Topband: Feed Line

[Tom Rauch]

> have not seen it's use discussed or in print.  Is there something
> inherently wrong or difficult (besides the physical) with trying to feed a
> vertical with ladder line?  I think it would be ideal for an elevated
> radial system.

Of course we all know there are impedance transformation 
problems you might run into. A 30 ohm antenna through 1/4 wl of 
450 ohm line would be 6750 ohms at the tuner end of things. Most 
tuners are problem enough on 160, and you certainly wouldn't want 
to use anything near 1/4 wl of line to feed a 1/4 wl marconi like an 
inverted L. 

The other problem is the balanced feedline will radiate when used 
to feed an unbalanced load, like a marconi antenna. To prevent 
feedline radiation, you'd have to install a balun at the antenna as 
well as use a balanced tuner (or tuner with a balun)...so you need 
two baluns.

The radiation from the feedline can be quite problematic under 
some conditions of feedline length and grounding. With low power, 
and if the feedline is well-away from noise sources or consumer 
devices you might get away with letting it radiate, but it is probably 
not a good idea overall.

73, Tom W8JI
W8JI@contesting.com 


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