Bill wrote:
I have built several coaxial dipole antennas in the past with great
success. What I like about this antenna is it is broadbanded. If you
design it using the center of the band of your interest, for the most
part you can cover the entire band without retuning. The problem I
have always had with this is the antenna is somewhat fragile. I have
used plexiglass squares to secure the center of the antenna and taped
nylon fishing line to the legs for more strengh. Any one with more
ideas? These are mostly useful in the HF range. You can find the info
on designing these at http://www.amateurradios.info and other places
on the net.

73's
Bill w5grx

Hi Bill,

I use 4 wire cage designs for 80m (as an inverted vee) because bandwidth is
inverse to the length/diameter ratio, and a single wire has a bad L/D on the
lower frequency bands. A single-wire 125' dipole made from #14 (0.071" OD)
has a L/D of over 20000:1 while a 4-wire 24"x24"cage (effective dia = 8")
has a L/D of 190:1.

If cut for the middle of the band, VSWR is just a touch over 2:1 at 3.500 &
4.000 MHz. I make spreaders from 1/2" thinwall PVC tubing & crosses
(24"x24"). I use #14ga 168-strand soft-drawn copper wire but smaller wire
could be used w/o much sacrifice in strength. A handy online calculator is
he http://www.smeter.net/antennas/dipcage2.php

A few photos of my home QTH antenna: http://tinyurl.com/2puwx5, the apex at
about 50' in a tree. A bunch of photos of my latest FD setup:
http://tinyurl.com/38v9wn, the apex at 35' on a homebrew tilt-up/rotatable
mast. I use a choke balun at the feedpoint. All parts came from Davis RF:
http://www.davisrf.com/ because they have good prices and stock my preferred
compression insulators.

Vy 73,
Bryan WA7PRC

I use 4 wire cage designs for 80m (as an inverted vee) because bandwidth is
....[snip]....
has a L/D of over 20000:1 while a 4-wire 24"x24"cage (effective dia = 8")...

I'm curious why a 2-foot-square cage has an effective diameter of only 8"


If cut for the middle of the band, VSWR is just a touch over 2:1 at 3.500 &
4.000 MHz. I make spreaders from 1/2" thinwall PVC tubing & crosses
(24"x24"). I use #14ga 168-strand soft-drawn copper wire ....

Doesn't soft-drawn copper stretch like mad?

--
--Myron A. Calhoun.
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge
NRA Life Member & Certified Instructor for Rifle, Pistol, & Home Firearm Safety
Also Certified Instructor for the Kansas Concealed-Carry Handgun (CCH) license

Myron wrote:
I use 4 wire cage designs for 80m (as an inverted vee) because bandwidth
is
....[snip]....
has a L/D of over 20000:1 while a 4-wire 24"x24"cage (effective dia =
8")...

I'm curious why a 2-foot-square cage has an effective diameter of only 8"

It's apparent to me that it can't appear that large because it's 4 strands
of 14ga wire instead of a 24" diameter cylinder. I obtained the 8" figure
from the calculator program at: http://www.smeter.net/antennas/dipcage2.php.
I don't know how the effective diameter was calculated.

If cut for the middle of the band, VSWR is just a touch over 2:1 at 3.500
&
4.000 MHz. I make spreaders from 1/2" thinwall PVC tubing & crosses
(24"x24"). I use #14ga 168-strand soft-drawn copper wire ....

Doesn't soft-drawn copper stretch like mad?

I was told by the CSR at Davis RF that it's soft-drawn but I expect it's
hard-drawn -- an unscientific stretch test in my workshop appears to confirm
this. Over a 12 month period, a 12ga single-wire 80m dipole (with choke
balun & RG58 feedline) did not noticeably stretch. Also consider that in
my case, the cage dipole is in inverted vee form, so there's no concern
about wire stretch caused by the heavier LMR400 feedline & balun weight.
Also, it's 4 strands of 14ga wire instead of one, and the spreaders don't
add much weight.

--
--Myron A. Calhoun.

Bryan WA7PRC