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80m Loaded Dipole

This Antenna came about the need for an 80 m antenna to supplement a SteppIR Antenna at a local Amateur Operator. The previous 80 m antenna was detuning the SteppIR and so one of the requirements is to have no resonance at any other frequency.

Well, I got close., there is a resonance at 53 MHz, but this is not a big issue. So the requirements are:

- - - - Fit into the yard, max 31 m span.
        No resonance on any other HF band.
        Usable at the low end of 80 m (Digital modes and Voice) 3.575/3.6 MHz.
        Good efficiency.

Pic: 1

Pic 1 shows the output of a small program I wrote many moons ago and then ported to run on a PC architecture, to get into the ball park for the antenna dimensions. So using those values in 4Nec2 and a little tuning we end up with the below details, Pic 2.

https://sites.google.com/site/vkonehw/home/antennas/80m-loaded-dipole/80m%20loaded%20dipole%2031m%203575%20data.PNG

Pic: 2

Quick check to see if there is any hint of resonance, Pic 3.

https://sites.google.com/site/vkonehw/home/antennas/80m-loaded-dipole/80m%20loaded%20dipole%207-53MHz%20swr.PNG

Pic: 3Checking for resonances across 30 MHz

Pic: 4Good VSWR across the required Frequency Spectrum

Lets have a quick look at the current distribution, Pic 5.

https://sites.google.com/site/vkonehw/home/antennas/80m-loaded-dipole/80m%20loaded%20dipole%20current%20magnitude.PNG

Pic: 5

At Pic 5 we can see that the loading coils are still in a high current zone, can't be helped if the antenna is not to be resonant on any other HF band. We will however lose efficiency because of that. How much, well lets have a look.

https://sites.google.com/site/vkonehw/home/antennas/80m-loaded-dipole/compare%2080m%20vs%20loaded%2080m%20tgain%20hplane.PNG

Pic: 6Red = Loaded 80 m DipoleBlue = Fullsize 80m Dipole

https://sites.google.com/site/vkonehw/home/antennas/80m-loaded-dipole/compare%2080m%20vs%20loaded%2080m%20tgain%20vplane.PNG

Pic: 7Red = Loaded 80 m DipoleBlue = Fullsize 80 m Dipole

As we can see at Pic 6 and Pic 7 there is a little bit of loss, not even 1 dB (0.89 dB). This antenna, at 7 m height will be a cloud burner (NVIS), however it has good 3:1 SWR bandwidth, should not be interacting with other antennas in your back yard and will get you on air on 80 m. Trimming the ends will be necessary regardless where you build this antenna. But make sure to use a 1:1 current/choke Balun for best performance.

NOTE: Most will install the antenna in an inverted V configuration and this might give the impression of improve performance.

However I would recommend not to make the apex smaller then 120° in an inverted V installation.

Here are a few Photos from a build by a mate of mine .... Very nice build but also quite heavy ....

80m loaded dipole

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