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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