Paul Kelley wrote:
>I finally got around to constructing my first coaxial
>collinear as per:
>
>http://www.repeater-builder.com/antenna/wa6svt.html
>
>(and using a few of Kevin's ideas)
>
>I have a question for those who have built these. Referring
>to step 9 and figure 4, I assume the decoupling sleeve
>connects a *true* (free space) quarter wave down from where
>the feedline connects to the first half wave element?
>
Correct. Plus, it *can* be longer than 1/4 wave. Many commercial
manufacturers actually use the large aluminum mounting tube at the
bottom of the antenna for the decoupling sleeve.
>Something I've discovered which may be of use to other
>antenna builders... I had trouble finding coax guts that
>would fit inside the K&S 5/16" tubing. Most of it was just
>a little too tight to be forced into the tubing. Then I
>discovered if you chill the coax guts in the freezer for
>about 30 minutes it shrinks enough to slip in! It's still
>snug but it'll go in. It then becomes *very* tight after it
>warms up, and probably cannot be easily removed. Using this
>technique, Belden 8237 and 8267 is usable for solid
>dielectric designs, 8214 for foam. Actually most 8214 can
>be forced through without being chilled. I found one NOS
>piece of 8267 that fits without being chilled, but the new
>stuff doesn't (at least not the two pieces I ordered from
>different suppliers as a test -- your results may vary,
>considering construction tolerances for both the coax and
>the brass tubing may cause unpredictable variations).
>
>Paul N1BUG
>
About 20 years ago Radio Shack sold some poorly shielded RG-8 with a
solid dielectric. This stuff works well for the dielectric and center
conductor for antenna projects, besides, the shielding was junk anyway.
Kevin
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