Doublet with 160 meters

My new QTH (c. 2018) featured a long list of honey-do’s, pushing a real tower project back at least a few years. The good news was that it also featured very high pine trees; one particular specimen is at least 150′. I decided to take advantage of the high pine trees while daydreaming of aluminum.

The antenna is a typical doublet cut for 80 meters, about 130 feet long in total, and fed with open wire line directly to an MFJ-998rt autotuner at its base. The use of open wire line avoids the high loss characteristic of coaxial feedline at high SWR. The antenna supports are a 150′ pine at the south end and a 100′ pine at the north end, both placed by an arborist.

Although this antenna is higher than the average doublet, it still isn’t high enough to be competitive on 160 meters. For this, I knew that I needed a vertical. This can, of course, be done with some tricky switching: the open wire feedline is shorted together to form a Marconi-T against a radial field. It was a convenient surprise that the open wire feedline is about 120′ long, almost exactly 1/4-wave at 1.8 MHz!

Like most verticals, this antenna is only as good as the radial field beneath it, so I unrolled almost two acres of galvanized hardware screen during a yard remodel. I chose to use screen as opposed to radials due to the strange shape of the yard, although I have experimented with radials above the screen, both bonded and floating with little effect.

The antenna works well, probably because of its height. Band changes are a breeze, as a single dit on the paddle is often enough to trigger the autotuner memory. The relay box changing from doublet to Marconi-T at the base is operated by the radio band decoders, eliminating any manual switching by the operator.

After several months of using this setup and extensive testing with the Reverse Beacon Network, it looked like the antenna wasn’t great on 20 meters — and indeed I felt weak on 20 in contests. Instead of fiddling with the antenna any further, I hung a 20 meter delta loop near the top of the tall pine and it works significantly better for that band. It is positioned in such a way that there is no interaction with the doublet.

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