RadioBanter - View Single Post

January 1st 06, 03:15 AM posted to rec.radio.amateur.antenna

wrote:
I wonder if u could help me, i have a tri-band beam erected and am
considering using 450 ohm feeder due to the less amount of loss on the
line (as opposed to RG58)

Matched line loss for 450 ohm ladder-line is indeed less than the
matched line loss for coax. But using ladder-line to feed a tri-beam
will result in an SWR on the ladder-line of around 10:1 so you will
be losing power because of higher SWR. If your coax run is less than
100 ft., I would just upgrade to a better grade of coax than RG-58.

The radio i am using is an IC-756PROII, with inbuilt ATU, will i be
able to connect the feeder direct to the beam and run it straight into
the back of my 756 (using 259 connector) ??

Or will i requrie a balun at either the beam or radio end???

To do what you want to do will require a choke-balun at the IC-756.
In addition, what you want to do will require you to feed the beam
with a multiple of half-wavelengths of ladder-line. That means you
will be required to change the length of the ladder-line when you
change bands in order to get an impedance that your IC-756 tuner can
match. To use such a system, you have to know exactly what you are
doing. I do use such a system myself.

If you don't want to change the length of your ladder-line when you
change bands, your best solution is probably to go with a good grade
of coax like RG-8, RG-213, or LMR-400.
--
73, Cecil http://www.qsl.net/w5dxp