NVIS antenna - ARES: Gwinnett County

NVIS Propagation
and
Antennas
HF and Short Distances
© 2009 Stan Edwards, WA4DYD, PhD, GA CEM – Master Manager
(PE ret, MAJ USA Signal Corps ret)
� Introduction
Agenda
� Issues with short distance HF
propagation
� Antennas for NVIS Operation
Introduction
� Tactical operation vs. fixed operation
� Initial response
• Whip antenna
• Dipole antenna
� One antenna does not fit all
requirements
• NVIS antenna
• Long-haul antenna
7/2009
What is NVIS propagation?
“NVIS coverage has been described as
similar to squirting a hose with a
spray nozzle straight up thus
producing an “umbrella” of rain for a
substantial radius around the hose.”
– U. S. Army Field Manual FM 24-18; Field Radio Techniques;
Appendix N; December 1984
Why should we understand NVIS
Operations?
� It effects whether we can
communicate or not
� In emergency communications, we
must understand so we can maintain
continuous communications 24 hours
per day
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F2 Region
F1 Region
E Region
Near Vertical Incidence Sky-wave
Transmitter
Earth
Receiver
Impact of Solar Activity
Distance
0
25
50
100
200
300
SSN 10
2-4 MHz
2-4 MHz
2-4 MHz
2-5 MHz
2-6 MHz
2-6 MHz
“Employing an Antenna Family for Optimum Tactical HF Radio Effectiveness” by A. S. Christinsin, P.E., November 1973
SSN 110
2-5 MHz
2-5 MHz
3-6 MHz
3-9 MHz
4-10 MHz
4-12 MHz
Impact of Summer vs. Non-summer
Distance
0
25
50
100
200
300
Low Angle
(Other Than Summer Day)
90
85
80
70
55
45
“Employing an Antenna Family for Optimum Tactical HF Radio Effectiveness” by A. S. Christinsin, P.E., November 1973
High Angle
(Summer Day)
90
85
85
80
70
60
Issues
� On some paths, particularly unobstructed
short ones, ground wave propagation may
also be possible and interact with skywave
propagation - problem
� As path becomes shorter, MUF becomes
lower
� Lower frequency waves are more
susceptible to absorption
� As frequency lowers, noise levels go up:
5-8 db going from 40M to 80M; 8-9 db
going from 80M to 160M
Antenna Considerations
� Site Selection (skywave NVIS
operation – normally horizontal
antennas)
• Reasonably level terrain
• Foliage down at ground level under the
antenna and at least a half wavelength
around the antenna
• Shielding angles to the horizon should
not exceed about 45 degrees for 250
miles – higher angles for shorter paths
“Some Considerations Relative to HF Facility Siting in a Tactical Environment” by A. S. Christinsin, P.E., July 1977
Antenna Considerations
� Site Selection - General
• Away from high tension (>440VAC) lines at
least 1,000 ft.
• Away from low voltage (

Optimum Radiation Pattern
“NVIS antenna fundamentals”, Edward J. Farmer, Army Communicator, Fall 1994, p 19
Antenna Considerations
� Usual NVIS height objective is 0.1 to
0.25 wavelength
• 160M: 49-123 ft.
• 80M: 26-60 ft.
• 40M: 14-30 ft.
Possible NVIS Antennas
� Dipoles at appropriate heights
� Dipoles at compromise height
� Compromise dipoles at appropriate
heights
� Compromise dipoles at compromise
height(s)
� Poor man’s AS-2259/GR
� Whip pulled over so it radiates
upward
Compromise Dipoles At
Compromise Height
Compromise Dipole At
Compromise Height
AS-2259/GR
The
Buddipole TM
3

AS-2259/GR
Poor Man’s AS-2259/GR
A Poor Man's Portable Emergency NVIS Antenna System, W. Stanley
(Stan) Edwards, WA4DYD, Antenna Compendium, Vol. 7, ARRL, pp 9-11
Poor Man’s AS-2259/GR
Bent Whip Antenna
References
� Field Antenna Handbook, Prepared by James A.
Kuch, Department of Defense Electromagnetic
Compatibility Analysis Center, Annapolis, MD,
June 1984
� Various articles by A. S. Christinsin, PE who was
the Chief of the Air Force Communications
Systems (AFCS) Spectrum Management
Division and AFCS Command Frequency
Manager
� Various articles on NVIS operation from the
Army Communicator
Websites
� http://groups.yahoo.com/group/NVIS/
� http://www.globalsecurity.org/militar
y/library/policy/army/fm/24-19/
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