Introduction

Alpha Antenna offers four optional 35 foot NVIS Elements. The elements enhance performance of Groundwave, Near Vertical Incidence (NVIS) and DX. The 4 elements are for the HD-FMJ and ProMaster systems when mounted between 5 to 7 feet. The result is a Capacity Hat antenna with an enhanced omnidirectional pattern in the 70 to 200/300 mile range.

Enhanced Groundwave signal pattern

An omni-directional ground-wave pattern forms around the antenna when four optional elements are installed. Based upon terrain and frequency, the ground wave has a range of approximately 0 to 200/300 miles.

Enhanced NVIS signal pattern

The optional elements also provide higher take-off angles to enhance NVIS in an omnidirectional pattern.

Enhanced DX signal pattern

The optional elements also provide lower take-off angles to enhance DX in an omnidirectional pattern. DX will also be increased when there are no obstructions between the antenna and the horizon.

Analysis

The four NVIS Elements provides better SWRs as shown in the Analysis below, which enables this system to support spread frequency spectrum and band hopping requirements.

Installation of the elements

These four NVIS Elements are active elements, and attach to the top bolt on the Alpha Match near the Vertical element. The 4 NVIS elements should be evenly spaced once deployed and not lay on the ground, but be pulled out in the similar way that guy wires would be.

The 8’ grounded counterpoise then completes the circuit for the system. NOTE – The grounded counterpoise should not be placed directly under the NVIS Elements. It should instead be run between any pair of the NVIS elements.

The four 35 foot NVIS Elements are available here: http://alphaantenna.com/product/four-35-foot-wire-elements-usable-as-counterpoise-or-nvis/

Follow-up articles

How to choose the best HF antenna

How to choose the best VHF UHF antenna