[Antennas] Wire Antenna Questions/Opinions

2002年11月07日 12:55:00 -0600

I use a parallel-coax balanced line made of two runs of RG-213. Shields are
tied together at each end, floated at the ladderline end and connected to
the tuner chassis at the input end. Zo is 100 ohms so SWR can be higher
than ladderline SWR, of course. 
I use 213 to take advantage of its high voltage rating so that voltage
peaks in the standing wave do not cause internal arcovers. Of course, with
95% of my operation at 5 watts, this is not something that I really worry
over! <:}
The only requirement on the coaxes is that they be of the same length. They
do not have to be spaced or even run together just so the shields are
handled as described above. The line Zo does not depend upon the physical
spacing of the two coaxes, but rather is determined by the Zo of each line,
which is fixed.
My line is brought into the shack via the attic along with several other
single coaxes.
This setup is described in most ARRL Antenna Books and Handbooks.
73/72, George 
Amateur Radio W5YR - the Yellow Rose of Texas
In the 57th year and it just keeps getting better!
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
K2 #489 Icom IC-765 #2349 Icom IC-756 PRO #2121
"Dennis L. Wade" wrote:
>> I agree, that is a good rule of thumb. However, my concern is
> keeping the balance of the feedline through its transition into the
> shack, and therefore keeping alot of RF out of the shack.
>> In this case, the balun and tuner would be separated by no more than
> 20 feet of RG-8 type coax.
>> I'd like to bring in the open wire line right to the balun at the
> tuner, so I'd like to hear suggestions about how to do that. Note
> that there will be actually two open wire feeders to bring in.
>