I did a google on "twin lead antenna" and found this.  There is nothing
magic about this antenna, I've built many and they work great and it doesn't
really matter what kind of coax you use.

Read on below - Regards -Ken -N5SWR

http://hamgate.sunyerie.edu/races/antenna/pocket.htm

Pocket J-Pole Antenna for 2 Meters
The following is a description of a J-Pole antenna made from 300 ohm TV
twin-lead. They have quite a few advantages which include improved
performance for
HTs, portability, and low cost.

For a center frequency of 146 MHz:

1. Start with @54" of TV twin lead (flat, NOT foam core)
2. Strip 1/2" of insulation at bottom and solder wires together.
3. Measure 1 1/4" from soldered wires and strip insulation on both sides.
This is the solder point for a coax feedline.
4. Measure 16 3/4" from coax shield solder point and cut out 1/4" notch.
5. Measure 50 1/3" from coax center conductor solder point and trim off twin
lead at that point.
6. Feed with a length of RG58U coax. Tape coax at feedpoint to the twin lead
for strength and seal coax for weather protection.

To get the best possible match, in step three above simply MARK the "solder
points" and measure from the mark for step 4 and 5. Now solder straight pins
to your conductor and your shield. Insert the pins at the marked point and
test for VSWR at the design frequency (146MHz).

If necessary, probe up or down till you reach 1:1 (close as possible).

Solder at the best points. To try this, you may want to start with the twin
lead a little long and trim down to resonant length - note: you'll need to
trim
in a 3:1 ratio to maintain the 3/4 to 1/4 wave.

It has been noted that this design can lead to rf coupling onto the
feedline. To avoid, put ferrite beads on the coax at the feedpoint, or use
3-5 turns
of coax (1"-2") taped together at the feedpoint.

You may attach an alligator clip to the plastic on the top of the antenna in
order to easily hang it. Alternately, punch a hole near the top and use a
length
of fishing line to hang.

This design appears on many BBSs, in club newsletters, and in books; the
earliest reference that I know of is a Jan. 1984 D.A.R.C. antenna article by
James
Burks, KA5QYV. This antenna is relatively broad-banded and will be more than
adequate if simply built as noted in steps above.


...artical continues ....

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