N.V.I.S. Antennas Simple low wire antenna 80/40 Meter 250/300 mile range The term NVIS was coined either late or just post Vietnam era, but the mode was understood and used much earlier.

Source Information Additional Reading: Homebrew AS-2259/GR NVIS AntennaBy N3OC Much of the homebrew construction principles in this article were inspired byW9WIS’s web site at: http://home.century.net/w9wis/NVIS.html More detailed information about the various versions and uses of the AS-2259/GR and its close cousins is on Brooke Clark’s web site at:http://www.prc68.com/I/AS2259.shtml A lot of information about the height and gain of NVIS antennas in on W8JI’s website at: http://www.w8ji.com/nvis_n_v_i_s_antenna.htm

N.V.I.S. Antennas The idea is to bounce the signal off the ionosphere and have it reflect straight down.  This provides a strong signal out to 200 to 300 miles in all directions.  This is the largest coverage area you can get with a single receiver transmitter without a repeater. 

N.V.I.S. Antennas Note that squad radios operating in the 30 to 88 MHz VHF low band are designed NOT to have long range to prevent the enemy from eavesdropping.  Classical H.F. radio using antennas on high towers is designed to provide long haul communications. 

N.V.I.S. Antennas NVIS is ideal at providing solid communications that fill the gap between these two modes, out to a radius of 200 ot 300 miles.

N.V.I.S. Antennas Military H.F. radios typically use a vertical whip antenna, like the AS-1320 on the PRC-47.  The whip works against ground by means of a number of radials.  The main lobe is at right angles to the centerline of the antenna or parallel to the ground. 

N.V.I.S. Antennas This works well for distances up to about 70 miles (ground wave) [FM 24-19 says 10 miles for a man portable radio and 15 foot whip] or for very large distances corresponding to one or more hops off of the ionosphere (greater than 300 miles). 

N.V.I.S. Antennas If the H.F. radio is located in a valley or jungle these whip antennas do not work very well and so the Near Vertical Incidence Sky wave antenna was developed.

N.V.I.S. Antennas

N.V.I.S. ANTENNA PARTS LIST

N.V.I.S. Antennas The ideal height would be 1/4 wave above a metal surface. The would put the main lobe straight up. If you don't have a metal plated back yard but instead have dirt for ground the depth of the effective ground plane will be some distance below the surface.

N.V.I.S. Antennas In sandy or rocky areas that may be very far down, in which case the antenna can be laid on the surface or buried.

N.V.I.S. Antennas When the height of the antenna is lowered the dirt acts as a resistive shunt on the antenna lowering the transmit efficiency and also lowering the receive noise.

N.V.I.S. Antennas The "D" layer gets charged by the sun on a daily basis.  So near noon it has the most charge.  The "D" layer has a resonance around 1.6 (? memory) MHz and that's where it has the highest loss.  The farther away from 1.6 Mhz the less D layer adsorption there is. 

N.V.I.S. Antennas So NVIS is not a mode that will work for the AM broadcast band.  This is also why most military field portable HF radios have a frequency range like 2 - 12 MHz.

N.V.I.S. Antennas The lower end is limited by the D layer and the upper end is limited by the NVIS mode since it's very difficult to put a dipole up a 1/4 wave in the field.

N.V.I.S. Antennas When radials are used with a whip antenna the coupling to the Earth is lossy.  Antennas that are balanced like a dipole have higher efficiency because they do not suffer from ground loss. 

N.V.I.S. Antennas NVIS antennas are about an average of 10 feet off the ground and do not suffer from ground losses.  Some NVIS antenna systems, like the Eyring, operate a foot or so off the ground. 

N.V.I.S Antenna

N.V.I.S. Antennas without a repeater This provides a strong signal out to 200 to 300 miles in all directions.  This is the largest coverage area you can get with a single receiver transmitter without a repeater. 

N.V.I.S. Antennas without a repeater The disadvantage is that the frequency needs to be properly chosen 1.8 to 12 MHz.   That can be done by using an on line propagation map, a chirp sounder, or ALE automatic link establishment radio.  HF-Link software works with HF Radios that have a computer interface. THE END

1995 ARRL AND ALE Your Tax Dollars at Work ALE is causing quite a commotion. Not only are government agencies excited, but private industry has jumped on the bandwagon in support of government contracts. Just when many government agencies were scaling down their HF operations with satellite and higher data rates taking preference ALE has arrived. A NEW BEGINNING? Ref: February 1995 QST Volume 79, Number 2 ALE THE COMING OF AUTOMATIC LINK ESTABLISHMENT By Ronald E. Menold, AD4TB