"Ed" wrote in message
. 192.196...


I wish to build a 23 foot whip antenna similar to the Shakespeare 393
HF
marine antenna, ( quite pricey ). It must be in three 7 1/2 foot long
sections and screws together, as shown he http://shakespeare-
marine.com/antennas.asp?antenna=393

I'm thinking along the lines of a 7 1/2 foot stainless steel whip on
top of two 7 1/2 foot long segments of my own construction. At present,
I think the two bottom sections would be copper tubing, enclosed within
PVC pipe. Although I have some ideas for the connections, I would like
to hear from others their ideas on both the building of two stiffer bottom
sections for this whip, along with ways of fabricating the screw-together
connections that would be both electrically sound and sturdy. The whip
will be for fixed mobile operation at a motorhome. The entire assembly
must break down and fit within a larger 8 foot long PVC tube for storage.

Ed, I have been thinking of a self-supporting whip, too and I am also going
to try big PVC, which is pretty rigid per unit length. I think adjacent
sizes would fit smaller-into-larger with two or four slots several inches
long cut into the larger pipe. Your application might use two sections of,
say, 1 1/2-inch PVC pipe, each 7 1/2 feet long and a shorter coupling piece
of 1 1/4-inch PVC pipe where they butt together. The large pieces would
have linear slots cut into them, with hose clamps on each side of the
coupling. (Lest anyone think I was neglecting pipe couplings that are made
for PVC -- no -- I just don't think they'd be very strong.)

This is all theoretical, mind you, as I have yet to put any pipe together,
myself. I have already thought of several variants, including: (a) using
a coupling piece larger than the two 7 1/2 foot sections, rather than
smaller and (b) making the lower 7 1/2 foot section larger than the upper
one, slotting just the lower one and thus omitting the coupling piece.

PVC has the advantage of having numerous adapter/reducer combinations to get
you to a suitable fitting for the base of your intended stainless steel whip
top section.

Question: What would you gain with copper tubing inside your lower PVC
sections. Slight BW increase, perhaps? It seems to me that it creates an
attachment problem, compared to just dropping a single conductor down from
the stainless steel whip, through the center of the PVC and out to the tuner
attachment. Speaking of that, including a PVC T-connector in the lower
section, perhaps a few feet off the ground, would give you an exit point for
the radiating element, but it would probably louse up the process of storing
the whole thing inside your 8 foot PVC tube (whose diameter is not given).

"Sal"