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The American Radio Relay League
Near-Vertical Incidence Skywave
(NVIS) HF Propagation
Greater Fairfield Amateur Radio Assn
September 12, 2016
Joel R. Hallas, W1ZR
Contributing Editor, QST
ARRL
Copyright 2016, Joel Hallas, all rights reserved
The American Radio Relay League
Traditional short-to-medium range communication:
Mobile-to-mobile
Mobile-to-base
Line-of-sight (LOS) – V/UHF
or MF, or HF, or optical
most anything works
The American Radio Relay League
Traditional short-to-medium range communication:
Mobile-to-mobile
Mobile-to-base
Line-of-sight (LOS) – V/UHF
or MF, or HF, or optical
most anything works
Terrain limited?
No problem –
put a V/UHF repeater on the mountain top!
The American Radio Relay League
Traditional repeatered short-to-medium range communication:
To have a repeater – you must own, control or hold the high ground!
And have power and security
This worked for most US forces in WW2 and Korea
But not in Viet Nam and the Balkans – very mountainous,
small pockets of US/NATO presence
The American Radio Relay League
Path of Radio Wave Via the Ionosphere
The American Radio Relay League
Path of NVIS Wave Via the Ionosphere
NVIS happens when transmission is below
the critical frequency for vertical radiation
The American Radio Relay League
The optimum frequency for NVIS is one close to the
straight-up Maximum Useable Frequency (MUF)
Higher frequencies go off into deep space
Lower frequencies get absorbed by the D-layer in daylight
What this usually means is:
40 meters in daylight
80/75 (or 160) meters at night
The American Radio Relay League
The American Radio Relay League
The optimum antenna for NVIS is one that radiates
at high angles – exact opposite from what is desired for DX!
This means horizontally polarized antennas that are less than
1/2 wave high – 1/4 wave is about optimum:
much lower, lower impedance and efficiency
much higher, more radiation at low angles, less at high
The American Radio Relay League
Typical Options for an 80 or 40 Meter Antenna:
Horizontal Dipole
Vertical Monopole
Ground
Half -Wave
Quarter -Wave
The American Radio Relay League
Elevation Pattern of a Horizontal Dipole at Different Heights
The American Radio Relay League
Azimuth Pattern of a Dipole at Different Heights
The American Radio Relay League
My Favorite NVIS Day/Night Antenna
40/50 foot fiber mast Parallel-connected
perpendicular 80/40
meter inverted V
Top view
The American Radio Relay League
My Favorite NVIS Day/Night Antenna
Modeled dimensions
40 foot fibre mast
8 feet 54 feet 26 feet
16 feet
The American Radio Relay League
Peak elevation patterns with 40 foot pole
The American Radio Relay League
60° Azimuth patterns with 40 foot pole
The American Radio Relay League
Elevation pattern of 43 foot Vertical on 80
The American Radio Relay League
Elevation pattern of 43 foot Vertical on 80, tipped 30 degrees
The American Radio Relay League
Elevation pattern of 43 foot Vertical on 80, tipped 45 degrees
The American Radio Relay League
What about mobile operation?
The usual vertical whip won’t hack it – low angle
Not enuf room for an 80 meter dipole, except on a ship
This calls for a high-tech solution!
The American Radio Relay League
The American Radio Relay League
The American Radio Relay League
The American Radio Relay League
The American Radio Relay League
The American Radio Relay League
The American Radio Relay League
Russian military communications
vehicle which uses an NVIS antenna system.
Photos by PA3EQB
The American Radio Relay League
USMC test
validates NVIS
reliability.
20 watts = 100%
effectiveness in
200 mile radius
The American Radio Relay League
Questions?
Give it a try!
The American Radio Relay League
A word from our sponsor –– ARRL books by Joel R. Hallas, W1ZR
New last Fall, “The Radio Amateur’s Workshop and Laboratory”
The American Radio Relay League
Headquarters, Newington, CT
Thanks for Your Attention!
© Joel R. Hallas, W1ZR
Technical Editor, QST
ARRL
