Hi Everybody,

Here is something to ponder...

When you want "Local" communications on HF, why use an antenna designed for DX (Distance) communications?


Isn't it silly (or worse ) to expect the antenna you are using to achieve the "Worked All States" (WAS) and "Worked All Countries" (WAC) Awards to be able to work for Local communications?

Enter "THE NVIS Antenna"
Near
Vertical
]Incidence
Skywave

Basically, we need an antenna that will give us usable HF communications in a 75 - 100 mile area (i.e. statewide) and the tri-state area.

Consider this:
Region 2:
The maximum straight line distance from any municipal EOC in R2 to the DEMHS R2 EOC is not greater than 42 miles.

Statewide:
The greatest straight line distance is about 114 miles.
- Greenwich (in the SW corner) to Thompson (in the NE corner)

THE ANTENNA
What we need to develop an NVIS antenna that can be used with our HF radios on the 75m and 40m Bands. It needs to be:
- Standardized,
- Easily duplicated,
- Transportable and quickly deployable.

A "Fan Dipole" /"Turnstile" antenna in various configurations:
- Inverted "V": with 20' center/8' ends AGL
- Horizontal Dipoles: at 10' AGL ?
- Horizontal Dipoles: at 2' AGL (stretched over traffic cones)?
OR...
- End fed wire (~ 33' for 40m) bolted to a mag mount on the car roof and stretched out to a tree (add another and a jumper for 75m)?
OR...
- Other ?

COAX
As with other HF antennas, the RG-8X ["Mini 8"] coax cable will be good for this application (dB loss/100' @ 3.5 MHz = .66 dB)
- Currently, you can purchase 100' of RG-8X for about $40 - $55.

WIRE
14 gauge stranded/super flexible copper wire for easier set-up and take-down.

LINKS follow...

75/ 60/ 40Meter NVIS Portable Antenna
www.eham.net/articles/5747


Make A Quick, Easy, Cheap, NVIS Antenna for Roadside Operating
- ”K.I.S.S.” (Keep It Simple Sherlock)
by D. W. Thorne, K6SOJ, SEC SV Section
www.emcomm.org/projects/nvis.htm


A Portable 75 / 40* Meter NVIS Antenna
by David B. Murray, KD1BL
www.starc.org/technotes/75-40%20meter-nvis.html


N.V.I.S. Portable Antenna
Stephen T. Reynolds (W4CNG)
www.eham.net/articles/4141


What's the Deal About "NVIS"?
Straw, Dean, N6BV
QST - Dec 2005


NVIS Antenna Design
Theory, Modeling, and Practical Applications
Ceburn Jack Swinden - W5JCK
www.w5jck.com/nvis/W5JCK-NVIS-Antenna-Presentation.pdf


NVIS ANTENNA THEORY AND DESIGN
Texas Army MARS
txarmymars.org/downloads/NVIS-Antenna-Theory-and-Design.pdf


Near Vertical Incident Skywave (NVIS) Antenna
Pat Lambert - W0IPL
www.w0ipl.net/ECom/NVIS/nvis.htm


Four pound Single Mast HF-NVIS and VHF Antenna System for Amateur Radio Emergency Communications.
Gary Wilson, K2GW
www.w0ipl.net/ECom/NVIS/K2GW-NVIS.htm


NVIS INFO
www.tactical-link.com/nvis_member_page.htm


W8JI - NVIS N.V.I.S antenna
www.w8ji.com/nvis_n_v_i_s_antenna.htm
(good myth debunking!

Discussion welcome.

I am impressed with these two designs (now, THREE - See next post):

75/60/40 Meter NVIS Portable Antenna
Steve Reynolds - W4CNG, DEC Metro-Atlanta, GA
www.eham.net/articles/5747

and

Make A Quick, Easy, Cheap, NVIS Antenna for Roadside Operating
- ”K.I.S.S.” (Keep It Simple Sherlock)
D. W. Thorne, K6SOJ, SEC SV Section
www.emcomm.org/projects/nvis.htm


I wrote to Steve Reynolds (W4CNG) last week, and he responded:

"The NVIS antennas are set up so the center of the antenna is no higher than 6-8 feet and the ends are just above the ground. That will give you coverage of 100 or so miles from the antenna.

Things like operating over rocky ground (granite or limestone) will affect the coverage.

You put up a 75/40meter dipole up over 15-20 feet, and you will go into DX mode at night.

NVIS on 40m works better in daytime, and 75 works better into the afternoon and evening.

YMMV as does mine."

I was thinking again recently of Rod Lane's (N1FNE) Patented Antenna Design for a shortened Dipole.

Versatile wire antenna and method
US 7864131 B2
www.google.com/patents/US7864131

Here is the top of the Abstract:
Abstract
A versatile wire antenna that can be up to 80 percent shorter than traditional wire antennas—while still providing exceptional operating characteristics.
The present invention:
- is also more durable than traditional wire antennas,

- offers broadband

- multi-band performance (with a tuner)

- eliminates tension on the wire components,

- does not require inductive elements,

- does not require end insulators or transmission-line feed-point insulators,

- has low noise characteristics, and

- offers the potential for significant static-discharge capability.

Also disclosed is a method for constructing the present invention.

BOTTOM LINE
What this means for ARES operations is an HF NVISantenna (and a tuner) for 75m & 40m Phone that is ONLY about 50 FEET long (vs.124 feet for a regular 75m antenna)
WOW!.

Be sure to go to the link (above) to read the rest of the Abstract and see the submitted drawings.

The minor challenge is to find a way to wrap up (fold?) the antenna for easy storage and rapid deployment.

Also see:
ctaresregion2.org/forum/antenna-central/...-antenna-project#219
ctaresregion2.org/forum/antenna-central/...-antenna-project#220

Eric - KB1EHE writes:

Hi all.
As Douglas mentioned in the Region 2 forum, the "Versatile wire antenna" that Rod / N1FNE and I invented and patented ( www.google.com/patents/US7864131) is a dramatically shorted horizontal antenna that makes a fantastic NVIS antenna. That's what I use at my QTH. In fact, I use the same antenna for both my primary multi-band HF antenna (for 160 - 10 meters) and for NVIS. It works that good.

Our patent gives only high-level construction details. Let me type below the actual method and components me and Rod use to construct our antennas:

The patented antenna design is the result of a number of years of experimentation with various wire lengths, number and size of the wire "triangles", and various wire-hanging methods. But feel free to experiment. If you come up with a novel variation that performs well, please let me and Rod know.

Use the above-referenced patent link for illustrations and general reference. Rod and I have discovered for a 160 - 10m antenna of this design, the total length of wire (prior to wire bending) that you'll need for the radiator is 128 feet. The wire is bent into equilateral triangles with two wire legs, each leg 6" long. To make those wire bends, in a consistent fashion, you can make a wooden or plastic triangle "form" or make a triangle pattern using three pegs in a wooden board. You can use almost any type of wire, stranded and solid, insulated or not. Wire types that are stiff enough to hold the triangle shape are generally preferred.

The end result will be a zigzagged length of wire. This zigzagged wire is supported by almost any common type of antenna rope. Almost anything you have will suffice. You'll need about 66 feet of rope for the resulting 64-foot zigzagged antenna element.

The zigzagged wire is supported by its triangle peaks. The wire essentially hangs on the antenna support rope like a shower curtain hangs on a shower rod. We have experimented with many ways of creating the support system. Our latest batch of antennas, which were quick and easy to construct and have proven to be exceptionally durable, uses nylon "mounting ties" (the zip ties with a screw mounting hole). They provide easy standoff / isolation from the support rope. Black nylon mounting ties (vs. clear) provide exceptional UV resistance -- and are thus very durable outside. Check out these at Home Depot: www.homedepot.com/h_d1/N-5yc1v/R-2025281...0051&catalogId=10053

Since there is no tension on the wire radiator, the antenna does not require a center insulator as in a traditional dipole. The feedline is attached in the middle of the entire length of the wire conductor, with 64 groundward-pointing peaks on each side. We typically just snip the central downward-pointing triangle and solder the feedline conductors to the two wire ends.

As for the feedline, we strongly recommend parallel-conductor "ladder line". From our testing, it performs very well -- and it is significantly lower in transmission loss than even the best coax. Unlike other antenna designs, the length of the feedline in this particular design is not critical. Any length is fine.

We typically recommend that the feedline is connected to an antenna tuner -- whether an external unit or one built into the transmitter. If the external / internal tuner does not have a parallel-conductor input, we have found that a 4:1 balun attached to a short piece (couple of feet) of coax makes a well-performing transition.

Note: Not only does the antenna design not require a central antenna insulator, it does not require end insulators either. The far ends of the antenna wire are just connected to the holes in the far-end mounting ties.

I hope this greater detail is helpful. I look forward to hearing everyone on the air in the NVIS Challenge!

73
Eric / KB1EHE

Also see:
ctaresregion2.org/forum/antenna-central/...nna-project/edit/220

Eric - KB1EHE adds:

Hi everyone.
Chet -KA1ILH wrote: "Think of a tri-angled slinky".

In this design, the wires are zigzagged in a single plane.
- With the antenna wire flat, in a single plane, it eliminates the inductor issues / problems of a slinky antenna. (The patent describes this benefit more fully.)

Thank you for the numerous kind thoughts and direct e-mails. Let me try to answer a bunch of questions in one swoop with a quick photo montage. I snapped the pictures below just a few minutes ago with my cell phone. I hope you find them helpful.

For my antennas, I use 1/8" three-strand polyester rope (but really anything will do). I open the braid, slip the nylon mounting tie through, then zip it up. Presto! I do this to the entire length of rope, 6" apart. So a total of 64 of them. I then feed the entire length of copper wire through and then, starting at one end of the rope, form the 6" triangles. It's a little tricky at first, but you'll find your own rhythm / technique.

NOTE: Instead of bending the wire using a form as mentioned in my previous e-mail, you can simply use a ruler and make bends in the wire every 6". Experiment to see which way you feel most comfortable. And if you discover a really handy way to do this, please let me and Rod know. We are continually experimenting with this portion of the process.

When you're done, the zigzagged wire will hang like a shower curtain; gravity will keep it there when the rope is taut. However, if you mount the antenna as a sloper or inverted V, or would just like a little more security to the construction, consider adding a mini nylon tie (those tiny 4" ones) to pinch the wire around the mounting hole. I made an antenna recently using this technique, and it came out great. And I noticed no difference in the on-air performance.

PLUS, if you want to make the antenna portable (like for emergency NVIS deployment), this extra mini nylon tie is a must. Otherwise, the triangle-shaped wire bends will slide around through the mounting holes -- and you'll end up with a tangled mess.

Once the antenna is constructed, and you want to wrap it up for portable use, I would suggest wrapping it around an empty plastic container -- like the gallon jugs for windshield washer fluid. (Again, make sure you use the optional mini nylon ties if you are creating a portable, quick-deployment version of the antenna).

If you have additional questions, let me know. Experiment and have fun!

Happy constructing!

73
Eric / KB1EHE