On 10/18/2014 11:30 AM, Jeff Liebermann wrote:
On Fri, 17 Oct 2014 20:27:57 +0100, Brian Howie
wrote:

I was interested in the catenary problem for a different reason.
http://www.bigskyspaces.com/w7gj/longyagi.htm
I toyed with the idea of making one of those at one time.
Brian GM4DIJ

I built a "rope Yagi" like that for 2m long ago (1960 something).
Instead of 1/4" rod, I used #12 AWG solid electrical wire. I used it
as a hidden transmitter on a transmitter hunt where I pointed it down
a freeway. The signal was very strong on the elevated freeway, but
became extremely weak as soon as anyone left the freeway via an
offramp. It also had an impressive assortment of side lobes to
confuse anyone that got too close. We were eventually found, more by
luck than by technology or skill. A rope yagi has also been used on
very long range transmitter hunts. Mine was only about 20 meters long
yielding a theoretical gain of around 20dBi(?). Usable bandwidth was
very narrow (about 100 KHz as I recall) and difficult to tune
accurately. See antennas designed for EME for clues.

The antenna did droop badly in the middle. However, some crude
testing with extra ropes and poles in the middle didn't show much of
an effect on signal strengths until the elements were fairly close to
the ground. The only critical parts seemed to be the driven element,
reflector, and maybe the first 3 directors.

At some point in the past, I tried to do a model in YagiCAD or 4NEC2.
That's when I discovered that I needed an NEC4 calc engine to
correctly model it. Sorry, but no plot today.



LOL, that reminds me of a time I was the fox back in Iowa. I backed
into a school loading dock, surrounded on three sides by building. To
the west about ten blocks away was a large water tower (the type that
was a solid structure all the way to the ground - not a tank on a small
stem) in a large shopping mall parking lot.

I then aimed a pair of phased 11 element beams at the water tower.

The signal was quite strong in the mall, and hunters were all over the
place looking for me. Some started to head east, but the signal quickly
dropped off due to the rolling land (not real hilly, but hilly enough).
It took them over 4 hours to find me.

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Jerry, AI0K

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