Extended Double Zepp
A simple high gain doublet of sorts
I was recently asked about a high gain antenna that could be built with just some wire and rope and the extended double zepp came to mind So I descided to take a moment to model and share the results. For the uninitiated, the extended double zepp is nothing more than a doublet with 5/8 wave elements rather than 1/4 wave elements on the design frequency.
I designed this antenna for 80m at 1/2 wavelength above earth but since this antenna is basically just an oversized doublet, it will also cover 160m as well as the upper HF bands. It's fed with window line and requires a wide range antenna tuner with either a balanced output or a unbalanced output with a short run of coax into a 4 :1 balun to match to the window line. Here are the results:
80m Performance
A view of the antenna with each leg showing the typical current distribution of a 5/8 wave antenna, but in anti-phase to each other. The legs are 157' each and total length is 314'
The azimuth pattern shows 10.81 dBi gain broadside to the antenna with a 36 degree beam width. The gain of this antenna compared to a horizontal resonant dipole at the same height is roughly 3.5dBi.
The elevation plot shows this antenna has a typical radiation pattern for a dipole at 1/2 wavelength above ground.
Performance On The Other Bands...
On 160m-80m, peak gain is broadside to the antenna
On 40m and above, peak gain is achieve just off the ends of the antenna on multiple lobes
160m
40m
20m
10m
