David G. Nagel wrote:
Your best choke is about 30 feet of coax rolled up into a 12" coil.

Seems to me, the best choke(s) would be two chokes, one designed
for 75m-15m and the other designed for 12m-2m. I cannot bring
myself to believe that a coiled up piece of coax could ever be
an effective choke over a 40:1 frequency range.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
David G. Nagel wrote:
Your best choke is about 30 feet of coax rolled up into a 12" coil.

Seems to me, the best choke(s) would be two chokes, one designed
for 75m-15m and the other designed for 12m-2m. I cannot bring
myself to believe that a coiled up piece of coax could ever be
an effective choke over a 40:1 frequency range.
--
73, Cecil http://www.w5dxp.com

Why worry about VHF though? Most people wouldn't want to use
their HF wire for VHF. Or at least, I wouldn't. I always use other
antennas for those bands. Seems to me, if you were to use two
chokes, one for 160-40, or 80-30, and one for 20-10 would be more
practical. A good choke for 20-10 "tribander", is 8 turns of RG8 wound
on a 6 inch form. There is no real need to wind in an orderly military
manner,
although some do. I often just throw them together liking rolling up a
rope,
and they work fine. I had to place a small choke on my mobile for 2m.
I kept having problems tuning a 5/8 wave 2m whip I made a few weeks
ago.
Tried trimming, adjusting the coil, etc. No joy. Came to the conclusion

common mode currents were causing me grief, and this is using a hole
mount drilled in the trunk lid. I usually don't have problems with
those..
I wound a small coil from rg-58, maybe 4-5 turns on a small appx 2 inch
dia,
and all my problems were gone.
A coax choke will need to be pretty small to work well on VHF.
I don't really see one made to work the upper HF bands as being very
good. So, in designing one for upper HF, I'd use 30 mhz as the upper
limit. I've got some info somewhere, maybe in the ARRL ant book that
gives appx dimensions for chokes at various frequencies. 30 ft of coax
wound on a 12 inch from would more likely suit the lower bands more
than
the upper HF bands. So I'd use a 8 turn, six inch dia choke for 20-10,
and whatever choke for the low bands. I'd leave VHF out of it, being
most
HF wire antennas are fairly lame for VHF. Heck, on my 706mk2g, using an
HF wire antenna is inviting lots of image problems for receive when
using
6 meters. 2 meters, I use ground planes, yagi's, etc.. I use a 3 el
yagi on
6m.
MK

wrote:
Why worry about VHF though?

Because MFJ advertises 2m operation with the
recommended coil of coax?
--
73, Cecil http://www.w5dxp.com