What do I call my antenna?

The main HF (High Frequency) antenna for use on the amateur radio bands is a "doublet dipole." It is one of the top five all-round favorites of the late L. B. Cebik, W4RNL, sk.

The antenna was home brewed by me, but the basic design and concept is as old as radio: the dipole. The classic dipole is a half-wave length divided by the lowest frequency designed for use (468 divided by frequency in Megahertz = length in feet). The dipole is popular because of its simplicity. After World War II 50 ohm coaxial cable was plentiful and manufacturers were making radios at 50 ohm impedance at the input. Half-wave dipoles (two quarter waves connected in the middle with the fed line) are 50-72 ohm by design, hence a close match with the coax and modern radio impedance.

So, if I fed my 142 foot long wire antenna (two, 71' halfs) with 50 ohm coax cable it would be called an unbalance 80 meter dipole, resonating below the 80 meter band (about 3.3 MHz per analyzer). It is 28.6 feet (8.73 meters) high at the center apex, sloping down to 23 feet (7 meters) at the ends – a very mild inverted V.

The antenna is fed with 450 ohm window line instead of coax, making it a balanced non-resonate antenna. Some call is a classic doublet antenna, tuned with a tuner with a 4:1 balun to make it match the radio at 50 ohms input.

It can also be called a Extended Double Zeppelin (EDZ) antenna. An EDZ  length is calculated at 1256* divided by frequency = total length. This makes my antenna essentially a EDZ antenna on amateur 30 thru 10 meters (10.1 to 29.7 MHz) bands. But this antenna is not a true EDZ because it is for multi-band use. EDZ antennas are resonate on one band and are coax fed.

I used a G5RV, Jr. antenna for 10 to 40 meters in the past. The G5RV Jr. was 51 feet long fed in the middle with window line extending down vertically for 17 feet then fed by 50 ohm coax which went underground and into the radio room. With the home brewed current balun, the total was 100 feet of cable. As a result, my signal loss was significant.

The doublet has practically no loss despite the length of the feeder. When I erected the doublet antenna with 51 feet of window line coming into the radio room, I notice substantial gain! I was finally being heard on the bands and not struggling to be heard (in voice mode I run about 95 watts, on digital modes around 30-45 watts).

So, I now have a non-resonant balanced fed antenna. For simplicity and brevity, I call it a 43 meter long Doublet for the 80 thru 10 meter bands. It works on the 6 meter band, but as you go higher in frequency with antenna of this length, the impedance goes higher causing some problems with tuning (however, I have never had that problem).

Physical Description: the wire is 18 gauge copper stranded, 71 feet per side of the antenna (142 feet total), fed by 450 ohm window line into a 4:1 balun tuner (built-into the MFJ-949E) then about 18" of coax from the tuner to the “rig”.

73 de Curt, K3URT

REVISED: 9 February 2017

* I have seen variations of this formula from 1197 to 1286. An EDZ is generally two 5/8 wave elements or 1.25 wavelength total length long.

© Curt Sanders 2017, all rights reserved.