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With the Australian call sign of
The quest to find and build Emergency Antennae
Emergency Near Vertical Incident Skywave
Being a relative newcomer to Amateur Radio I am keen to use my skills in times of natural disaster. Australia has a long and savage history of bushfires fuelled by years of drought and widespread flooding of some major river systems and with only 20million people living here, the emergency services can be stretched to capacity. That's why I joined WICEN. [Wireless Institute Civil Emergency Network] My local group is sponsored by the Bundaberg Amateur Radio Club.
Whilst Bundaberg WICEN increases its skills and equipment inventory to be able to respond where needed it seemed incumbent on me to also have a personal action plan. Bundaberg is considered sub-tropical so Tropical Cyclones are our biggest direct threat [between November & March each year] but there is also a Bushfire risk as we have some rugged national parks just to the West.
In 2006 Cyclone Larry devastated a town just to the north called Innisfail. Massive damage, No electricity or telephones and the need for Evacuation Centres gave our State a wake up call. As a result the authorities began a systematic rewriting of outdated disaster management plans. For us that means Bundaberg Regional Council, SES [State Emergency Services], EMQ [Emergency Management Queensland] and Welfare groups will need to draw all the resources together develop the plan. Whilst we hope it will never be needed, WICEN Bundaberg will be part of the planning and exercises - our aim is to be prepared.
So what do you need to be able to sustain communications in the event of no telephones (landline or mobile) and probably no electricity for several days?
I began to make a list; First get my amateur radio gear in order so an emergency station could be picked up and taken where it was needed.
Second; Build antennas that I could erect by myself.
Whilst training is great, we often have a group which includes some strong young men to do the heavy lifting - in the real world if I need to respond either at my own QTH or elsewhere, I need to be self sufficient yet still produce efficient radio signals if I am to be a viable emergency operator.
If you're reading this and you have pump-up masts, mechanical power and/or muscle power - this site probably isn't for you. But if you're not so endowed then read on because here's what I learned about building antennas that one person can erect without the use of tools [well OK you will need a hammer - but a rock or tyre lever would suffice]
The E.N.V.I.S. DIPOLE
I fell in love with this antenna when I first read about Bob Hejl W2IK and his dedication to emergency comms.
But wait... this is supposed to be a resource page, so let's go back to the beginning.........
What is N.V.I.S?
Definition: The Near Vertical Incident Skywave (NVIS) antenna provides the majority of its radiation at an extremely high angle. This means the major lobe is between 75 and 90 degrees to the earth's surface and will provide omni-directional communication for a distance of ??? - and here the experts disagree. Some say 400 Kilometres but some testing shows up to 1600km. Suffice to say we're not talking about long distances or DX however.
Why use an NVIS antenna?
Limitations or Disadvantages
Antennae that work well for NVIS
There is a “dead zone” of no signal between where the ground wave ends and where the sky wave came back to earth. This dead zone is called the Skip Zone.
The NVIS antenna is designed to send a signal into this Skip Zone – the previously dead zone. It is therefore designed for ‘short’ distance HF communications – the point being that during an emergency you do not want to communicate worldwide – you need to send your emergency messages within your own region/state/country.
2. Learn what factors influence your NVIS antenna performance: The frequencies and performance varies with a number of factors.
Well that's if folks, that's the theory - well as far as I'm interested in taking it.
Do some web research and check the modeling if you're so inclined. You'll find the proof that an NVIS Dipole at <3M is pretty impressive with constant omnidirectional coverage. See below for links to sites that gave me inspiration to build and test my own.
As I stated in the introduction, emergency communications was my goal - with antennas that were ‘quick & easy’ to erect – preferably single handed. Keeping the antenna height low, utilising the NVIS idea to put out effective signals ticked all the boxes for me.
Update: August 2012.
Based on the above research and design we made 3 of these antennas for our club [Bundaberg Amateur Radio Club] for use by the WICEN group. [That's "Wireless Institute Civil Emergency Network"]. In June 2012 the Queensland Police who head our disaster management organised an exercise "Contact 2012" and the group and these antennas were a resounding success. They proved HF communications between Bundaberg and Gayndah [120km] normall within the skip zone area of no signal.
Below you will find a pictorial diary of building the ENVIS Dipole, enjoy
Building an E.N.V.I.S. Dipole for 40 & 80M
What's with al the labels?
This is one antenna which might lay dormant for a time and memories fade - Clear labels speed up laying out your equipment
Also in emergency situations volunteers may help - Clear labeling reduces time and the frustration of running about a field wondering where things might fit
Time to think about storing and carrying the antenna - it's off to the sewing room
Here's a rugged duffel bag idea to store antennas - made from old jeans
2010 WIA National Field Day
In October 2010 the WIA called for a National Field day to field test emergency radio gear for the upcoming storm and bushfire season and to heighten awareness of Amateur Radio around the country.
This Field Day set for 12 hours 8am to 8pm, seemed a good time to test the radio gear & antennas in the emergency kit.
We have a good relationship with Century batteries so they loaned us 4 x 450ah truck batteries... yes it was overkill to power two Yaesu FT-857D transceivers but the fact is... we didn't know how many batteries we'd need - nobody has done this kind of testing in our club so what better way to learn than sit out in the sunshine all day and play radio.
We took Amp readings during the course of the day so now we have data and so do Century batteries. When we hold the next exercise, due in Late November we'll all know how many of the batteries to take out on site.
The batteries weighed 60kg each so the poor old farm vehicle became central to the Field station.
The E.N.V.I.S. Dipole was the star performer on the day surpassing the signals on the 40/80M Vertical.
There was nothing wrong with the vertical - in fact it was so well matched that it didn't need an antenna tuner but the Dipole was continually 2-3 "S" points above the Vertical.
VK4ION and VK4MAX worked the 12 hours and had a great time. We're lining up for next year for sure. Below are some photos.
The full story is at BARC FIELD Day webpage.
I wish to acknowledge the information from the following sources. Some helped me with antenna design, others with the background theory and modeling.
Bob Hejl W2IK - this man is a hero of mine. He loves emergency comms and just reading his pages will inspire you to want to build better emergency antennas. I've built several of his designs over the years and they all work! Sadly most of his individual pages seem to have fade from the internet. You may find info on his other great love the ArmyMARS Link
Pat Lampert W0IPL - A valuable N.V.I.S. resource with links to test results, modeling & antenna design
Dr. Carl O. Jelinek N6VNH [SK] - Designs for Inverted Vee N.V.I.S antenna
W2BLC Antenna Listing - Here you'll find a quick reference to most amateur radio antenna
Erecting the 40/80M Dipole
20 points to speed the process & ensure accuracy
These Notes refer only to setting up the Dipole pictured in the above photo diary.
1. Find a clear area 20M for 40M dipole [35M for 80M]
2. Decide on the Centre position of your dipole (according to your coax/needs etc) - Place a Pole Peg
3. Run stringline labeled 40M out from Centre peg - first in one direction - place peg at end of string
4. Using same stringline go out in the opposite direction - place peg [ You have 3 pegs in a straight line ? ]
5. If setting up for 80M band using the 80M extension Kit continue with;
6. At each ground peg lay out: 1 Blue pole : 3 nylon guy ropes : 3 tent pegs
7. Fit 3 [or 5] Poles over the Pegs - Do NOT extend poles - keep at comfortable working height. Near top of each pole: Locate metal tab with a hole either side - these take "closed C" clips with guy ropes.
8. Fit 3 white nylon guy ropes to each blue pole: Guy ropes have "closed C" clip on one end - to attach to pole.
9. Unfurl 40M Dipole antenna wire - TWO equal lengths - connected at centre in PVC Elbow with coax fitting
10. Fit PVC Elbow to centre pole - Fasten PVC Elbow to top rod using bolt/wingnut assembly. Tighten in position.
11. Tensioning ropes are attached to outer ends of the dipole wires
12. If setting up for 80M Band continue with:
13. Wire Jumper on 40M antenna wire is 300mm long. Ensure it will be able to reach the 'push-on' connector on the 80M extension wire
14. Attach 40M antenna jumper to 80M extension: Tension outer end of 80M antenna extension
Should now have Antenna Wire strung between 3 (or 5) poles and tensioned
15. Raise each pole individually - a little at a time if necessary, until at the required height
1.8metre (6ft) is recommended height for W2IK ENVIS Dipole
16. Tension and tie off guy ropes to secure all poles
17. Adjust antenna tension as required until all poles are vertical and antenna wire is reasonable taut
Don't overtension the antenna wire - a little line droop is acceptable
40M dipole is now ready for operation
18. If reflector [counterpoise] is required - use wire labeled "40M Dipole reflector [counterpoise]"
Run out Wire on ground - underneath & full length of the Dipole to act as reflector
Ends of Reflector Wire have 'push-on' spade connectors to attach 80M extensions [if being used]
19. If setting up for 80M band: Unfurl TWO Reflector [counterpoise] wires labeled "80M Ext. Reflector"
Lay reflector on ground under the 80M extension antenna
Push-on Connector at Inner End - connects to the outer end of the 40M dipole reflector wire - connect ONLY IF/WHEN the 40/80M antenna jumper on dipole antenna wire above is being connected
20. Safety: Yellow/Black warning tape: Unfurl & fix as required along full length of dipole.
Pink tape is tied onto Antenna Wire midway between each pole span to warn public of wire @ 1.8M.
"Non Ionizing Radiation" sign should be displayed near Transceiver/feedline
Stand back and admire your work - doesn't it look great ?
Now attach your coax transmission line, roll up a few coils to act as an ugly balun and run the coax back to your Transceiver