NVIS Antennas

Understanding Amateur Radio NVIS Antennas and Propagation

Copyright © 2002-2011 by Harold Melton, KV5R. All Rights Reserved. Feel Free to Link to This Page.

NVIS Antennas: Page 1

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Background

The author, a professional technical writer and training developer, has written adult vocational training materials for the petroleum refining, chemical, and aviation industries; and various technical articles for amateur radio. He has also been studying, building, and testing antennas for about 30 years as a hobby.

The material in this article is derived from The ARRL Antenna Book, 1957, 1974, and 1999 editions; Army Field Manual 24-18 and others, several QST articles, and various web articles written by other NVIS experimenters and HF antenna and propagation experts such as W4RNL. Various specifications given as examples are rough estimates, some with wide variability. They do not represent the absolute limits of performance, but practical applications where a high percentage of messages may be passed accurately, under average conditions.

This article is not intended to be a complete primer on HF radio propagation or emergency communications. Users needing background in HF radio propagation should see several of the excellent links at www.eham.net/DX/propagation, the many links at the bottom of this article, and the ARRL Antenna Book. The author assumes that the audience for this article has a general understanding of HF antennas and ionospheric propagation. Users needing background in emergency communications should see the various web sites of ARES and RACES groups, as well as FEMA and MARS sites.

The author wishes to thank all that have contributed useful information on this subject, and encourages comments, in writing, that may be used to improve this article. To quote a great writer from the 1830s, “Before you can convince me of error, you must first convince me you understand what I say.” Please read carefully.

Continued…

14 thoughts on “NVIS Antennas
  1. In region 5 of Army MARS we regularly use NVIS. It does help to have frequencies available in the 2,3,4,5,6,7 Meg range under the current solar conditions.
    Art, N9AOP

  2. I have been using an 8o meter NVIS horizontal full wave loop for several years now and it is a very good low noise antenna on receive and a mediocker transmit antenna. It has a low signal-to-noise ratio ! I mostly trasmit on a dipole array and receive on the loop. Some bands I use only the loop for transmit/ receive. I feed the loop with a 1 to 4 balun on 80 meters and in series with the balun, an electrical 1/4 wave of 75 ohm RG-6 coax to match it on 40 meters. Check the impedence of your loop to determine how to feed it. Willy K3VW

  3. I’ve also worked stations on 30m during daylight hours (Noon +/- 2 hours) from 20 to a few hundred miles via NVIS propagation. Although 30m NVIS mode is less available than 40m or 80m, when it’s open signals are quite strong with very little QSB.

  4. I ran into NVIS antenna operation by accident. I use a 90 ft. clothes line , about 12 ft. off the ground. I couple that to a 35 ft. long single #12 copper wire I found. So now its a low slung dipole. . I use a YAESU FT.-817 radio with a Z-817 tuner. . .My average distance is more that 300 KM and its not unusual to reach nearly 1000 km. Last week, My QTH was Mid Vancouver island BC, and I had a good QSO with a party in Cocolalla Idaho!!

  5. I like NVIS for short haul stuff on 40 and 80m. I have had good experience with a horizontal loop about 30 ft above ground. I fed it with 450 ohm ladder line and an SGC230 tuner. Very reliable for emergency communications type work. I would have put the loop lower but stuff was in the way. You just do what you can. Not sure what the guy was harranging about who said they just don’t work. Maybe he was attempting DX. In NVIS 40 and 80 seem to be the only two bands worth working. No shallow angle transmission for long distance. The signal goes up and reflects back down like an umbrella. If the ionosphere does not cooperate then you are out of luck.

    • I should mention I’m in the process of assembling another full wave 80m loop antenna. The first one got damaged in a horrible storm. I’ve tried other antennas for NVIS and nothing seems to work as well.

  6. I have read several articles on NVIS and spent time in the Military who also use NVIS for Tactical command and control situations… Believe me, if it did NOT work as it is touted to, the Military would NOT waste their time with it… That is the reason most of the Military Vehicles you see have their mobile antennas bent over and tied down… To take advantage of the NVIS method of sending signals… On 40 meters I have no desire to send signals to Europe, Mexico, South America or any other DX so an NVIS would suit my purpose perfectly… I’ll know how it works within the next couple weeks…. Thanks… WV8RS…

    • Unfortunately he didn’t say… But generally speaking, a reflector is a linear conductor that is ~5% longer than your half-wave dipole, spaced ~.2-.25 wave behind. It also needs to be >8 feet high to (a) decouple it from earth and (b) keep it out hair/mower/tractor/wife/dog, etc, thus, if your dipole is <~60 feet high don't mess with a reflector under it.

  7. well been using a 10ft high 40mtr NVIS for abt 3 mo. I have 10ft wide ‘reflector’ under ant. BOY! it makes me look like am running a kw or more(rig is kenw 520, 100 wts). I get called a lier by some of those old timers when I tell them abt the ant. my 100wts is as strong to them as I see them. hi hi. it’s the ONLY 40 mtr ant I have………….WB5HDS

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