Near Vertical Incident Skywave (NVIS) Antennas
During my years in the military I was surrounded by communications equipment and great men and women that operated the gear. One thing I learned very quickly as a Private First Class when I was going through communications school at the 13 Area (Main side) facilities at Camp Pendleton, California was that 95% of the battle with communications was a good antenna. Over the years this has been proven time and time again. Having a good antenna that is resonant makes all the difference in the world. It can also mean the difference between saving your life or not.
The antenna being discussed in this article is a bit controversial in that some believe that it has very defined capabilities on just certain frequencies while others feel that it has greater capabilities than generally described. What I know is that I have used Near Vertical Incident Skywave (NVIS) antennas in the military and as a ham operator under very different situations with good results. That’s all that matters to me.
As an amateur radio operator (ham) I have developed my own version of the NVIS antenna and have found it to work remarkably well in different modes and on different bands. Over the last couple of years I have used it for the numerous digital modes available on the ham bands and have found it to work very well. I have been able to make contacts in Canada, Mexico, throughout the United States, and even had a screen shot emailed to me from an operator in Japan while using a digital mode called Olivia. He had a 100% copy on me. Amazing! Some would say that was impossible but it happened. Suffice it to say, the antenna was not designed for long distance communications. It was designed for operators to communicate over mountains, islands, buildings in large cities, and over short (500 – 1000 miles) distances.
The NVIS antenna comes in several different varieties; loops, end-fed long wires, mobile verticals that are bent over, a few types of dipoles, and the other designs. The design I developed was a version of one I saw years ago. By adding a couple of “tweaks” here and there I was able to end up with a really good antenna. Mine is a modification of the one shown in Figure 1 below.
This particular antenna design seems to work well as it has a very high takeoff angle which is critical for any NVIS antenna.
Figure 2: Example of an Elevation Pattern of a 75-Meter Dipole NVIS Antenna
The whole concept of the NVIS antenna is to have the signal going almost straight up (thus the Near Vertical terminology) and hitting the ionosphere reflecting back to the ground like the “ribs” of an umbrella. (Figure 2) Three factors must be kept in mind when utilizing NVIS antennas and they are POWER LEVEL, ANTENNA HEIGHT ABOVE GROUND LEVEL, and the FREQUENCY being used.
When communicating over mountains, such as the ones I have in my area of the country, this can be accomplished with very little power. In fact, I communicate daily on National Traffic Nets (NTS) and with other hams in the Rocky Mountain Region using 10 watts or less. Most of the time I use 5-10 watts of power to communicate on the digital modes and up to 20 watts or a bit more on phone (SSB voice) depending on the band conditions. Again, having a great antenna is 95% of the battle in good communications in amateur radio.
One thing that is critically important to remember with NVIS antennas is that internal tuners, those packaged with the particular radio one is using, do not always work well in tuning NVIS antennas. I highly recommend using an external tuner for the best possible match. I use a Yaesu FT-857D radio with a LDG YT-100 external tuner and it works very well. The tuning on the 20, 40, and 80 meter bands is very quick. My antenna works well on 17-meters but takes a bit longer to tune up.
NVIS antennas have been around a long time and I don’t take any credit for inventing the things. I have used them with great success and love them. There are numerous designs for single-band operation and others for multi-band use. The important factor here is that being able to set up quickly and communicate during localized emergencies or worse will be a great “tool” for you as one that is serious about covering all of your preparation bases. My suggestion is that individuals build or acquire a good NVIS antenna, get on the air with it, find out who you can talk to, and exercise the thing often on various bands and modes. Get comfortable using your antennas and other amateur radio equipment. Set up nets and talk with other individuals who are preparing for whatever may come. Set up an amateur radio prepper’s club and have some fun in the process of preparing and training. Have a “build it” night with other like-minded hams in your area and build the NVIS antenna of your choice. 73 (Best Regards)
Matt Moody is a former Sergeant in the United States Marine Corps and a former Army Signal Officer. He has been a licensed amateur radio operator (Amateur Extra Class) for 36 years. He has been a Platoon Sergeant and a Platoon Leader/Team Leader. He was involved in numerous air assault operations in the late 70s and in Special Operations in the 80s. He was a member of the Marine Corps Base 29 Palms Shooting Team (’77-’79), shot in numerous Division Matches, and is sniper qualified. Matt is also a graduate of the rigorous Marine Corps Mountain Warfare Training Center and the Marine Corps Escape and Evasion (E&E) Course. Matt holds an AAS degree in Special Studies (Military Science) from Ricks College and a BS in Criminal Justice from Utah Valley University. He is a former Supervisor with the Department of Homeland Security (DHS) where he was assigned to the Salt Lake City and New York City (JFK) airports. He enjoys teaching emergency preparedness and communications courses to individual and groups.
© Matt Moody 2013