On Wed, 16 Mar 2005 12:51:17 GMT, "tom" wrote:

If you really needed to get a 2m rig on the air and you didn't have an swr
meter, do you think you could get way with creating a simple dipole if it
was VERY carefully cut according to the formula, and if you wound your own
impromptu balun out of 5-6, 4" diameter turns of the (RG-8)cable right below
the dipole? Even if the resonant frequency wasn't exactly in the middle of
the 2m band, how much damage to the rig would you be risking? I don't see
how it could do any serious damage, even if the swr was somehow slightly in
excess of 2, or is it just something that is never, ever done --- not
checking the swr first with a meter? According to the antenna books I'm
reading, 1/2 wave dipoles (where each radiating element is 1/4 wave) don't
need fancy matching transformation stuff, the only issue might be RF coming
back through the outer braid and causing the cable to radiate --- thus the
5-turns-on-the-cable balun.



What you're proposing should work fine. For each quarter wave element,
length in feet = 234/frequency
or
length in meters = 71.4/frequency

So each quarter wave element would be around 18 or 19 inches,
depending on where you want to be in the 144-148 mhz range. The
formula should get you close enough to keep from blowing up your rig.

Coiling the coax as you propose shouldn't hurt anything, either. Try
to bring the coax away from the antenna at a 90-degree angle, and
hanging the antenna vertically would help if you're trying to work
mobiles or repeaters.

Also, you might consider a ground plane vertical, attaching five
quarter wave wires to a female coax plug, one vertical wire, with four
radials in the holes on the ground side.

bob
k5qwg