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Old October 2nd 05, 06:26 PM
Dave VanHorn
 
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With the tubing over a coaxial cable though it seems there is Vp related
to the dielectric formed between the sleeve and the outer sheath of the
coax cable but also the Metal has an Er value.


From what I understand, the RF will be traveling on the outside of the
sleeve, and won't "see" the internals at all.
So, the sleeve ends up as a 1/4 wavelength stub.

Is the diameter of the tubing critical (will it impact adversely
on SWR looking into this antenna).


It shouldn't be

The final point would be if I place some ferrite rings across the coax
below the sleeve, will this improve SWR ?


Not if the sleeve is doing it's job.
The sleeve's open end should look like a short at the operating frequency,
and keep RF off the feedline.


Thanks

Regards

David

David;

That's why they call it the ART of antenna design. First you make the
best mathematical calculations you can then you start cutting wire/tubing.
Make your lengths slightly longer than the math says then prune the
lengths until the antenna works the way you think it should.

There are so many variables in antennas that this is the only practical
way to make a new one. Once you find your optimal lengths you can make
more to the same specs. However remember that just like in housing
antenna's depend on three things: location, location, location and have to
be custom adjusted for each site.

Dave WD9BDZ