My 10 Meter Band Extended Double Zepp antenna – K3URT

 

I was looking for more directionality on the 10 meter band, so I created an Extended Double Zepp (EDZ) antenna The object of this antenna: purportedly the 3 db gain, more directional, and to bypass a tuner.

 

Let’s start with the calculations for making an EDZ. Beware folks! The Internet is full of speculation from some seemingly reputable folks. I can only let you know about my experience with lots of perspiration and pruning.

 

The ARRL Handbook for Radio Communications, 2014, (p. 21.22, 91st Ed., Newington, CT) is the basis for my calculations. The EDZ is actually two Zepp antennas put together like a dipole in collinear fashion, but implementing an electrical .64 wavelength per side (I used .643). Using the formula 643/frequency in MHz=length in feet for one side. I choose the frequency of 28.25 MHz largely because I work digital modes below 28.3 MHz, but occasionally voice above that.* Therefore, one side of the element (L1 and L2) is 22 feet and 9.13 inches (I rounded down to 22 feet, 9 inches). Total length then is 45 feet and 6 inches long (L1+L2).

 

For the transmission line I used 450 Ohm window line cut length of 4 feet attached at the center at one end and the other end attached to a 1:1 current balun - 52 Ohm coax attached from the balun to the radio. Only use a 4:1 balun if NOT using coax! By the way – I did not close “short” the window line at the end!

 

The 4 feet 450 Ohm window transmission line (sometimes called “ladder line”) was determined by using 1/8 wavelength less 10% (1005 full wavelength X .90 = 904.5/8=113/28.25 Mhz = 4 feet.)


Does the coax length matter? Yes, the longer it is, the less in gain. I have about 29 feet coax total. It is also important that the 4 feet window line drop down vertically. When pulled nearly horizontal with the antenna my antenna analyzer didn’t like it. The center impedance of the antenna is approximately 140 Ohms according to
the ARRL (my Smith Chart was indicating 160 Ohms), which is why when I used a 4:1 balun the SWR was always high and didn’t match on any frequency (the radio was reading 30-40 Ohms to its match of 50 Ohms).

 

How does it match up against my 80 meter Doublet? For directionality, the EDZ does work better than the Doublet on 10 meters and in directional gain the EDZ has a slight edge. The EDZ, which works broadside to a signal, is broadside oriented the two major lobes 60º/240º - hitting central Europe and the Middle East and Central America. The two minor lobes are 140º/320º - down the Atlantic Ocean and the Pacific Northwest; and 180º/360º - hitting eastern South America and directly north of me encompassing Canada over the Pole and into central Russia.


I worked a Scottish and an English station very easily with 100% copy - directional to them (PSK31 mode using 30 watts). I also worked an Uruguay station, a Brazilian station and a Cuban station. The difference was noticeable! When using the new EDZ compared to the doublet, the signal was almost down in strength for the south Americans, (of course, it is not directed to Brazil and Uruguay). Cuba was the exception. A Colorado station (minor lobe his way) was very directional.


So, the directivity is definitely there!


Overall I am happy! 73 de K3URT


* SWR was 1:1 to 1:4 from 28 to 28.5 MHz.


Image is not to scale.