"Rick" wrote in message
...
In the spirit of trying to get something going on the subject of
antennas, and away from all the off topic posts......

Are you doing anything interesting with antennas? Putting anything up
new for the contest season? Learn something new that the rest of us
might benefit from hearing about, even if it isn't patentable?

For me, I have become interested in rhombics and am currently building
one. It was based on the one featured in the ARRL Antenna Book, which
is 377 feet long (right down the middle) and 210 feet on each side.
210 feet is 3 wavelengths on 20 meters. So far I have learned a
little about the rhombic. It can be built as a terminated rhombic or
a "resonant" rhombic. In the case of a terminated rhombic, you
install a 600 ohm resistor at the far end, and that absorbs the power
that would otherwise be radiated off the back, making the antenna
uni-directional. Another advantage is, the feedpoint Z is
approximately flat and equal to 600 ohms across a huge frequency
range. So the antenna has gain and lots of it, at least over the
range of 20-10 meters and everything in between! If you don't
terminate it, it works the same way in the forward direction but has
no front to back. And the impedance varies all over the place. But
does anyone have a 600 ohm resistor they could supply me with? 300
watts or so? Noninductive.

So getting down to practical details, here's some of my experiences so
far. Copper wire has gotten very expensive. #14 stranded down at the
local Depot store is now 8 cents a foot, #12 is 14 cents. That adds
up fast when you need 840 feet of the stuff. So I managed to find a
roll at 900 ft on eBay for about 60% of that and got it. Now the
problem with #14 is it sags. Well maybe not, maybe it is the rope
holding the end up, it is very hard to pull up 200 feet of wire and
get it to where it doesn't look like the suspension cables on the
Verrazano bridge.

Ok so now how to get the rope up high enough in the oak to make it
useful? Bought a slingshot. For-get-it. I tried bolts, nuts,
fishing weights, etc, can't get the damn thing with fishing line to
get over 16 feet and most of the time it tangled the line and
sometimes actually ended up behind me. Crosman Slignshot for sale,
$25 shipped to your door. Here's what works for 25 feet.... get xyl
to climb a ladder in the back of the pickup parked beside the tree.
She takes a tennis ball with light dacron rope taped to it and throws
over the branch while I shout encouragement from below. It works.
(oh, by the way, xyl is KC2PRW). That's the good news, the bad news
is 25 feet ain't high enough, with the sag problem mentioned above.
Next, get bow and arrow from neighbor, yeahhhhh !! that works. Now
got line over 35 feet, that's decent. Same success on 2nd tree. Now
got the feedpoint tree and one of the corner trees with nice lines up
35 feet. Now pull up the wire and notice that the smallest little
friggin branch in the oak trees will snag the #14, so get the ladder
and trim off dozens of those little suckers. So that's where we are
at the moment. I figure about 50% done. Now the question is, will it
work?

I found (google can find anything) a great circle bearing program that
told me to point it 47 degrees which, from New Jersey puts me right
over London and down into central Germany. Look out DLs. According
to my antenna modeling program it will have 14 dbi gain and a 3 db
beamwidth of 20 degrees. Man that is sharp, much sharper than any 3
element beam. What's with these dbi's ? For comparison, a 3 ele beam
at 70 ft will have 12 dbi gain. The rhombic at 30 ft has its main
beam at about 22-25 degrees elevation. I sure wish I could get it up
to 70 ft, but there's no chance.

So now I have to get two more trees rigged with ropes and then get
down to the business of feeding the monster. I will be using balanced
ladder line to a homebrew tuner which I haven't built yet.

If I get any positive feedback on this post I will continue with my
progress and maybe even provide some on-air results in a week or so.

So that's my story. What are you working on?

Rick K2XT

I'm not working on anything at the moment, Rick. But, your post is the best
I've seen in quite a while and it makes me want to get up off my butt and do
something. Thanks for that!

I look forward to more info on your project.
73,
John