FD40/80
Field Day 40 Meter/ 80 Meter Vertical
by WS8G
Need a quick DX antenna for Field Day or camping?
This simple antenna can be put up in 5 minutes and can be built and tuned in an
afternoon from material available in your local hardware store. Material cost
is about $15. Add another $5 and you can convert from 40 Meters to 80 meters in
one minute.
The idea is a 20 foot vertical held up by 3 guy
ropes/cords. One person can easily erect this if two tent stakes and ropes are
put in the ground before beginning to lift the antenna. Attach the cords to the
top of the antenna with an S hook and some electrical tape for a simple
attachment. Once up, the third stake is put in the ground.
The basic materials are chain link fence top rail
(1 1/8 diameter) in 10-foot sections and a piece of PVC pipe, which slides
right over the rail. A coil is built over the PVC. Your radio's coax is
terminated with two alligator clips. The center conductor is attached to the
bottom of the coil and the braid is connected to 4 radials stretched out in 4
directions on the surface of the grass around you. The antenna works well at
both 40 and 80 meters with thin gauge radials cut for 80 meters (65 feet long).
If you work only 40 meters, then cut them for 40 (33 feet long).
Details: The base section of PVC is 18 inches
long. Section B is a stock piece of fence rail measuring just over 10 feet.
Sections A and C are a second stock piece of fence railing. A is the top 18
inches of the piece with C being the remainder. If you desire to build a
loading coil for 80 meters, a third piece of rail should be bought so the top
18 inches can be used. (If you can find a bent piece in the hardware store /
lumber yard, you may get a deal on it.)
The coil is made of # 14 wire. For 40 meters you
need about 9 1/2 feet. For 80 meters, you need about 30 feet. These lengths
should give you enough extra to trim them to proper length for a great match of
about 1.5 SWR. (An alternative for switching between 40 and 80 meters is just
switching wires for the loading coil... but at 95 degrees in the hot summer
sun, with friends looking on, it is easier to swap out a section than wind the
coil. This is well worth the $5 it costs to have a separate 80-meter coil.) On
the PVC, the distance between the two screws forming the ends of the coil is 30
cm or about a foot.
SWR on 40 Meters is below 2.0 on the whole band
from 7.0 to 7.3. For 80 Meters, you can get a little more than half the band at
below 2.0. Choose CW or Voice.
The same design can be used for 15 and 20 meters
if you eliminate one 10-foot section of rail and use shorter radials. 10 meters
requires a shorter section of rail without a loading coil. But for these three
bands, another homebrew antenna is a better choice. See my 3BV20 antenna. It is
a little more complicated to build and tune, but worth the trouble.
Build this simple, inexpensive antenna - get
great S9 DX reports at 2 AM on field day - and let me know how it worked.
73s DE WS8G (Rick)