Ham Radio Help Desk

As my local club in northern Virginia prepares for the March Virginia QSO Party many questions are asked about how best to take full advantage of Near Vertical Incident Skywave (NVIS) communications so critical to maximizing contacts on HF within the state.

In particular one member has a magnificent full wave 160 meter loop up around 50 feet or so. He is contemplating using it for NVIS on 80 meters. He desires to lower it to about 15 feet to improve the NVIS characteristics.

It is true lowering a dipole will focus more energy straight up while reducing the energy towards the horizon. This is a tried and true technique on 80 and sometimes 40 meter NVIS and offers a potential added benefit of less sensitivity to far away thunderstorm noise. This is a method of diminishing returns; Lowering the antenna favors the sky more, but the overall gain is reduced. In other words, less signal is focused in a better NVIS favoring pattern.

Full wave loops are quite different as this EZNEC simulation suggests. Here is a simple four sided loop with 128 foot sides and fed near one corner – just like my friend’s 160 meter loop.
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During the past several Virginia QSO Parties, members in our club have experimented with several antenna solutions.

Some have the big bad beam high in the sky with an 80 meter dipole added.

Others have smaller beams and more wire antennas.

Others go mobile on VHF and HF.

Still others go expedition and construct antennas that lend themselves towards portability.

I am considering added a 75 meter turnstile antenna to my station.
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