Wednesday, April 19, 2017

The 25-Foot Untuned Vertical--7 Bands. Post #1106.

The 26-Foot Untuned Vertical--7 Bands
Author:  Dave Benzel (KD6RF)
Accessed on  20 April 2016, 02:50 hrs, UTC.
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If you want a fairly efficient, multiband HF vertical that is only 25 feet/7.62 meters long, then this untuned vertical from Dave Benzel (KD6RF) is just what you need.  According to Dave, the 25 foot/7.62 meters long antenna is "quantitatively similar" to the 43 foot/13.109 meters vertical antenna, but is only about half as long and "is designed to provide acceptably efficient operation from 40 through 10 meters."  With ground and feedline losses major issues for vertical antennas, Dave solved those issues by using 7/8" heliax feedline, an elevated counterpoise consisting of a long metal fence, and nearby "shorting rod" with a coil, which serves as a decoupling device for higher bands.

Dave provides detailed drawings, performance graphs, radiation patterns, SWR Curves, and photos to illustrate his construction and operational plans.

While this is a compromise antenna, Dave feels the project is worthwhile because most major performance and ground loss issues are solved:

A very simple system is shown here that:
• Is long enough to provide low VSWR at the low and high ends of the frequency range
• Has a “shortener” that prevents high angle lobing and radiation at 10, and to a lesser extent at 12 Meters, while not hurting efficiency at the 40 Meter low end.
• Has low feedline losses over entire 40 to 10 Meter range.
• Has reasonably near 0 dBi gain over entire 40 to 10 Meter range.
• Uses an existing metal fence line as a fairly efficient ground/counterpoise.
• Decent low angle radiation over entire 40 to 10 Meter range.
It can’t get much simpler:

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Aloha es 73 de Russ (KH6JRM)