I'm thinking of taking the insulator and center conductor from coax and
sliding it in and out of a copper tube, maybe with threaded rod to hold
position and facilitate fine adjustment. I'm figuring on copper tape on a
hula-hoop as the loop, with the cap mounted directly to the hoop, and
copper foil tying the sides of the cap to the loop so I don't have to
halve the capacitance with a dual-plunger reimplementation of the
butterfly. What kind of capacitance per inch can I expect? Would a 36
inch diameter loop at 5 watts make enough voltage to puncture rg-58?
rg-8?
If it'll take a lot of sliding, I'll have to switch to dual-plunger
to avoid excessive conductor length and flexing.

I plan to mount it on a backpack, using dowels, or maybe PVC, to elevate
it for a foot or so seperation from the metal pack frame - cap at
top(another reason to keep the cap light). Will tuning change a lot
depending on whether the pack is worn? I really don't want to have to add
motorized tuning so I can tune it while worn... weight, don't you know?

One other possible deviation - I'm considering carrying it flat. My width
will be unchanged, but it'll lower height by 18" or allow another 18" of
elevation, and give me an omnidirectional horizontally-polarized pattern,
right?

At 5W, I'm not concerned about heating, and even any RF burns should be
manageable, but I want to be as efficient as I can be within the
constraints of /PM operation.

If I can successfully build this, I'll try to document it well, and make
the design available to others. At the very least, maybe we'll get some
cool ideas.

73,

tim

Jim, NN7K wrote:
"---that center conductor of RG-8 was used as Power supply for lots of
AMPS! 3 and 4 KV in some of those."

Nothing wrong with that if the right RG-8 is used. RMS Max V varies from
600 V to 3700 V (Belden 9914). Peak a-c or d-c max V should be 5232 V
for the Belden cable. This is 1.414 X the rms volts. No need to
speculate. Coax tables abound. One is found in the ARRL Antenna Book.

Best regards, Richard Harrison, KB5WZI

On Wed, 06 Aug 2003 08:14:22 -0500, Richard Harrison wrote:
the Belden cable. This is 1.414 X the rms volts. No need to speculate.
Coax tables abound. One is found in the ARRL Antenna Book.

Good point - If I can get a dos or windows system up and running, I'll
model it with that magloop4.exe program. Regardless, I'd intended to pull
the center conductor back a half inch or so after stripping the cable to
the insulator. I actually intend to use rg-58 - smaller, lighter, and can
set the outer conductor closer to the center, for (I hope) higher
capacitance. I'm now considering mounting the sides of the cap to the
hula hoop with the hoop actually split there, so the hoop is stretched and
compressed as the capacitance is changed, to avoid tight flexure of
conductors or sliding contacts.

My biggest concern is dialectric puncture. I'll be running a maximum of
5W.

tim

Tim- at 5 watts, doubt that you could even puncture RG-174 (that the coax
about the thickness of 1/8 inch), that is used for test , and multiplex drop
cables! Jim NN7K




"Tim sent:
My biggest concern is dialectric puncture. I'll be running a maximum of
5W.

tim

"Tim Conway" wrote in message sethatanddropthis.com...
Good point - If I can get a dos or windows system up and running, I'll
model it with that magloop4.exe program.

Hi Tim,
Reg's programs run well in a DOS window of a Win2k system. Any system
from 386 to Pentium III should work for you.

BR from Ivan

On Wed, 06 Aug 2003 23:45:27 -0700, OK1SIP wrote:

Reg's programs run well in a DOS window of a Win2k system. Any system
from 386 to Pentium III should work for you.

Thanks, Ivan. I'm sure they do. I just don't have a working
microsoft-based system at the moment. I'm trying to get WINE up and
running, but my role as "Mr. Mom" keeps me from any long projects. It
took me two weeks to build a simple two-coil mobile HF antenna, just
because I can work on it for only a few minutes at a stretch.

One of these days, I'm going to have to move beyond just talking about it
and try to build one of these suckers.

73,

tcc