eHam.net - Amateur Radio (Ham Radio) Community

Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net



[Articles Home]  [Add Article]  

75/60/40 Meter NVIS Portable Antenna

Stephen T. Reynolds (W4CNG) on July 6, 2003
View comments about this article!


NVIS Antennas for 75/60/40 Meters

By Stephen Reynolds W4CNG

A.R.E.S. DEC Metro-Atlanta Ga.

6-14-2003

This article describes an antenna support mast, and a 3 band antenna system just right for A.R.E.S. or other In-Field Deployment. The existing 75 and 40 meter HF frequencies currently utilized for A.R.E.S. - N.V.I.S. dictated that a simple antenna design to support the new 60 meter band was necessary. There are lots of articles and designs on N.V.I.S. antennas that use a tuner and ground connection. This system is band resonant, does not need a tuner to work, and is much more efficient in use. This mount assembly breaks down into sections of 1.5 inch schedule 40 PVC that are all 34 inches long. The length was chosen so that it would fit into a commonly available 36 inch duffle bag, and 3 sections of pipe could be cut from one 10 ft section of pipe with a small amount of excess left over. The picture below shows the pipe sections and center mount assembly.

0x01 graphic

The top section of the antenna is seen on the left with 4 additional 34 inch supports. The bottom frame assembly is to the right of the carry bag, with the 4 ground supports to the right.

Simplicity in design was the first thing, with a cost of less than $20 for the PVC pipe, and $4 worth of #14 stranded wire. Add 6 white end insulators (dog-bones), a center insulator (Alpha Delta), 4 Double Coat Hangers and you are ready to go at under $40 for a three band Resonant N.V.I.S. antenna. Add a carry bag at $15 if you do not already have a suitable way to transport the antenna. Red wire was chosen so that it would be easy to see, plus you may want to add yellow flags in a couple of places depending on where the antenna is deployed and whether ground traffic will go by it.

The next picture is of the center mast support assembly. I used 2 short 2.5 inch sections of excess pipe to join the T and 2 4-way joints. There are actually 6 different places the 4 ground supports can attach to. You chose the 4 you want to use. The two 4 way's need to be in line with each other and the T connection needs to be 90 degrees straight up.

0x01 graphic

I used end caps on the 4 ground supports, and 4 in line splices for the mast supports. This mount may be assembled (friction fit) using up to 4 center supports. This would have the center of the dipole at 15 feet above ground. The 4/6 dipole elements deployed will provide guying of the center support. You can deploy any two of the three dipoles or all three. Two dipoles will run at 90 degree spacing to each other. With all 3 dipoles deployed, they are at 60 degree intervals. Yes you can leave one dipole coiled on the center support without affecting the tuning of the others deployed. Standard dipole lengths worked. An antenna bridge was used to check resonance. 75 meters came out to be 63 feet on each end, 60 meters came out to be 42 feet on each end, and 40 meters was 31 feet on each end. Your lengths may vary with local conditions. I left 18 inches of fold back on each end of the dipole at the end insulators so that on site tuning could be done if necessary.

0x01 graphic

This is the completed mast assembly with one vertical support installed. If you are installing the system with 3-4 mast supports under it, you will want to unwind the dipoles you are deploying and have one person stand with the center mast while the ends are tied down. I use 3/16 inch black nylon rope for the end ties from the end insulators to whatever is being used to tie to. You can set it between trees, or in a small field and use tent stakes for tie down points. Remember to check tuning after installation. My antenna has +/- 75Khz on 75 meters, +/- 100Khz on 60 meters, and +/- 140Khz on 40 meters. Your mileage will vary. Using 100 watts on 75/40 and 50 watts on 60 meters, this antenna will work very well with very good efficiency because it is a tuned dipole.

Member Comments:
This article has expired. No more comments may be added.
 
75/60/40 Meter NVIS Portable Antenna  
by ID10T on July 6, 2003 Mail this to a friend!
A picture of what it looks like "deyployed" would sure interest me. Thanks for the article.

 
75/60/40 Meter NVIS Portable Antenna  
by N1RWC on July 6, 2003 Mail this to a friend!
That's neat. I have to agree with ID1OT as to a fully deployed pic would be awesome. Good Luck 73 Matt N1RWC
 
75/60/40 Meter NVIS Portable Antenna  
by KC2KCF on July 6, 2003 Mail this to a friend!
What are your experiences concerning mechanical stability of this setup in non-ideal conditions (e.g. reasonably strong wind gusts)? Judging by the pictures, I'm a bit concerned that the PVC joints may be twisted easily without using some struts or guy wire.

If this construction has proven to be stable, it might be handy for portable makeshift antennas in general (wire antenna support, or add a vertical whip, or even a small VHF/UHF beam, or ...).
 
75/60/40 Meter NVIS Portable Antenna  
by N4KRA on July 6, 2003 Mail this to a friend!
What a great Idea. handy and portable. I work the nuclear power plant drills here in W. Pa. As for stability, I made a target frame out of PVC and to hold it in place, I drilled a hole thru the ends of the legs and used the big gutter nails you can get. Give great stability then.
 
75/60/40 Meter NVIS Portable Antenna  
by W4CNG on July 6, 2003 Mail this to a friend!
I do not have enough room to deploy it at home. It looks like an X set-up with two bands deployed, and 6 wires with all 3 bands deployed. During tuning, I deployed only the two wires of each band and adjusted the center support to be directly under the two dipole wires. The dipole wires act as the guy wire for the center support. You may need a second person to hold the center support in windy conditions. When all dipole sections are deployed, it is quite sturdy.
Steve W4CNG
 
RE: 75/60/40 Meter NVIS Portable Antenna  
by K1MKF on July 8, 2003 Mail this to a friend!
My research shows that a 40m NVIS should be 10-20 feet above ground and a 75/80m NVIS should be 20-40 feet above ground. Anything below that will have significant ground losses. Your design looks good and as long as you realize it's a compromise antenna I think it's great for portable or emergency use.

MarkF
 
75/60/40 Meter NVIS Portable Antenna  
by N3IJW on July 9, 2003 Mail this to a friend!
I don't have anything to add, I just wanted to mention that your neighborhood has nice looking lawns :)
 
RE: 75/60/40 Meter NVIS Portable Antenna  
by W0IPL on July 9, 2003 Mail this to a friend!
http://home.earthlink.net/~w0ipl/nvis.htm
has a bit of information about height of the antenna.

Pat
 
RE: 75/60/40 Meter NVIS Portable Antenna  
by ROOT_ADMIN on July 9, 2003 Mail this to a friend!
must be astro-turn
 
RE: 75/60/40 Meter NVIS Portable Antenna  
by ROOT_ADMIN on July 9, 2003 Mail this to a friend!
damn keyboard..

astro TURF -- TURF
 
RE: 75/60/40 Meter NVIS Portable Antenna  
by VO1NO on July 11, 2003 Mail this to a friend!
Nice lawn.., nice homes... I'll bet you can't put antennas up because of covenants!

73
Al, VO1NO / W0
 
RE: 75/60/40 Meter NVIS Portable Antenna  
by W4CNG on July 11, 2003 Mail this to a friend!
You would not believe what I have in my 2600 sq ft attic that is 17 ft high, almost 30 feet off the ground. Full sized 75/60 meter dipole, DX-EE dipole, 2 meter Eggbeater, Diamond X-200 Dual-band antenna. Feeds to attic are 2 runs of Andrews 1/2 inch Superflex fed from a 1KW HF-30Mhz Station, with 150 watts on VHF/UHF. RF proximity issues are no greater than 6 feet below the antennas. Hard to beat with 2 sets of 10 foot floors under the attic.
Steve W4CNG
 
75/60/40 Meter NVIS Portable Antenna  
by KG4FET on July 15, 2003 Mail this to a friend!
This looks like a great idea for an easy quickly deployed emergency antenna! I am wondering though that if it were set up as a "Windom" if it would be better or worse. Sitting here playing with the calculator you can totally eliminate 2 wires and take up 1/2 the real estate (this is a safety item here). By doing the math using the formula's K4ABT has on his "windom" site you can come up with a windom for 75 meters, using the short leg of the 75 mtr windom add 1 wire @ 42.76 ft to other feed point and you have the 60 mtr dipole, go one step further and by using the short leg as the long leg for 40 mtrs add a 23.6 or ft wire and you have the "windom" for 40 mtrs. This is where the problem arises though. You would have to swap the feed line around for it to work on 40 mtrs. The Good things out weigh the bad (a 4:1 balun at the feed piont and a way to swap the feeds to work on 40 mtrs) though in that you have now made an antenna that is lighter (a plus if you have to walk a long way to the set up site), and takes up much less space (also a plus, less wires to trip over and take down if things get bad at the site.)73 and Nice job!
DE KG4FET Sandor
PS If you want a pic of the lay out described above I have as .BMP and would be happy to send it out. the Frequecies I used for the formulas are the ones most common for my personal use as 3.940/7.251/5.403.5(5.405)
 
75/60/40 Meter NVIS Portable Antenna  
by WB4NWS on August 15, 2003 Mail this to a friend!
Steve, great looking NVIS antenna. To answer one fellow hams posting, while the height may be technically correct for the respective bands, this is a NVIS antenna design. During actual ARES Drills, we have utilized the 75 meter NVIS at six feet off the ground and were able to communicate statewide, thus accomplishing what we needed to communicate throughout Georgia. We were also able to set the 59 feet of wire up with one end attached to my vehicle and the other end to a tree limb. Works great in the field! Thanks, Jim-WB4NWS, Cherokee County ARES AEC
 
75/60/40 Meter NVIS Portable Antenna  
by D104 on October 30, 2003 Mail this to a friend!
A compact and portable antenna. In reply to the question about stability, just put something heavy over the base. Be creative and use what is available: sandbag, bag of potting soil, bag of rocks, concrete block, etc. You can add two flexible plastic 5 gallon water storage containers as part of the kit. They add little weight or space when empty. Once you are on location fill them.
 
Email Subscription
You are not subscribed to discussions on this article.

Subscribe!
My Subscriptions
Subscriptions Help

Related News & Articles
The 'Wadetenna' for HF Pedestrian Mobile
How I Saved On My Tower


Other Antennas Articles
Using Yagis Backwards
The 'Wadetenna' for HF Pedestrian Mobile