40m OCF Dipole

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.

SWR Curves:

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:

1. 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.
2. 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)