160 Meters Using Tower As Vertical Antenna

An omega-matching system was added to the tower when it was on the ground in the hopes the tower could be made into a 160 meter vertical antenna. The concept was suggested by Bill, N0CU and illustrated in ON4UN’s Low Band-DXing, Fifth Edition on p 9-68.

PVC pipes were attached to the tower with stainless steel clamps and 8 ga aluminum wire was connected at the top.

Today was the first chance to see if could be tuned. Two large variable capacitors were mounted temporarily, one in parallel with the tower and the other in series with the feedline. It is held up by Velcro strips and connected with clip-leads.

The results were amazing with the capacitors set at half way on the first try. This is what it looks like on the RigExpert AA-55 antenna analyzer.

With a little tweaking the match could probably be made perfect. It is quite useable right now with no other adjustment. Upon re-reading some of the technical articles on gamma matching a tower some new (or missed) information came to light. The main point is the resistance of the match is determined solely by the gamma apparatus connection height and distance from the tower. Resistance cannot be changed by the matching unit. If this proves out we are stuck with 66.5 ohms.

Next the clip-leads were carefully removed without touching the capacitor settings. A Banggood tester was connected to the capacitors and readings were taken to determine a ballpark figure for required capacitance.

The Banggood shows one capacitor is 82pF and the other is 116pF. Capacitors to achieve these values but with higher voltage ratings will be obtained. Next step is to mount them more permanently in a NEMA box and attach the box to the tower. Getting ready for winter and the fabulous upcoming 160 meter DX season will be fun this year.

A new box with two variable capacitors is ready to be installed and adjusted. The capacitors are capable of handling a peak voltage of 3KV. That should be right on the edge of being ok.

Update 9/6/2020: New box with room for two 3KV variable capacitors has been installed and tuned up.

The results are below 2:1 swr but not down to 1:1 which was the goal, of course. Moving the gamma tap point location would probably be necessary but too much work to accomplish. One article mentioned moving the gamma wire closer or farther from the tower down at the matching unit level. That will be given a try later this month. Here is an analyzer view of the match. This was taken at the shack end of the coax.

The SWR of 1.27 is lower than we measured at the base of the tower due to the coax loss. At the tower the swr was slightly higher at 1.45 and the resistance was up to 72 ohms.

Next update will show some on-the-air results.

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