On 4/25/97 12:07, Charlie Ocker at ocker@chasind.com wrote:
>Bill, AS4LR, writes:
That's A*A*4LR, thank you. (And I thought I only had this problem on the
air!)
>> 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.
This avoids the balun, but it has the same problem with potentially high
voltages, so use solid dielectric coax for maximum breakdown protection.
>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.
Depends on the type of balun (wouldn't a solenoidal air-core balun give
fewer problems?), but conventional toroidial broadband baluns could give
problems and are another potential site for a voltage breakdown.
I've been using a 2KW toroidial balun with a massive core, and I don't
run power (since I've never owned an amplifier). I've used this antenna
with good success at three different sites. Antenna even took a nearby
lightning strike! (Doublet STAYED UP, feedline was melted all the way
back to the house, balun and coax were fine)
>Much better to put the balun at the input of a BALANCED tuner.
I'll agree that having a balanced tuner and balanced feeders is a
superior solution.
Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr@radio.org
Quote: "Not in a thousand years will man ever fly!"
-- Wilbur Wright, 1901
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