New 10 Meter Dipole

About a month ago I started working on an End-fed half wave dipole for 10 meters. The results were quite unsatisfactory (for reasons yet to be explored) so I decided to go a slightly different route. Some research and a look at the book More Wire Antenna Classics led me to begin exploring the Double Extended Zepp antenna.

Smith Chart for 10 Meter Dipole Matching SectionI started out by measuring out 251 inches of wire for one leg of the antenna. Then as I was measuring out the other leg my spool of wire came to its end. I was now left wondering if I was going to be able to build the antenna I wanted as I was looking to build something that would work mostly in the Novice subband of 10 meters as that tends to be where most of the activity is. So I created a quick model of a dipole with 248 inch legs and was left with a reasonable result. The SWR was a bit on the high side with an impedance of 293.8-j1000 ohms at 28.4 MHz.

10meter_de-zepp_gain_swr.pngI plugged this load value into my Smith Chart program (LinSmith) and added a series 450 ohm transmission line. Much to my surprise, 180 cm (roughly 70 inches) of line would bring the impedance down to 46.5+j1.2. I updated the antenna model with a 70 inch transmission line and while the low SWR point was much higher in the band than I hoped I was happy to try it to see what happened in real life. Thus I began assembling the antenna.

10meter_de-zepp_radiation_3d.pngI put the antenna up in my front yard with the center in one tree, one end in another tree on the other side of my driveway and the opposite end tied to a flagpole. The height is around 12 feet and SWR around 28.4 MHz is surprisingly lower than predicted by the model (around 1.5:1).

Time will tell how well this antenna works as I was too preoccupied to attempt to work anyone during the nice opening on 10 meters today. However I did hear a W7 and several VEs working an EC8 this afternoon which was quite encouraging.

Update 24-Oct-2012: Today I worked Les, VP9/N1SV, in Hamilton, Bermuda and received a 59 report using this antenna and 100 watts on my IC-706.

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