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Author Topic: NVIS (Near Vertical Incident Sky Wave) Communications for Emergency Comm.  (Read 2895 times)

MadMax

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I told Barb that I would be adding some “info” on this subject that folks interested in developing their “survival kills” would find useful..

I would like to start by defining what “NVIS” Near Vertical Incident Sky Wave communication is and why it is important for “Emergency” communications.

Many HAM radio operators like to “chase DX” that is put up the largest Tower and most expensive radio that they can afford to “contest” these events usually consist of making as many contacts as possible in a given short period of time. Points are awarded for each contact and many people are “on the air” at the same time in same frequency space making as many contacts as possible.

When we think about the power grid going down (and it will its just a question of when/how) we need some reliable way of communicating over “local/reginal” distances of say 300-400 kilometers or so. This is where a NVIS communications  setup comes in which is easy to do with VERY modest equipment. 

The Return of High Frequency: HF-NVIS, Your Regional Communications Lifeline When Everything Else is Broken

Author: Don Irving, NVIS Communications LLC

http://www.9-1-1magazine.com/Irving-RF-NVIS-Lifeline

The communications technologies that are available to public safety these days are more complex and powerful than we could have imagined a few years ago. Unfortunately, a side effect of increased complexity is greatly increased potential for vulnerability. Simply stated, the more moving parts in a system, the much more difficult the task becomes of identifying and plugging every possible scenario of vulnerability.  HF (High Frequency) and NVIS (Near Vertical Incident Skywave) provide a simple and reliable solution for backup communications over a wide regional area with no intervening infrastructure whatever.  It should be part of every public safety agency’s toolset for springing back after a natural disaster or terrorist attack.

Sobering Thoughts about Vulnerability

Natural disasters can disable almost every component of a communications system.  But terrorist attacks are potentially far worse. Think about the difference.  Natural disasters do not purposely target your systems; your systems just happen to be in the way.  Terrorist attacks, on the other hand, are intentionally crafted by technologically savvy planners to inflict the greatest damage to the most vulnerable components of your systems.

The 2009 “fiber cut” affecting southern Santa Clara County, California is an excellent example.  Unknown persons with technical knowledge of the area’s fiber networks climbed into manholes and slashed fiber cables that served entire communities.  9-1-1 operators and radio dispatchers noticed that their links were down.  People noticed that their land lines would not work, so they tried their cell phones.  Nope, sorry. Those were down also.  The fire department wound up patrolling neighborhoods looking for people who might be in need of 9-1-1 services.  Amateur radio

Why HF faded from public safety view

HF faded from the public safety view during the mid-1900s.  The main reason is that signal propagation in the HF range is complicated to understand and manage.  For any given time of day and state of the ionosphere, one HF frequency might work great to a particular location, but others will fail.  In the past this required the operators to be knowledgeable about the complex factors of HF propagation so that they could make sense of the current conditions and pick the best frequency. Ham radio operators delight in possessing this knowledge and using their skills to communicate.  But public safety organizations did not want to maintain a cadre of trained HF radio operators.  So when modern communications technologies came along for public safety, HF got relegated to the History Channel.


Summary

–>>  Every public safety agency needs multiple levels of backup for its communications systems. This should include a last-resort backup for the case where all other infrastructure is down.  HF-NVIS can provide reliable backup communications throughout a large regional area using absolutely no intervening infrastructure.  It is a technology whose time has come for public safety.

NVIS -Near Vertical Incidence Skywave: Why You Need It.

http://offgridham.com/2015/12/nvis/


NVIS is a transmission technique that allows for HF communications in the otherwise “dead zone” of 50-500 miles that is too far for VHF/UHF FM simplex, and too close for DX. For emergency & disaster purposes, DX is not particularly essential or even desirable. When sh*t Hits The Fan (SHTF), you are not going to care about being able to talk to Australia, or even the other side of the USA. –»  Most of your concern will be your immediate area, and extending outward, your geographic region.

For an off grid or disaster/SHTF application, you will not likely have the benefit of the internet to help you pick a frequency. In that case, you’ll have to rely on your wits and good old trial and error. In survival scenarios where you are coordinating with other stations, having a prearranged list of frequencies and a contact schedule is a must. My own experience is that 40 meters is good for NVIS almost any time of the day or night.



Near vertical incidence skywave

https://en.wikipedia.org/wiki/Near_vertical_incidence_skywave


Near vertical incidence skywave, or NVIS, is a skywave radio-wave propagation path that provides usable signals in the range between groundwave and conventional skywave distances—usually 30–400 miles (50–650 km). It is used for military and paramilitary communications, broadcasting,[1] especially in the tropics, and by radio amateurs. The radio waves travel near-vertically upwards into the ionosphere, where they are refracted back down and can be received within a circular region up to 650 km from the transmitter.[2] If the frequency is too high (that is, above the critical frequency of the ionospheric F layer), refraction fails to occur and if it is too low, absorption in the ionospheric D layer may reduce the signal strength.

There is no fundamental difference between NVIS and conventional skywave propagation; the practical distinction arises solely from different desirable radiation patterns of the antennas (near vertical for NVIS, near horizontal for conventional long-range skywave propagation).

The most reliable frequencies for NVIS communications are between 1.8 MHz and 8 MHz. Above 8 MHz, the probability of success begins to decrease, dropping to near zero at 30 MHz. Usable frequencies are dictated by local ionospheric conditions, which have a strong systematic dependence on geographical location. Common bands used in amateur radio at mid-latitudes are 3.5 MHz at night and 7 MHz during daylight, with experimental use of 5 MHz (60-meter) frequencies. Broadcasting uses the tropical broadcast bands between 2.3 and 5.06 MHz, and the international broadcast bands between 3.9 and 6.2 MHz, Military NVIS communications mostly take place on 2-4 MHz at night and on 5-7 MHz during daylight.

NVIS is most useful in mountainous areas where line-of-sight propagation at VHF or UHF frequencies is ineffective or when the communication distance is beyond the 50-mile (80 km) range of groundwave, and less than the 300–1500-mile (500–2500 km) range of lower angle sky-wave. Another interesting aspect of NVIS communication is, that direction finding of the sender is more difficult than for ground-wave communication (i.e. VHF or UHF). For broadcasters, NVIS allows coverage of an entire medium-sized country at much lower cost than with VHF (FM), and daytime coverage similar to MW (AM) nighttime coverage at lower cost and often with less interference.

Now that I have introduced the topic I will take about what kind of simple equipment can be used for this type of communications and how to obtain you “HAM” license in the shortest possible time..

Max.
"Ignorance is Bliss" - (Agent Smith the first Matrix Movie)

MadMax

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Now that we have defined the type of HF “communications mode” that is most suitable for emergency communications I would like to talk a bit about what kind of Amateur “gear” is most suitable/cost effective for this type of comms.

As far as antennas go “simple wire” antennas work VERY well, the other side benefit is just having them a few feet off the ground works for simple/quick setup and field deployment.

I can recommend two different wire antennas, I own both types and know/have meet the people from the small companies that produce them and both have GREAT customer service.

(1). Par EndFedZ® Antennas

 http://www.lnrprecision.com/endfedz/


The Par End-Fedz® are a full length half wave dipoles, but with an important difference. The coax connector is at one end of the dipole, where it is most needed. These antennas can be mounted horizontally, vertically or as a sloper. No ground plane or counterpoise is needed. Portable operation could not be easier. Simply hang the far end from a tree limb–the coax is at the bottom. Hang it up in a hotel window or string it up in the attic. End insulators are supplied making suspension easy.

HF EndFedz® (Patent Pending)

The UV resistant ABS plastic housing encloses an efficient matching network allowing the antenna to be fed with common 50 ohm coaxial cable. All hardware is stainless and the SO-239 connector is silver/teflon. The radiator wire is custom made for us in 21 mile runs. It is a #18 gauge stranded copperweld with a tough polyethylene jacket. Breaking strength is 200# and, unlike the vinyl jacket found on the vast majority of antenna wire, the polyethylene jacket is 100% UV stable, very tough and slippery – almost like Teflon®. One end comes with a #10 solder lug making attachment to the matchbox simple and allowing the radiator portion to be replaced if ever necessary. Power rating is a conservative 100 watts. Lightweight (the 20 meter version is only 0.5 pounds), they are ideal for portable work. The all black construction makes them difficult to see.

These are “single band” antennas work well and for the most part cost less than $100.00

Here are some reviews from “fellow hams” on eham.net

http://www.eham.net/reviews/detail/3632

Reviews Summary for LNR Precision End-Fed Half-Wave Wire Antennas

Fantastic Performer!     Time owned: more than 12 months
I wrote a review a long time ago, but I feel compelled to write an additional one. I initially got the 20m. Later, I got the 10/20/40m model. Finally, I bought the 40/20m version. It is 1/2 wl on 40m, and 1 full w/l on 20m. All of the antennas tune up easy. The 10/20/40 took a bit more effort due to the construction. People argue that it isn't any more special than other wire antennas. Getting to around a 1.0:1/1:1 at 49-51 ohms is a brag factor without much effort! Larry Draughon gave me some complimentary light gauge wire to try out when I bought the 40/20m. When hung from my Jackite 31' telescoping pole, you barely notice it, and the pole tip just slightly bends. The good thing about the 10/20/40m is that the matchbox can handle any resonant line from 10-60m. With some .26 gauge Silky wire from The Wireman, it gives you quite an arsenal to take into the field in just a couple of ziplock bags. Larry is always helpful with emails, and if in the office, never rushes to try and get you off of the phone. The previous owner, Dale Parfitt of Par Electronics, is just as helpful. I have one of his 6m OA-50 antennas at home. Even though he sold the EndFedz line, he will talk at length about them. I have found LNR Precision to be a very reputable company, with an above-average customer service. Granted, they are a bit expensive. But, they work great, are very durable and small. I think if you give one a try, you won't regret it. I knew that I liked it a lot, but I was considering getting either an MP1 by SuperAntenna or a Buddipole for portable. I was surprised by the number of people who bragged on the antennas, but noted that if given the opportunity, they would still rather have a Par EndFedz by LNR Precision.

(2). Portable HF Antenna 1.8-54 MHz


http://chameleonantenna.com/BASE%20ANTENNA/CHA%20EMCOMM%20II/CHA%20EMCOMM%20II.html

he CHA EMCOMM II Antenna has been specially designed for backup emergency HF system or permanent installation. The integral broadband impedance matching network (transformer 5:1) allows broadband antenna tuning.

It is the perfect backup antenna for apartments, condominiums, homeowners associations, deed restrictions and CCRs (Covenants, Conditions & Restrictions), ARES, RACES, MARS, EMCOMM, NVIS, First Responders and especially for Emergency Preparedness.

The unit is totally waterproof. The antenna is 60’ long and covers 6M to 160M. An external tuner is required

The antenna will perform very well with a sloper or an inverted “L” configuration. For a NVIS configuration (40M – 80M) the antenna must be installed horizontally with the ground and elevated between 9’ and 12’ high.

Here are some reviews of this antenna on eham.net

http://www.eham.net/reviews/detail/10895

60 feet and big performance!     Time owned: 0 to 3 months
60 feet and big ears? Who would have thought such a thing could happen!!
After a nearly 11 year hiatus from Amateur Radio, I decided to update my call after moving to Manitoba from Alberta Canada. When looking at antenna options, I was torn between a loop (40m) or a simple wire antenna, as my HOA has several restrictions and the lot also has issues, such as trees, which could interfere. After some deliberation and reviewing the other reports here on eHam.net, I decided to try the EMComm II antenna.

Carl was most helpful with several possible configurations of this antenna, and I finally decided on a simple 25 degree sloper off a 30 foot fiberglass mast, running NNE/SSW, with the feed at the SW end on the lower portion.

I have not even had this antenna a month yet and all I can say is... WOW! THis antenna gives big signals on the bands for what it is. Who would ever have thought I'd be reaching half way around the world, from The Pacific Islands to The Azores off the coast of Africa, and deep into S. America!

I get routinely 57-59 reports from the Carribean, 56 into western Europe (when bands permit) and even a 51 with heavy - and I mean heavy! QSB on 12m working a mobile station on the big island of Hawaii! All on 100W or less. Amazing.

Carl and his design group have done an excellent job designing this simple antenna to work well. It is very well made, all but invisible in daytime, and the Balun and choke system together with a good ground make this antenna radiate very effectively!

The key to success for me is two fold: one, the antenna should have a decent ground system, and I work off an elaborate radial counterpoise that is grounded in several spots on the property. Easy to hide those wires! Two, make sure that whatever you drive this with, that your modulation is good without distortion - that really goes for any system, but I find that the comments I am getting during heavy QSB fadeouts is that my signal holds right to the noise floor with Q5 copy. So, I thnk that this combination of good ground, and proper modulation techniques is a key to the huge successes I have had so far.

Less than a month, and I have over 100 contacts from Portugal, Azores, Cuba, Venezuela, Southern Brazil, Hawaii, and more! All from the heart of N. America: Manitoba! I think that this really says something about how well this antenna works!!!

I have two friends also returning to the hobby, and the EMComm II for one fellow and an additional choice of loop for the other is in their workings getting back on the air!

If you ever need a good, reliable, and simple antenna that works well, and is easy to hide and setup, the Chameleon EMComm II is a superb choice!!

I am looking forward to spending many cold winter nights at the radio logging warm locales from the confort of my chair! Thanks again Carl!

73 de Darren, VE4DL
Winnipeg, MB Canada


Next post I will discuss good “low cost choices” for HF emergency communications radios..

Max.
"Ignorance is Bliss" - (Agent Smith the first Matrix Movie)

ilinda

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Max, the stuff you are posting is like something out of a textbook.  Hope I can absorb at least some, or enough to participate and understand!  Thanks, BTW.

Yowbarb

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MadMax, well done on starting this Topic. This is all new to me and this is very much appreciated...
This sounds like  NVIS could be a real life- saver in the near future! :)
Members please post here your questions and help clarify anything you know about...

- Yowbarb

MadMax

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Ilinda;

 Sorry to be so heavy here with “technical details” let my try clarify some of what I have covered in the thread so far:

The going down of the power gird in North America will prevent most types of communication when cell phones, land lines, cable etc are “out of commission”. In such situations trying to “stay in touch” will most probably depend on some form of HF radio communications. This is in the frequency band of about 3-30 MHz. The AM broadcast band is below about  2.0 MHz.

In order to communicate over a region of out to 300-400 kilometers a simple HF radio setup can provide much needed communications. Here are two essential components:

(1). A simple wire antenna supported 6-12 feet in the air.

(2). A basic radio for communicating on the amateur segments of the HF HAM bands.

That is all that is required for usually reliable communications (when the power grid is down) and all other forms of communication are “out of commission”.

There are two very good wire antennas that I have mentioned above that would work well for this in the $100.00 price range. Next post I will provide details on a good inexpensive HF radio that I can recommend that works well and one that I use myself on a daily basis.

Hope this helps to clear up some of the “confusing technical details” that I mentioned in the above post.

Max.
"Ignorance is Bliss" - (Agent Smith the first Matrix Movie)

MadMax

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Here is a very good Youtube video on the “EMCOMM II” antenna and how it can be used for “Emergency Communications”

Commsprepper and Chameleon Antenna:

https://www.youtube.com/watch?v=Rn10eIREN20

Max.
"Ignorance is Bliss" - (Agent Smith the first Matrix Movie)

Yowbarb

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PLS keep on a keepin' on...
We all need to learn this stuff...
Also about what you posted easy ways to get Ham license...

ilinda

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MadMax, the only problem I have with all you are posting is that there is so much (!) and I'm sliding farther and farther behind in reading and absorbing all this.

In all seriousness, please keep up the great posts and hopefully there will be time enough to learn and implement what is needed.
Thanks for all this.

Yowbarb

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Here is a very good Youtube video on the “EMCOMM II” antenna and how it can be used for “Emergency Communications”

Commsprepper and Chameleon Antenna:

https://www.youtube.com/watch?v=Rn10eIREN20

Max.

Keep On Keepin' On...:)
MadMax - it's good to see  this info posted so  people can have a record of it and go through it and hopefully apply it. This could save lives so go ahead... Everyone will read, copy, print, understand at their own pace...
I am also behind on all this but to my way of thinking these alternate forms of communication may end up being the only way to stay in touch with, find loved ones...It could be too easy to get separated, even from people you are bugging out with, in all the chaos.
- AND - can you imagine what it would be like to travel hours to pick up a family member only to not be able to find them... knowing they could be within blocks of the location...not able to call them on the phone? So good to have a Plan B as far as communications.
- Barb T. 

Tiburon

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There are other options, in using local 2-way communications, simpler use and allow encryption for privacy.  Please respond to this post and I will elaborate.

 

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