"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"

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,

Thanks for your ideas. Regarding the copper tubing issue, I was
thinking of that for two reasons.... good rigidity for the PVC to prevent
flexing, and also perhaps a better radiator. However, in raising the
question, you have prompted me to rethink that issue. Perhaps just
running some braid off of RG8 type coax in the PVC would be better in
some respects, including weight. Will keep pondering this issue.

My other problem will be to find a proper way to fasten/screw the
three elements together.

Perhaps just a PVC flat end cap on the top section with a 3/8-24 bolt
sticking up to fasten the SS whip to the top piece. As far as the other
two 7 1/2 foot sections go, I could simply do as you just suggested -
use a slightly smaller PVC piece at the middle juncture, glue it into
one of the two PVC sections, and simly pull it appart to dissassemble
those two sections. If I run braid down those two sections, I can just
leave it and fold the two PVC sections together to keep their storage
length at 7 1/2 feet long.

..... that would work. Problem is, I like the elegance of the
Shakespeare antenna, but I don't want to pay the price for one!

Ed