A Portable 75/40* Meter NVIS Antenna

by David B. Murray, KD1BL

Background:

While taking the Level II Emergency Communications Course, my mentor, Ron Kane (AD6KV) presented information on Near Vertical Incidence Skywave (NVIS) operation. Being interested in the reputed “no holes” coverage in mountainous regions, I used the Google Search Engine to learn more about NVIS antennas. With the wealth of information about NVIS operation available on Google, this artical will focus on construction and effectiveness of my “cloud warmer”.

Bill, W1WAW, and I decided to set up NVIS antennas at our respective locations in northwest Vermont, and to use them to communicate on a daily basis over the two major ridges between us. I also have a CW-160 antenna averaging 40 feet high, so that antenna provided a comparative benchmark. We have held 8AM QSOs daily for about 4 months. Recently Earl, K1YLB, joined us each morning using his NVIS dipole which slopes from 10 to 20 feet above ground. Bill’s NVIS dipole is constructed much as presented below, and is 10 feet above ground. Mine is hung at 8 to 10 feet above ground between two trees.

What we have learned has been very positive! Thus this article.

Range:

The 80 meter NVIS antenna consistently provides dependable communications from the northwest corner of Vermont to over a 350 – 400 mile RADIUS range, covering all of New England, down into Pennsylvania, and westward to the Niagra Falls area. I have been able to communicate reliably with any station in that area without asking for fills. The message gets through! My 40 meter NVIS work has been more limited, but I expect to have developed more information by the spring of 2008. The NVIS antenna should be a strong candidate for emergency communications in mountainous terrain!

* This article accurately shows the layout of the 75/40 meter antenna. All the performance information in this article relates only to use of the 75 meter portion. My experience has shown that 40 meter NVIS activity has been possible only since early November. Using the NVIS F2 Layer Status Map one can learn toknow when 40 meter NVIS work is possible. That map is updated at about 42 minutes after the hour. During the late Fall to early Spring, I expect to see daily 40 meter NVIS work available.

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