[Antennas] Re: increased ant bandwidths...

[Danny Richardson]

At 11:41 AM 4/30/2006, you wrote:

>...precisely guys. And that's the reason that-especially when using an
>antenna tuner- it's better to use an open wire feeder. The expected loss
>from such a feeder is about one tenth of the loss from a coax feeder. There
>is a nomograph  in Walt Maxwell's "reflections on reflections " book that
>shows it.
>Sooo, as long as you use a tuner go for the Rolls Royce: open wire or as
>close as you can get. I've seen those in radio stations at power levels of
>tens of kW and they worked without a hitch.

There are many factors to consider when choosing an antenna system and feed 
line loss is just but one of them. I have never found one antenna system 
ideal for every situation. For example; why would I want to go to the 
trouble of using tuned feeders with a typical mono-band beam installation? 
Is the difference in transmission line loss worth all the extra effort? 
Would a receiving station be able to hear it?


>BTW, wide spacing is not needed, nor wanted: the closer the spacing, the
>lower the residual radiation from the line( small in any case, being
>balanced.

Not true. The closer the spacing the lower the characteristic impedance - 
the lower the characteristic impedance the higher the loss. 600-ohm line 
has a lower loss than say 300-ohm line - especially when wet. Same is true 
for the popular 450-ohm line.

Check out Wes Stewart, N7WS's paper on the subject. 
http://k6mhe.com/n7ws/Ladder_Line.pdf

BTW: I use open line feed doublet here, but also have other coax fed 
antenna systems - depends upon the application.

73,
Danny, K6MHE 


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