3BV20
3 Band Vertical (10, 15, 20 Meter) Antenna for $20
by WS8G
Materials are all
available at the local hardware store.
You will need Copper Water
Pipe, PVC Water Pipe, 50 ohm Coax. and 14 gauge stranded wire. Also required
are 6 sheet metal screws - Stainless steel is best. Even if you buy more than
you need of all materials, it should cost less than $20 at a local hardware
store.... The coax can be bought at Radio Shack and is cheap RG-8U.
The traps are built
with the prescribed number of turns and then tuned by snipping off coax until
the band is tuned. This process begins with the bottom trap, tuning for 10
Meters, and then proceeds to the top trap. If you have an antenna analyzer, I
would suggest beginning with the coax a little longer (by 2 inches) than stated
- then tune. If no antenna analyzer is available, the listed lengths are what I
ended up with... they should give a relatively nice match on all 3 bands.
For the traps, find a
schedule of PVC pipe which slides fairly closely over the 3/4 inch water pipe.
(I used light weight copper pipe and the low pressure 3/4 inch PVC. The PVC for
each trap is 12 " long. Drill a hole through the PVC and water pipe and
attach with a screw, which is also the connector for the wires. I drilled the
hole about a half-inch from the end of the copper pipe ends and kept a gap of
about 1 1/2 inches between the ends of the copper pipes.
Details are as follows:
Length of copper pipe:
Section A - 94 inches - Section B - 31 inches - Section C - 39 inches
15 M trap: 13 turns of
#14 wire (53"), Coax 12 inches - the center conductor is attached to the
bottom connector of the coil
10 M trap: 7 turns of
#14 wire (27"), Coax 18.5 inches
The antenna can be
divided into convenient lengths, by cutting the pipe and soldering a straight
connector to one end. the other end slides onto the lower section of pipe
allowing you to assemble it like a tent pole. I cut mine into 19 inch lengths
which can be put in a carry-on suitcase along with my rig for trips. Cut into
this many pieces, the pole bends about a foot over its length when supported by
a set of 3 guy strings. When cut into 3 pieces about 5 feet long, it fits under
the mattress of my camper and is much straighter... but neither seems to
perform better than the other.
After building the
antenna, I would suggest just a few radials for the typical field-day or
camping set-up. I used 4 33 foot radials (they also work for 40 meter antennas)
and 2 radials cut for 10 meters to improve the SWR just a bit. These radials
can be really small stranded bell wire. I got a spool of a hundred feet for a
buck a few years ago. I don't even make sure they are straight... they keep a
little bit of curl in them from where they were rolled up... but it works just
fine. If I have some time this spring I will check out the antenna with 17 foot
radials cut for 20 meters...
SWR readings are: 28.0
- 3 // 28.3 - 2 // 28.5 - 1.6 // 28.9 - 1.3 // 29.3 1.7
21.0 - 1.7 // 21.45 -
2.3 14.0 - 1.5 // 14.35 - 1.7
For the experimenter: I
also have built the same antenna with 1 1/8 inch galvanized pipe used as top
rails for chain link fence. Use the same length of wire for the coils and trim
the coax to an appropriate tuned length. The top section of pipe will also need
to be a little shorter for the larger diameter pipe... about 6 inches shorter.
Have fun building
antennas... the only art left in Ham Radio for those who have little money to
spend having fun. Let me know how this one works for you.
73s DE WS8G (Rick)