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4/25/2015 1
Presented by:
Clackamas Amateur Radio
Emergency Services
(CARES)
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NVIS Near Vertical Incident Skywave
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Introduction
In this class the basic techniques in the theory, use, and making of a NVIS antenna will be presented
Instructor:
David Kidd, KA7OZO
Emergency Coordinator (ARES)
Clackamas Co, Oregon
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Training Points
What is NVIS?
How will it work for us?
How hard is it to use?
Why should I use it?
What does it really do for us?
What materials are needed?
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What is NVIS…
NVIS is a combination of radio hardware,
sky wave radio propagation, operating
procedures, cooperation, and knowledge
used by a group of radio operators who
need reliable regional communications.
NVIS fills the gap between line-of-sight
ground wave and long-distance "skip"
sky wave communications.
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Propagation Theory
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NVIS Effect
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300 Mile Coverage
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Dual Band
Yes; you can remove the 60 Meter elements!
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How It Went Together
Materials
Construction
Modifications
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Parts List
1 - Feed point - 50 Ohm
#14 insulated stranded wire – 280’
3 - ½” x 10‘ PVC cut to length
2 – Insulators
Tie wraps
3/16” rope cut to length
Coax to the shack
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Spreader Lengths
2 – 17” Next to center
insulator
2 – 34” 2nd from center
insulator
2 – 50.5” End of 40 M element
2 – 25.25” End of 60M element
Another spreader could be used
between the center insulator and the end
of the 40M element
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Element Lengths
75 Mtr legs = 57.33 ft
60 Mtr legs = 45.4 ft
40 Mtr legs = 34.25 ft
Prune these lengths to meet your ground conditions
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40 Meter Tension
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Tensioning method for 40M
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Spreader keepers
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60 Meter tension
UV resistant line
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60 Meter Tension
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Beamwidth
75 Mtrs 38 deg. To 142 deg.
60 Mtrs 36.5 deg To 143.5 deg.
40 Mtrs 34 deg. To 146 deg.
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Night Time Ionosphere (300 mi.)
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Hints & tips
Solder wires at the feed point
Solder feed point pigtail to all other wires
Dipole insulator has an eye bolt in the top for
suspension from a tree or skyhook
Coax should be perpendicular to the antenna
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Choke balun – 18’ coiled 9-10 turns
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Hints & tips (cont.)
Ground conditions will drive element lengths
Wet vs.. dry
Use an antenna analyzer!!!
Tune 75M first, then 60 then 40M
There is interaction between the 60 & 40
meter elements
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Reflectors
Ground wires laid directly under
the antenna
5 Total!
1 on 75M and 2 each on 60 & 40M
Spacing is important – 2.5”
60M on either side of 75M & 40M
on the outside of 60M
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Tri-band Reflector Lengths
75M – 65’
60M – 47.9’
40M - 35.6’
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Dual Band Element Lengths
75 Mtr legs = 59.7 ft
40 Mtr legs = 35.25 ft
Prune these lengths to meet your ground conditions
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Dual Band Reflector Lengths
75M – 62.5’
40M - 37.25’
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60 Meter Considerations
USB
2.8 kHz bandwidth limitation
5 Channels (Window freq. -1.5 kHz)
100W ERP limitation
Antenna gain
Feedline loss
QST Feb. 2004 or ARRL FAQ
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Regional 60 Meter Agreement
5405 Nation/International
5373 Washington
5368 Idaho
5348 Montana/Oregon
5332 Regional coordination between
states/sections
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NVIS
Antennas are nondirectional,
Antennas designed for High angle, beamwidth
may be 30 degrees or more, greatly determined by
antenna height
Refracted back in circular pattern
Radius depends on strength and D/E layer
absorption
Ground wave can help/hinder NVIS skywave,
due to phase relationship
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Omni Pattern
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What is NVIS…
German ground forces first documented
NVIS techniques in WW-II
NVIS was more fully documented,
studied, and used by US forces in
Vietnam
NVIS is still used by today’s military in
combat operations
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What is NVIS…
NVIS propagation is generally
considered to be F-layer ionospheric
reflection at angles of 70-90 degrees
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How will it work for us?
Emergency groups such as ARES and
RACES are studying NVIS propagation,
techniques, and equipment deployment
for emergency preparedness.
NVIS is the tactical communication
system of choice in mountainous areas,
any areas without complete repeater
coverage, and all situations where
repeater-based systems have failed or
might fail.
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How will it work for us? (Cont)
With the recent release of manufactured
mobile and even portable HF radios, HF,
and antennas employing NVIS
propagation, it should become much
more popular and useful for disaster
tactical communications.
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What can NVIS do?
This is a mode of HF radio equipment deployment that allows for reliable communications within a range of 0-400 miles, and depending on condition even farther out.
NVIS can be viewed more as a "Systems Concept" and not just what antenna to use.
The concept of NVIS is to have reliable communications anywhere within an 800 mile diameter circle. Your station would be located at the center of this circle.
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How hard is it to use?
NVIS is not just an antenna type or a propagation mode -- it is a tactical communications system that was designed by military radio operators in the field.
The NVIS antenna is only part of that system. The other part is the knowledge and cooperation of the operators, which must be accurately applied to achieve the best results -- particularly when used in life-and-death situations.
Training and coordination is a key factor in making it all work properly.
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How hard is it to use? (Cont)
Emergency communications should be driven by clearly written procedures that have been well-designed and tested.
The procedures should be drilled on a regular schedule. The drills should be followed by debriefings attended by everyone, so that all can learn to avoid future mistakes.
Suitable procedures are available in books, Field Manuals, and on the web. Look for ARES and RACES web sites and capture their procedural documents. Other excellent sources are FEMA and MARS sites.
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Why should I use it?
To talk close in: under 200 miles
To have good overall state
coverage
To have multiple frequency
capabilities
To have a system that will work
under poor band conditions
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Main Reason To Use It
First and foremost, to completely
eliminate the skip zone. This enhances
all forms of local and regional HF
communications, for all practical and
experimental purposes.
Most of all it can be used effectively for
emergency operations within a local
geographic area.
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Among the many advantages of NVIS
NVIS covers the area which is normally in the skip zone, that is, the area normally too far away to receive ground-wave signals, but not yet far enough away to receive sky-waves reflected from the ionosphere.
NVIS requires no infrastructure such as repeaters or satellites. Two stations employing NVIS techniques can establish reliable communications without the support of any third party.
Pure NVIS propagation is relatively free from fading.
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More Advantages
Antennas optimized for NVIS are usually low. Simple dipoles work very well. A good NVIS antenna can be erected easily, in a short amount of time, by a small team (or just one person).
Low areas and valleys are no problem for NVIS propagation.
The path to and from the ionosphere is short and direct, resulting in lower path losses due to factors such as absorption by the D layer.
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Still More Advantages
NVIS techniques can dramatically
reduce noise and interference, resulting
in an improved signal/noise ratio.
With its improved signal/noise ratio and
low path loss, NVIS works well with low
power.
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Disadvantages of NVIS operation
For best results, both stations should be
optimized for NVIS operation.
If one station's antenna emphasizes
ground-wave propagation, while
another's emphasizes NVIS propagation,
the results may be poor.
Some stations do have antennas which
are good for NVIS (such as relatively low
dipoles) but many do not.
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A Few More Disadvantages
NVIS doesn't work on all HF frequencies.
Care must be exercised to pick an appropriate frequency.
The frequencies which are best for NVIS are those where atmospheric noise is a problem, antenna lengths are long, and bandwidths are relatively small for digital transmissions.
Due to differences between daytime and nighttime propagation, a minimum of two different frequencies must be used to ensure reliable around-the-clock communications.
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What materials are needed?
Materials are dependent on which
antenna type you want to use
Dipole fixed or portable position
Ham stick rotating dipole
Military type 2- band version
We will discuss material required
for each type
All are simple to make and use
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N6VNG’s NVIS Antenna
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Parts List N6VNG’s NVIS • 2 ea. 1.5" PVC pipes 7.5' long
• 1 ea. 1.5" PVC coupling
• 1 ea. 1.5" PVC cap
• 4 ea. Egg type insulators
• 5 ea. Brass Screws, nuts and washers to fit coaxial fitting
• 1 ea. SO-239 or UG-266 female panel-mount connector with
solder pot center pin
• 5 ea. Stakes (One at the mast center)
• 4 ea. Heavy solder lugs to fit brass screws
• 150' Antenna wire
• 60' Nylon rope
• Coax to rig. As much as you need. Run it up the center of the
PVC pipe mast and connect to the panel-mount
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Construction Notes: N6VNG’s NVIS
• Drill PVC cap to accept SO-239 and 4 screws and nuts
• Mount SO-239 to PVC Cap with screw heads down
• Cut off the head of a brass screw
• Solder a brass screw to center post of SO-239
• Cut antenna wires to length plus a little
• Fit one end of each wire with solder lugs
• Fit the other with the egg insulators
• Install wires to SO-239 using brass nuts and washers
{as shown in the figure}
• Erect antenna (2 men ~ 5 minutes)
• Tune antenna match for minimum VSWR
(also could adjust mast height and wire lengths)
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Dual "Ham Stick" version
Configuration that shows promise for ARES/RACES is to take two mono-band mobile antennas and mount them base to base, with one being the driven. element and the other being the ground side.
Care must be exercised in tuning this configuration that the elements are the same length.
They are light weight, portable, fairly inexpensive, and easy to put up.
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Dual "Ham Stick" version
This antenna is available at HRO.
Antennas are Ironhorse IHF80's and
IHF40's (two each) and the Ironhorse IH-
DAK-AD adapter
Total cost for four antennas and the
mounting bracket is $123.75 (as of 2/21/06).
You can use a Radio Shack tripod and
five foot mast sections for simplicity or 4
sections of cammo poles.
Plus a run of coax
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40m Rotating Dipole
KC7TOF’s rotating 40m dipole
and masting configuration
Very easy to set up and get on the
air
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Frequency Possibilities & Modes
40 meters during the day
80 meters at night
160 meters at night if 80m is out
The new 60m band with it’s power & antenna limitations can be very effective using NVIS techniques.
Desired modes: SSB, RTTY and PACTOR
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Multi-Band NVIS
40m, 80m, & 160m
170’ #14 stranded wire @ 30’ with
a tuner
Budwig Hye-Que type connector -
$7.95 @ HRO
Insulators - one pair @ $1.95
UV resistant rope for support as
needed for antenna site
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Real Life NVIS Use
Fixed dipoles at appropriate height
Rotating portable dipoles using
Ham Sticks
Military styled “X” version with 2
band capability - portable/fixed
position
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In Reality . . .
Groups of operators using NVIS must understand and cooperate on the basics.
All must be using NVIS antennas (defined as any horizontal antenna well under a quarter-wave high), as well as the radio hardware and propagation theory.
All must understand that the frequencies used must stay between the total absorption and vertical MUF ranges.
The group must decide whether it will equip itself to use 160.
Calling frequencies and other procedures should be established, in writing, with contingencies clearly stated.
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Actual Field Operation & Test
SET - 9/25/04
In parking lot
adjacent to new
county office
building on Kaen
Rd.
KC7CJO’s military
version antenna on
loan to CARES
Worked great!
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Personal Experience
80 meter horiz loop
Using on 75 Meter at 3.937 & 3.965 with tuner.
Work regional nets
• Net controls in:
– Seattle – 200 miles
– Hermiston – 180 miles
– Coeur d’ alene, ID – 380 miles
– Kelowna, B.C. – 480 miles
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What This Means
NVIS works
It is simple to make and simple to use
NVIS will fill the gaps during poor propagation and conditions
Minimum NVIS capability will cover the entire state of Oregon
NVIS can reach the capitals of the adjoining states of CA, NV, WA, & ID from our county
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Next Steps
Since you now know the basics of
NVIS, it is time to put your
knowledge to use
You can make one, buy one, or
borrow one . . . Just try it and I
know you will become a believer
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Links to NVIS URLs
www.qsl.net/wb5ude/nvis/
www.athensarc.org/nvis.htm
www.w0ipl.com/ECom/NVIS/nvis.htm
www.co.missoula.mt.us/acs/ACS/NVISp
age1.htm
www.co.missoula.mt.us/acs/ACS/N6VN
G%20AS2259.htm
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Presentation Credits
“What’s the deal about NVIS”? By Dean Straw, N6BV, QST Dec 2005
“NVIS Operations” by Ed Farmer, AA6ZM, QST, Jan 1995
“The NVIS - A Low Antenna for Regional Communications” by Albert Pion, KK7XO, QST, Jun 2002
“NVIS” by Norm Fusaro, W3IC, internet PPP
“Understanding NVIS Antennas & Propagation” by Harold Melton, KV5R, 2002, 2006
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Just about the end…
Questions ?
Thank you showing interest in
NVIS antennas!
I look forward to helping you get
started with your NVIS antenna
project