40m OCF Dipole
[ Version 2 ]
A Simple 4 - Band Wire Antenna.
An ultra-lightweight 4-Band wire dipole - weighs less than one pound, including 40' of coax.
Version 2 of my 40m Ultra-Light OCF dipole has been working for almost one year now.
The antenna pretty much met the goal of having a 4-band simple coax-fed dipole that does not require an antenna matchbox.
NOTE: Recalling from memory 7 years later:
I believe the feedpoint was about 43% from one end.
The SWR is under 2.6:1 on all bands, except on 10m.
On 10m it is under 2.6:1 from 28.0 to 29.5 MHz.
FIRST OF ALL, THIS IS A RESONANT ANTENNA.
If you are one of those guys who believes a random length of wire with a "Magical Magnetic Balun" is a "Wonder Antenna" . . . GO AWAY! Go read a book on antenna theory.
THE TWO GOALS OF THIS PROJECT:
- To get as many bands as possible out of 66 ft. of wire without using a matchbox. OK, it ended up being 67 ft. of wire.
- To keep the weight as low as possible so that I could get the antenna as high as possible on a lightweight fiberglass pole. HEIGHT MATTERS!
Sure other solutions have much lower SWR curves, but they only achieve 3 bands. This one works 4 bands, without a matchbox if you have a decent transceiver. (Note: I wrote this before I built Version 3, which has even better SWR).
If your transceiver folds back power at 2.5:1 SWR, maybe you bought the wrong radio. Good radios deliver 100w of power into 3:1 SWR all day long without requiring a matchbox. Worst case, turn on your rig's internal ATU.
If you worship "SWR", choose another antenna.
Unless you make it a lot heavier, you'll have fewer bands and you won't make any more contacts.
Here is a picture of the single toroid 4:1 current balun and home-brew center insulator. The legs are sloping down because the antenna will be installed in an Inverted-V configuration.
NOTE: DO NOT BUILD THIS BALUN. IT IS BASICALLY WORTHLESS!
This one is built on a piece if 3mm diameter Plexiglas.
Normally I use 4mm or 5mm diameter Plexiglas, but for this Ultra-Lightweight antenna, I wanted to keep the weight as low as possible.
Indeed, the entire antenna weighs just 335 gr (3/4 lbs.) including 40' of coax - enough to reach the ground. With this, and a 12m lightweight telescoping fiberglass pole, I can get the antenna's feedpoint up to 11m (37') in just a couple of minutes.
The ends slope to the ground in inverted Vee fashion and are simply tied off to ground stakes.
Don't worry, it is fully weather-proof. The legs of the antenna are soldered directly to the Teflon insulated wire from the Balun, and covered with heat-shrink tubing with glue inside. It is watertight.
The Toroid is a Ferroxcube TX36/23/15-4C65 and is coated with Epoxy.
A thick layer of liquid electrical tape is applied over everything.
I have never had any trouble with water leakage using this method.
NOTE my method of achieving strain-relief: simply zig-zag the wires through holes in the Plexiglas.
KEEP IT SIMPLE, STUPID!
(and as lightweight as possible)