulting pattern, as it
was being able to get increased gain at a fairly high
takeoff angle. As beautiful as NK7U's old QTH was, it was
tucked up against the hills and the takeoff angle to JA
was, I think, in excess of 10 degrees. So, Joe had to get
his signal up fast, and the way to do this is with low
antennas. Kind of like optimizing an antenna system for
Sweepstakes. Joe would prefer to use 4 stacks on a single
tower, as he does on his Europe stacks, but in this case
it did not make sense. Such a stack would send its gain
right into the side of the hill.
I used the echelon in a couple of contests during the high
sunspot years and it was a joy. My favorite memory was
asking a JA one night what my honest signal report was. He
said, "59+20". I then asked what antenna he had. He
replied and then asked what I was using. I said a "2x2
echelon array of 5 element beams fixed on JA for a total
of 20 elements." All I heard come back over the airways
was rolling laughter.
But, all this is in the past now. At Joe's new QTH he has
no takeoff angle problems to JA. The same antennas will be
rebuilt this summer and configured in a more traditional 4
high stack. It would be interesting to consider an echelon
again, if we really wanted to concentrate a signal just on
JA. It is a fairly small target area and an echelon gives
you both horizontal and vertical pattern gain. However, it
would sacrifice the pattern to other Asia and Australasia
locations. At this time all we want to do is get all the
15M and then 10M beams back up. And, if anyone wants to do
some tower and antenna work this summer we could always
use an extra hand.
Speaking for the NK7U contest crew....
Scott/K7ZO
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
|