wrote in message
ps.com...
I am looking for plans to build some 70cm antennas for my handheld
radios. Cannot find much on the net. Has anybody on this forum built
their own, if so, how did they perform?
Any suggestions or pointers would be appreciated.
Cheers
Max
General rule: If you are willing to mess with an antenna for long enough to
get the VSWR nice and low at some freq, it will probably perform well.
http://www.mfjenterprises.com/produc...prodid=MFJ-842 is a VSWR meter
that will help you with that.
(
http://www.mfjenterprises.com/produc...prodid=MFJ-864 will do HF,
also -- perhaps a better buy than two separate units.) Not everyone likes
MFJ.
As to your antenna, what form will it take? How will you use it? Will it
mount directly onto the antenna jack on the radio or will it be on the end
of a length of coax? Up on a stick? Does it need to be directional, as for
service in the far boonies or for a t-hunt?
I have built several 70cm antennas, including two j-poles out of copper
pipe. I also built two ground-plane quarter-wave antennas; one was a
serious one for hoisting aloft with fishing line. The other one I built
directly on/into an old hard-hat as a novelty. I used a BNC panel-mount
jack as the basic structure of both of these antennas, with whip and radials
sprouting from the jack. I kept messing with the length, angle and shape of
the radials until I had a low VSWR. These antennas weren't tested under
extreme conditions, but they did a fine job on the local repeaters. (The
hard-hat antenna was operated on low power; why risk compounding the
existing "drain bamage"?)
If it needs to be super-light for portability, a wire j-pole out of #10 or #
12 AWG copper wire would seem workable. Feed it with a short length of coax
and you're golden. A j-pole out of TV-twinlead is also a possibility; I've
made a few for 2m, encapsulating them in PVC pipe, but never one for 70cm.
(I smell a project.)
http://cs.yrex.com/ke3fl/prgms/JPOLEFRM.HTM and click
j-pole calculations.
Look a some commercial designs and say, "Oh, I can copy that with a stick
and some coat hangers." You probably can.
"Sal"