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Modeling the Double L Antenna on a 70 ft Tower
I had stumbled upon K2KQ's interesting Double L design on the YCCC website. It seemed to be a likely candidate for my application as it had several benefits:
Easy/cheap to construct
Forgiving in terms of tuning
Easy to feed (no matching network required)
My next step was to model the Double L in MMANA. My model of the Double L included a tower and a yagi as used in other models. The K2KQ design calls for two dipoles bent into a C shape and connected at about the midpoint of the tower (mounted about 3 ft away). The 160 meter dipole is 270 ft. and the 80 meter dipole is 130 ft. In my model, I had to account for sloping elements due to a lack of surrounding trees/supports. Here is the model of the Double L as it would appear on my 70 ft ANWireless self-supporting tower.
SWR & Bandwidth
The bandwidth on 80 meters looks to be excellent for the Double L. It's easily useable across the entire band with little effort. If an adjustment was necessary, it would be easy to tune by changing the length of the lower element.
The 160 meter SWR plot of the Double L is shown below. I was unable to tweak the antenna to a perfect match. However, the 58 Hz below 2.0:1 is not too shabby.
Far Field Plots
The far field plot for the Double L 80 meters shows a lot of energy lost to high angles. I suppose this antenna is simply looking more like a dipole than an Inverted L on 80 on my tower.
The 160 meter plot shows a decent pattern.
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