RadioBanter - View Single Post

[email protected] · July 6th 06, 09:00 AM posted to rec.radio.amateur.antenna

wrote:
Anyone ever get around the VHF FM vertical yagi feedline routing
problem by voltage feeding the bottom of the driven element with a stub
like a J-pole? A quick EZNEC run seems to indicate that it's not a bad
idea.

So it seems like it might work OK... but I wonder if anyone has
actually done it. Would you expect a coaxial stub to work better than
a parallel wire stub in terms of preserving the pattern of the yagi?

Why would you want to take a directional antenna and feed it with one
of the poorest feed systems possible?

J poles and Zepps have terrible problems with common mode feeder
current because the feedline has an UNbalanced antenna element fed by a
BALanced stub that is fed by an UNbalanced coaxial line.

If you are worried about getting the feedline down an insulated mast,
offset the yagi out 5 feet or so on a cross arm or decouple the feeder
with a self- resonant choke. You could also use a sleeve or skirt
decoupled dipole. Any of these would be at least as good as an
end-feed, and more likely and easier to make much better.

73 Tom