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A 28Mhz through 7 MHz Vertical Portable
Dipole
by Yukon John - KL7JR
This
design is really a spin off of my first vertical dipole,
see ( "KL7JR VERTICAL DIPOLE and Novel Matching
Method") at Hamuniverse.com for more details of this homebrew
idea.
This design does not take up much space especially for a
multi-band antenna.
40 - 10 meter vertical dipole ready
for action!
To make this antenna more portable, I used
1 1/4 inch PVC schedule 40 water pipe in 4 or 6 ft lengths for ease
of stowing inside my pick up truck and erecting. I also used #14 solid
house wire (but just about any wire #18 and larger should work) wound as a coil on 3 ft sections of the PVC pipe (one
per dipole leg) held in place by black electrical tape. Photo
below...
Coil closeup (2 required)
Approximately 18 feet of wire can be coiled
with a spacing of 1/2 inch. I left 6 inches of wire at each end for
connecting to a 102 inch steel whip and to the coax (top leg) and for the
bottom leg I just used more #14 wire pulled out at a 45 degree angle (you
could use another steel whip provided your mast is longer).
Each leg
of the vertical dipole was about 26 feet long. I mounted the PVC mast
(about 10 feet long) to the side wall of my truck. (see 1st
photo above).
I didn't have to drill any holes either. I
used the existing 1 inch diameter holes in the bed wall near the end gate
to install two toggle bolts and EMT conduit straps to hold the base of my
mast.
For the 102 inch steel whip to wire coil connection, (see
photo below),
Whip to coil
connection
I used an electrical connector,  Catalog #, T&B ADR2-B2 which is rated for
copper and aluminum both. I merely taped and ty-wrapped it to the PVC pipe
coil framework. (Editor's note: The catalog # used above
may have changed. Try the ADR2 catalog number or similar
connector)
For the coax connections I used soldered
lugs, the kind that slip inside one another for ease of antenna hook up in
cold weather.
Assorted additional pictures
below:
Center support attachment using pvc
"T" and 90 degree
"elbow"
The "workbench"
All ready for the cold Alaska
WX!
Set up was easy and fast (about 10 minutes)
on a bright sunny February Alaska morning.
I first loaded on 20 meters
and immediately KE6ZLY then KE6YNH came back to me. We traded 5x7 reports.
Next I dropped to 40 meters and my LDG Z-100 tuner quickly tuned
there, but propagation wasn't that great as I traded 5x5 reports with
another W6.
Next I QSY'd to 17, 15, 12 and 10 meters and
again the bands tuned easy but there was no propagation so I dropped back
to 20 meters to work KE6YNH again and K7CTR in Washington state. Tom and
Tim both asked about my antenna and we ragchewed for about 10 minutes then
signed. The bands just were not in all that good of shape. The guys down
south reported heavy QRM and QSB. The bands were quiet up here....too
quiet I guess.
The wind now was starting to pick up from my perch on a
pull out about 3000 feet up overlooking Anchorage .
Much to my
surprise, H44MS in the Solomon Islands called me (he was 5x9 and I was
5x6) for a short QSO. Then 20 meters took a dive so I pulled the plug on
this antenna experiment fully satisfied that the antenna worked out. This
was the first time I used long coils such as these for an antenna. In the
future I will use them again I'm sure.
Further experimenting on
the wire length and mast height (and perhaps a more rigid mast for a
permanent installation) should yield you better results. Good luck and
have fun experimenting with antennas!
73, de Yukon
John
KL7JR
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