.64 Wave 20M Dipole

[N3ATS]

I designed another antenna. In internet searches some call this a "Half Extended Double Zepp", although there is not much written about .64 wave center fed dipoles.

It's fed with a pre-determined length of 300 ohm ladder-line which provides a matching section. At the end of that, a 1:1 balun is installed and then you can use 50 ohm coax right to your transceiver. This is a single band antenna. Though it could be tuned for other bands, the loss from the coax would prohibit that.

The antenna offers as much as 7.66 dBi Gain at a 30 degree takeoff angle. The test model is hung at 35' AGL, and is approximately 43' long overall. The matching section of 300 ohm ladder line is 82' long. From there an LDG 1:1 balun is used followed by 18' of RG-8X to my rig. The antenna is constructed of 14 AWG copper wire and EZNEC shows it produces 5.5 dB gain over a dipole.

Does it work? Yes! Damn well! I have been using this antenna for PSK31 at 50 watts for the past 4 months. Here is a link to my logs...
http://n3ats.com/?Online_QSO_Log::HF_Log

Enjoy!

http://n3ats.com/images/Antenna_Drawing.png

http://n3ats.com/images/Elevation_Plot.png

http://n3ats.com/images/Azimuth_Plot.png

http://n3ats.com/images/SWR_Plot.png

[w2amr]

Cool stuff .

So is this thing 82 feet off the ground? The doublet portion?

I am interested to know how closely the SWR matches up to the EZNEC values.

Looks like you did well.

[N3ATS]

No, the doublet is 35' off the ground. The ladder-line portion is 82' feet in length. It is very, very close as far as SWR goes. I have one hanging in my backyard right now.

So what do you do with the remainder of the <50 feet of ladderline?

[N3ATS]

Run it to your shack. This specific length tunes the antenna.

[N3ATS]

I just got a new laptop so not all of my files are on it. When I start moving stuff over I will post the EZNEC file for you.

All the ladder line does is tune the antenna. It brings the resonance into the 20m band. The advantage of the longer wire is a larger capture area and a bit of increased gain over a standard dipole.

I am no antenna expert by any means, but I can attest to this antenna working, and well.

Everyone one of http://n3ats.com/?Online_QSO_Log::HF_Log those QSOs were done with this antenna.