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.





--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558