I have used fiberglass poles for antennas since 1972 -- here a few notes
from my experience:
1. Yes, only a few types of fiberglass poles will handle a large side load
such as the top wire of an inverted-L. Some that are sufficiently strong
include masts from The Mast Company (www.tmastco.com) and wind sock poles
from companies like Jackite (www.jackite.com), which has 28 and 31 foot
poles, as well as shorter ones. Of the easy-to-find 20-ft fishing poles,
the graphite SD-20 from South Bend is probably the strongest -- I've used
these for the top 20 feet of portable DXpedition inv-Ls with aluminum tubing
bottom sections and a #18 top wire. I have also made sturdy masts using
telescoping 1/8" wall fiberglass tubing sections from Max-Gain
(www.mgs4u.com).
2. Even the lightest poles like the MFJ 33-footer are OK for verticals if
you run the wire inside. Cut back the tip section until you expose a large
enough inside diameter to push the wire through. I've used #18 and #14 bare
copper wire and 1/8" flat braid as the conductor. The size of the wire makes
little difference if the full length of the antenna is the same size wire.
But, when the pole with inside wire is beyond a loading coil, the greater
capacitance of larger size wire or braid will reduce the required loading
coil inductance. Over the years, I've made three 2-element "short-forty"
beams using SD-20 or similar poles. The first was up 4 years in Colorado
with no problems. The current-generation model was up for 3 years in GA and
is waiting to be installed again here in WI.
3. The only "trick" I've developed is epoxying a short section of aluminum
tubing over the thick end of the fiberglass pole. This provides
reinforcement and gives you a standard-size interface to mounting hardware
or additional lengths of aluminum tubing. This and other notes were
published in QRP Quarterly -- Winter and Summer 2006 issues.
73, Gary
K9AY
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