Over the past weekend I built a single wire beverage in my back woods. The antenna is 480 feet in length, it runs 5 degrees northeast and the average height above ground is 10 feet. I used RW90 stranded 12 AWG wire for the antenna and it is supported on Red Snap'R electric fence insulators. I used an ICE 180A as the isolation or matching unit at the near end and the ICE 185A at the far end for impedance matching and termination.
Based on information supplied by ICE, I had initially set the taps in both ICE beverage boxes (near and far end) for 600 ohms. They suggested if the beverage was between 8 and 15 feet above ground the 600 ohm tap should provide the best overall SWR match for the antenna. This was a starting point, but as you will see in the SWR sweeps below, the optimum value was lower.
The W8JI website suggests the objective in fine tuning a beverage is to sweep the antenna at the feed point from 1.8 to 7 MHz (or over a ~4:1 frequency range near the frequency intended for antenna) while watching the SWR -- and adjust the (tap) termination for minimum SWR variation -- not minimum SWR. At 600 ohms the SWR variation was significant, but at 450 and 300 ohms respectively, the variation far less. The 450 ohm and 300 ohm sweeps are shown below. The blue dotted line is my SWR reference point so I could see the variations from the line. These readings are taken using a WX0B (AIM 4170) antenna analyzer.
450 ohm tap in the ICE boxes -- measured at the near-end feed point
300 ohm tap in the ICE boxes -- measured at the near-end feed point
This is a screen clip of the fed-point SWR curves for 450 and 300 ohm taps:
450
ohm SWR values
300 ohm SWR values
The near end termination box layout
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Last modified
December 01, 2007
Copyright © 2000 -2007 Paul B. Peters, VE7BZ. All rights reserved.
