[TowerTalk] G5RV

[Charlie Ocker]

Bill, AS4LR, writes:

> Open wire has less loss, but is troublesome to bring into a building. For 
> years I've run transmitting twin-lead to the house, then switched to a 
> balun with a short run of coax to the shack. Use only solid dielectric 
> coax (RG-8)! Sure, foam dielectric has lower losses, but substantial 
> voltages can be present in the coax in this "unmatched" configuration. 

Another way to do this is to use a short run of shielded parallel line.  The 
ARRL Antenna book describes this better than I can, but in essence it is two 
equal lengths of coax with the shields connected together at each end.  Insulate 
the shields with tape or rtv.  Tape the line together every few feet to keep it 
parallel.  This line will have a different Z than the rest of the parallel line 
you're using, but it can be brought into your shack directly.

Big problem with using a balun at the output of a tuner is that baluns really 
only like to work into known resistive loads.  If the load is reactive, such as 
is usually the case at the end of a run of parallel line (open wire, ladder, 
etc.) then you can't really be sure that the balun is going to work properly.

You want to insure that your feedline remains balanced.  Kinda tough to do if 
your balun isn't doing it's job correctly.

Much better to put the balun at the input of a BALANCED tuner.  Rich Measures, 
AG6K,  wrote an excellent article on this subject in the February 1990 issue of 
QST, starting on page 28, entitled "A Balanced Balanced Antenna Tuner".  Check 
it out... good reading and makes sense.


73 es gl,

Charlie  N9CO	ocker@chasind.com

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