A lot of hams are talking these days about Near Vertical Incidence Skywave (NVIS) propagation and the dipoles that can be easily deployed to take advantage of this mode’s in-state and next-state communication capabilities.
So, what’s all the buzz about?
NVIS uses high-angle radiation that sends signals almost straight up (hence the term, “near vertical”). The signals are then reflected back to Earth for effective short- to medium-distance communication that works virtually every day and into the evening, making NVIS antennas a go-to option during disasters or other emergencies, particularly in situations when repeaters, phones, and internet services are down. The military has used NVIS techniques for decades to provide short haul communication with other units on the ground. That’s why these “short skip” antennas are ideal for roundtable gatherings with regional ham friends on 80 and 40 meters. Additionally, NVIS dipoles…
- Are great for camping, RVs, QRP, State QSO Parties, Parks on the Air (POTA), and other uses where short-range HF operation on 80 or 40 meters is desirable
- Make a stealthy option
- Are almost omni-directional due to their near vertical radiation
- Have a legal-limit power rating
- Only demand a height requirement of having the feedpoint 15 feet above the ground
NVIS in Action
Close to home (DX Engineering headquarters are in Tallmadge, Ohio), the ARRL Ohio Section invited operators across the state to contact each other on NVIS Day, April 23. The goal was for hams to gain an understanding of how well they hear and can be heard using NVIS. You can read more about the event here.
DX Engineering 8040 NVIS Antennas
If you’re not inclined to gather the pieces and parts to build your own NVIS antenna, DX Engineering makes it easy by providing everything you need in handy full-size and shortened antenna kits.
Both the full-size DXE-NVIS-8040 and shortened DXE-NVIS-8040S dual dipole kits come with everything you need to build a high-performance NVIS antenna: fiberglass mast (four, 4-foot sections that extend to 15 feet); a DX Engineering Maxi-Core® 20 1:1 Balun, model DXE-MC20-1-1T; a balun mounting kit; coax strain relief bracket; antenna wire; insulators; four tent pegs; rope; and a 100-foot RG-8X coax assembly with PL-259 connectors. The four legs of the antenna, each deployed 90 degrees apart, provide the mast guying.
For a detailed look at what you receive and how to put the antenna together, check out the comprehensive instruction manual. It includes a complete parts list, tools required, assembly steps, instructions on setting up the antenna, notes on tuning it, accurate and detailed illustrations, and notes on NVIS propagation. From the instruction manual:
“A good NVIS antenna will not work well at DX distances. Antenna gain is a zero sum game. There is a fixed amount of energy radiating. If we push it all out in one direction (the near-vertical angles), we have to take it away from another direction (the low DX angles).
“Regular height dipoles or vertical antennas have a lower take-off angle and your signal may be heard three states away, but not in your state due to the skip zone. This skip zone is the area between the maximum ground wave distance and the shortest sky wave distance where no communications are possible. Depending on operating frequencies, antennas, and propagation conditions, this skip zone can start at roughly 10 to 20 miles and extend out to several hundred miles, preventing communications with the desired station.
With a ground wave, your signal does reach someone closer. A ground wave signal can go up to approximately 50 miles if conditions, including terrain and obstacles, are favorable.
“Using no skip zone or ground wave, the NVIS mode is used for making reliable HF communications below 10 MHz effective for a range to 600 miles. The NVIS propagation mode works best on HF below 10 MHz since these high angle radio waves are reflected back to Earth. Most often a low dipole is the best antenna to use and will provide reliable communications. This makes a NVIS antenna an excellent choice for emergency communications and for staying in contact with other amateur radio operators in nearby locations.”
Also available are the DXE-NVIS-8040SNM and DXE-NVIS-8040NM kits, which are exactly the same as the kits above except they do not include a mast. Simply use your own non-metallic mast or hang the feedpoint 15 feet above the ground from the limb of a tree.
- The shortened NVIS kits features loading coils to make the 80-meter dipole legs the same length as the 40-meter dipole legs, 34 feet, so this antenna fits into a square area that is only about 50 feet by 50 feet.
- The full-size kits feature 67-foot wire dipole antenna legs for 80 meters and 34-foot legs for 40 meters. The antenna fits into a rectangular area approximately 100 feet by 50 feet.
For more about NVIS antennas, watch Tim Duffy, K3LR, discuss the subject in this video from the DX Engineering YouTube Channel (please note that the video is from April 2021, so the special offers discussed are no longer applicable).
Also visit DXEngineering.com and check out the Chameleon CHA Hybrid NVIS Vehicular HF Antenna Base; the Chameleon MPAS 2.0 Portable Backpack Antenna System that supports a range of deployment configurations, including NVIS; the Chameleon EMCOMM-III-P Antenna; and K3MT’s book, Near Vertical Incidence Skywave Communication, Theory, Techniques, and Validation.
