160 Meter Top-Loaded Vertical Project

I wanted to get on the “top band”, 160 meters. Several challenges waited for me. First, the ground conductivity in Austin is about 5, to it’s difficult to get a decent ground. Second, I have only 65 feet of vertical space to work with, and this is about 1/8 wavelength on 160 meters.

Based on my experience with AM broadcast antennas, I knew the right way to do a ground system. I also knew it was not possible to do a full 120-radial ground system at my home. I decided to compromise and try to find the point of diminishing returns. I purchased enough #18 copperweld wire to build a minimum of 32 radials. I currently have 25 radials on the ground, and enough leftover wire to complete the system if the antenna doesn’t perform like it should.

I used EZNEC to design a top-loaded vertical using a wire hung from the top of the HF tower and three top-loading wires extending outward from the tower. Here’s the design as EZNEC showed it.

EZNEC showed this design would resonate higher than the amateur band.

After building the system with top-load wires significantly longer than this design, I was able to trim for resonance about 1850 Khz. The system measured 8+j6 at 1830 kHz after trimming. This was manageable.

I used a simple Pi network to match the impedance to the 50 Ohm transmission line. The vertical ended up being resonant a bit higher in Frequency than I originally wanted, so I added a small coil at the feed point to provide a bit of loading. It now resonates at 1820 kHz, and works pretty well.

I’ve worked about 30 countries with it so far, and considering I’m only running 100 Watts transmitter power, I feel like the antenna is working OK.

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Here are some photos of the 160 meter top-loaded vertical
See the entire set on Flickr