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[Articles Home]  [Add Article]  

The NA4IT 'CHEAP' Dual Band Ground Plane

James "Scott" Duckworth (NA4IT) on December 3, 2003
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The NA4IT "CHEAP" Dual Band Ground Plane Antenna

Here is a neat little antenna that is very easy and cheap to build. It is ideal for Technician class hams needing a "first" antenna, and also a very good "emergency" antenna for use during Skywarn events when you don't want to be on the sky hooks tall in the sky! This little antenna is very functional on 2 meters and 70 centimeters.

Materials needed:
(1) SO-239 4 hole chassis mount connector
(3) 3/32 bare welding rods (copper or brass)
Rosin Core Electrical Solder
Clear Silicone Sealant

Tools Needed:
Heavy duty soldering gun
Wire cutters
Vise or "Third Hand" or another human.

The finished product will look like this:

0x01 graphic

Let's get started! From the welding rods you need the following:

(1) piece 25 & 1/8 inches long
(2) pieces 6 & 1/2 inches long
(2) pieces 19 & 1/2 inches long

Here is how to prep the SO-239 connector:

0x01 graphic

Now to make the vertical element:

0x01 graphic

Now take the 19 & 1/2" on one end, placing each on into one of the mounting holes of the SO-239 and crimp it tightly, then solder, filling the hole. The arraingement should look like this:

0x01 graphic

Here is a close up photo of the first one I did: (My 6" radials were made from a welding rod 12 12 & 3/4" long bent into a "C" shape and run down through 2 of the mounting holes, then bent back out to the proper angles and soldered.

0x01 graphic

Finish by covering the entire center pin and insulator area on the "top" of the SO-239 with Clear Silicone Caulk.

To mount the antenna, use a 1-foot piece of PL-259 connector up through the piece of conduit, connect the antenna to the coax, and let it sit down into the conduit. Use stainless steel hose clamps to attach it to a mast. I'm sure you can come up with other ways to mount the little antenna also. This antenna makes a great Severe Weather antenna, so that you can maintain communications, by mounting it in the attic or even below the eaves of your house.

The first time this one was used, it was used at a RACES drill. It was mounted to a small telescopic speaker stand by clamping the PL-259 to the stand with a single hose clamp. It was inside the building, and with 10 watts, we could hit both 2M and 70cm repeaters up to 30 miles away (and that's in East TN, the "Heart of the Smokies"!).

SWR results of the prototype were less that 1.5-1 on across both bands with 55 watts input. Your results may vary. Also, this antenna may be somewhat directional. Experiment with it. I would welcome computer-plotting results if some one would like to do them. Let me know how it works for you!

NA4IT, Scott Duckworth
na4it@arrl.net

Member Comments:
This article has expired. No more comments may be added.
 
The NA4IT 'CHEAP' Dual Band Ground Plane  
by KG4PFO on December 3, 2003 Mail this to a friend!
Neat.......I like it !
We need more articles like this !
Keep up the good work.
 
The NA4IT 'CHEAP' Dual Band Ground Plane  
by N9SC on December 3, 2003 Mail this to a friend!
I agree with the with the first comment left on this easy to follow construction project. Thanks for the nice job. I'm going to give it a try this weekend.
 
RE: The NA4IT 'CHEAP' Dual Band Ground Plane  
by VK4SX on December 3, 2003 Mail this to a friend!
Love it, great emergency antenna to have in the shed,
rgds
Dennis vk4sx
 
The NA4IT 'CHEAP' Dual Band Ground Plane  
by OK1FOU on December 3, 2003 Mail this to a friend!
Nice try, although a GP for 2 m band usually works for 70 cm as well (145 x 3 = 435) because . Similarly, a 7 MHz dipole works on 21 MHz etc.

73 Jindra
 
RE: The NA4IT 'CHEAP' Dual Band Ground Plane  
by VK3DMN on December 3, 2003 Mail this to a friend!
Whilst this is true as far as it goes when you use a vertical antenna on a harmonic (like the quoted 15m on a 40m vertical) or a 2m ground plane on 70cm the radiation angle is quite a bit higher.

This means that the power is being radiated to a large degree up towards the sky (which may or may not matter on 15m at various times) but it certainly matters on 70cm *grin*. This antenna would seem not to suffer from that problem.

This simple (but clever) variation on the basic quarter wave ground plane probably does exhibit directional effects (as stated by the builder) but this need not be a disadvantage, if this simple antenna was mounted so the mount could be turned then some directionality could be realised I suspect, which could actually be an advantage in certain situations.

I think I'll have to have a play with this design as well :-)
 
The NA4IT 'CHEAP' Dual Band Ground Plane  
by VE3TMT on December 3, 2003 Mail this to a friend!
Fantastic article Scott. I have built many 2m antennas this way, but your design for the 2/440 is soooo easy! Great pictures too!

Max VE3TMT
 
RE: The NA4IT 'CHEAP' Dual Band Ground Plane  
by STATICXD00D on December 3, 2003 Mail this to a friend!
Normally, the SWR can be adjusted by messing with the angle of the radials. Also, the monoband GP that I have has the ground radials connected via the little round, flat electrical connectors. They are then screwed to the SO-239 with small nuts and bolts. You can then remove them or even bend them all up for transportation. Of course, after bending them for a while the connector will break... but it's so cheap, keeping extra radiators on hand is no biggie!

Also, for very little more money, if one doesn't like the possible directivity of this antenna, one could simply build two of them, one for 2m and one for 440. Just make the single top wire straight up and down at the desired length (19" for 2m, 6" for 440), and make all four ground radials the same length. I've never used one for 440, but I have used one for 2m, and it works extremely well. You can bend a small hook onto the radiating element, tie a string to it, and pull it up into a tree and really get out with it!

Great article! I'm going to have to build one just because it looks like fun! Thanks!

73,
John N1JAC
 
RE: The NA4IT 'CHEAP' Dual Band Ground Plane  
by KB3KKT on December 3, 2003 Mail this to a friend!
Scott hit my favorite word with this one "cheap"

Thanks Scott
 
RE: The NA4IT 'CHEAP' Dual Band Ground Plane  
by KA4KOE on December 3, 2003 Mail this to a friend!
Man, this looks awfully similiar to that fan dipole everyone's raving about. If you did a whole bunch or radials out the top it would be a fan groundplane.

:) GOOD MORNING. Smile. Its only radio.

PHILIP
 
The NA4IT 'CHEAP' Dual Band Ground Plane  
by N3TTN on December 3, 2003 Mail this to a friend!
N1JAC Wrote: "Also, for very little more money, if one doesn't like the possible directivity of this antenna, one could simply build two of them, one for 2m and one for 440. Just make the single top wire straight up and down at the desired length (19" for 2m, 6" for 440), and make all four ground radials the same length. I've never used one for 440, but I have used one for 2m, and it works extremely well."



That's exactly what I did recently. My design is slightly different in some of the materials and construction, but very similar in some respects to the one in this thread. My radials and vertical element are from #14 AWG solid copper wire, and the SO-239 is mounted on a small "L" shaped bracket that can easily be attached just about anywhere with a "C" clamp or even vice grips. The vertical element is soldered directly to the SO-239. The radials are bent down at a 45 degree angle to help keep the radiation angle low. The radials and SO-239 are secured to the L bracket with 4/40 machine screws, so the whole thing can be disassembled quickly for transporting, and re-assembled on site, and this was important to me, because the radials and vertical are easily bent. Small red or yellow plastic caps from a Radio Shack SPST switch are glued onto the bare ends of the vertical element and radials to give the antennas a nice neat look, and they are less likely to poke holes in anything too. Performance wise, both the 2m and 70cm models I made had SWR's of 1.2 to 1 or less across the entire repeater portion of both bands, and a little higher at the top and bottom ends, but never more than 1.5 to 1 on either band. I can hit my local 2m/70cm repeaters located 20 miles away, on 5 watts with a full quieting signal, and nearly full quieting on 500 mw. All things considered these are good performers, cheap, easy and fun to construct, very portable, and with a little weatherproofing could even be a semi-permanent base antenna for emergencies or other situations where you need to get something up and running quickly and easily.


73, N3TTN
 
RE: The NA4IT 'CHEAP' Dual Band Ground Plane  
by KV4BL on December 3, 2003 Mail this to a friend!
...and with proper adjustment, this antenna may be configured so that it only works the CW portion of the VHF and UHF amateur bands....where the REAL hams are to be found.... OK, I DID IT, I DID IT,...I'm the first one to turn this excellent thread into a code vs no-code issue...now, where do I go to collect my prize? LOL!!! Seriously, this is a great article and more of this type are to be welcomed. Keep up the good work! This one is actually simple enough that I may give it a shot in the near future. 73, Ray KV4BL
 
RE: The NA4IT 'CHEAP' Dual Band Ground Plane  
by KA4KOE on December 3, 2003 Mail this to a friend!
Why can't you use metal coathangers instead of welding rods. Just scrape off the enamel?
 
RE: The NA4IT 'CHEAP' Dual Band Ground Plane  
by VA3EP on December 3, 2003 Mail this to a friend!

Yep, coathangers work just fine, have made 3 of them with coathangers, just have to file off all the crap (and maybe file down the size a little bit to fit inside the connector).

I also tried copper house wire, but it bends too easily for the 2 meter version. If you can scrounge the connector out of your junque box or at a flea for a buck or less, makes for an almost free antenna.

Here is another tip for the single element version: I had one break off where it was soldered into the connector, and when I re-soldered it I wanted to strengthen it a bit, so I hacksawed a short piece of the plastic barrel (not the ink cartridge, take that out) from an empty bic pen. I coated the area around the joint at the base of the connector liberally with epoxy and then slid the barrel down over that, making sure the cement oozed out at the top and around the connector, spreading with a stick.

When the epoxy cured it really provided extra strength at that joint. You would have to get creative with the two element version (maybe two pen barrels, sawed off at a 60 degree angle or something like that). The barrel is basically there to keep the epoxy in place till it cures.

Eric
www.va3ep.net
 
RE: The NA4IT 'CHEAP' Dual Band Ground Plane  
by K1RDD on December 3, 2003 Mail this to a friend!
I've also used those little flags that are used to mark water/electrical/cable lines in lawns. You can get them at the hardware store for about $10/100. They fit perfect into the SO-239. I also use V connectors on the arms with nuts and bolts instead of soldering. This makes it easier to store/transport. I've made a carrying case out of PVC pipe for mine (one end glued on, one end screw on). The only drawback to these flag posts is that they rust, but if you don't leave it outside it's not a problem.
 
The NA4IT 'CHEAP' Dual Band Ground Plane  
by NA4IT on December 3, 2003 Mail this to a friend!
I noticed in the article there are several typos that have to do with the HTML coding. If anyone would like, I will be glad to e-mail the original document I submitted to them. It is in Word format, with all the pictures and diagrams, and about 60kb in size. Just ask! Hopefully, the eHam editor will get the article fixed soon.

Also, someone had mentioned using clothes hangers. This can be done, however they are hard to solder and rust rapidly. The brass and copper rods do tarnish with time, but still function well. I have other antennas up that are made of them and they still perform well.

73 and thanks for all the good comments. (And if you want to prune it to work CW, that's fine too!) (grin)

Scott Duckworth, NA4IT
 
RE: The NA4IT 'CHEAP' Dual Band Ground Plane  
by KG6JEV on December 3, 2003 Mail this to a friend!
Nicely done article, Jim. Need more like this. This is what ham radio is all about, not arguing about code vs. no-code and who's a real ham and who's not.

73,

Steven
 
RE: The NA4IT 'CHEAP' Dual Band Ground Plane  
by KB9ERU on December 3, 2003 Mail this to a friend!
THIS is real ham radio. We need more articles like this one.
It's all to easy to just "buy" an antenna, but what is there to be learned from that?
I remember making my first 2m ground plane this way.
Great article!
Mick KB9ERU


 
RE: The NA4IT 'CHEAP' Dual Band Ground Plane  
by AG4RQ on December 3, 2003 Mail this to a friend!
I built a coat hanger groundplane using an SO-239 chassis mount connector and 5 pieces of straightened coat hanger. The radiator is 19.5" and the 4 radials are 20" each. It is actually designed for resonance at 146 MHz, but serves nicely as a dual-band antenna. SWR ranges from <2 to flat on all frequencies on 2m and 70cm. Construction is similar to N4AIT's, except there is only 1 radiator and all radials are the same length. As for the use of coat hangers, I built mine back in 1995. It is rusted through and through, but still performs as it did when it was new. I recently built another one, as I thought it was about time I replaced the original rusted out antenna. Ironically, the new one, although built exactly the same as the original (length of all elements the same) doesn't perform as well as my trusty rusty. Needless to say, the new one sits in the closet waiting for the day that the rusted 8 1/2 year old antenna disintegrates.
 
The NA4IT 'CHEAP' Dual Band Ground Plane  
by NA4IT on December 3, 2003 Mail this to a friend!
Here's an easier way to get a copy of the article if you want it.

HTML version
http://www.qsl.net/na4it/dbgp.html

or

WORD version
http://www.qsl.net/na4it/dbgp.doc

73 de NA4IT
 
The NA4IT 'CHEAP' Dual Band Ground Plane  
by KG4PRN on December 3, 2003 Mail this to a friend!
I have a variation on this design that some may find useful. I built one of these SO-239 ground planes some time back and at some point it fell over against a concrete floor, breaking off one of the radials. Resoldering turned out to be a pain, so the next version that I built, used 1/4 inch copper tubing for the radials. On each, I flattened one end and drilled a hole through it and used a 6-32 nut and bolt to attach it to the SO-239.

73 de KG4PRN
 
The NA4IT 'CHEAP' Dual Band Ground Plane  
by W3DCG on December 3, 2003 Mail this to a friend!
What a superb article! Excellent photo shots and graphics make it a joy to read!
 
The NA4IT 'CHEAP' Dual Band Ground Plane  
by AD7DB on December 3, 2003 Mail this to a friend!
This is a great article, Scott!

Just one other thing. Be sure to get the right silicone sealant. The preparations that smell like vinegar are corrosive and should not be used.

Dave AD7DB
 
The NA4IT 'CHEAP' Dual Band Ground Plane  
by WB6BYU on December 3, 2003 Mail this to a friend!
Great photos!

I recommend using brazing rod instead of welding rod,
however. The thin copper coating on welding rod rusts
off very quickly (in one case, overnight!) The steel
underneath is not as good of a conductor, and the
antenna has higher losses. In one case I measured the
performance dropped by about 10dB, though clearly this
will depend on the circumstances.

I generally use brazing rod for the vertical whip and
#12 solid copper wire for the radials.

If you want to experiment a bit, try soldering both
whips going vertical, but with the 440 whip soldered
to the ground side of the connector instead of the
center conductor. Adjust the spacing between the
vertical whips for best SWR on UHF.
 
RE: The NA4IT 'CHEAP' Dual Band Ground Plane  
by N8FVJ on December 3, 2003 Mail this to a friend!
I built one like it using the PL-239. Mine had a single whip & loads well on 2m & 70cm. It was so cheap, I feed it with 30 ft of high quality RG-8 foam coax. Being on top of a high hill, 70+ mile range is no problem with 50 watts. Works great!
 
RE: The NA4IT 'CHEAP' Dual Band Ground Plane  
by N6AJR on December 3, 2003 Mail this to a friend!
Bye the way.. if you mount this on a 10 foot piece of 1/2 inch thin wall electrical conduit, the little clamps they use to hold 2 pieces of pipe together in a run ( kind of a 1/2 twist clamp on both ends) fits over the outside of a standard uhf (pl259 style) connector( also 1/2 inch od). So drop te coax through the connector and the pipe and the little clamp gizmo hold it fast.

Also they make J shaped "nails" to hold these 1/2 inch thinwall pipes to the wall, and 3 or 4 of them will hold the 10 foot pipe and the antenna up above the roof line, also cheep. (but not a FAN DIPOLE)
 
The NA4IT 'CHEAP' Dual Band Ground Plane  
by W4WJH on December 3, 2003 Mail this to a friend!
Great article. We need more info like this to help us pass on our knowledge to the newer crowd of hams. Good job Scott.

Mike W4WJH
 
RE: The NA4IT 'CHEAP' Dual Band Ground Plane  
by K4JSR on December 3, 2003 Mail this to a friend!
Nice article, Scott. Just remember that folks who build their own antennas never die--
They just phase array!!!
Have a cool Yule and a Frantic First!
73, Cal K4JSR
 
The NA4IT 'CHEAP' Dual Band Ground Plane  
by K0RFD on December 3, 2003 Mail this to a friend!
Great article!

I have to agree with WB6BYU--Brazing rod is easier to work with, lasts longer, and is easier to solder.

I have built several antennas, ground planes and yagis, out of brazing rod. It's cheap, easy to solder, and doesn't rust. Let me also suggest that rather than using silicone to waterproof the center-pin connection, use JB Weld, an incredibly strong epoxy. It will add substantial mechanical strength to the center-pin connection, which is the weak point of the antenna (No, I DO NOT have stock in this company.) JB Weld even sticks to things like PVC pipe. It's glued every one of my homebrew antennas into position more or less permanently.

I have a 20-meter ground plane built almost exactly the same as what was described in this article (except that I used #14 solid copper house wire for the radiator and radials and hung it from a tree). It works great.

 
RE: The NA4IT 'CHEAP' Dual Band Ground Plane  
by N8VB on December 4, 2003 Mail this to a friend!
I built an antenna similar to this a few years ago using brazing rod. It is still up and still works fine. I used almost exactly the same arrangement on the vertical radiator but instead of 2 19" radials and 2 6" radials I used 4 20" radials. I think the arrangment using 4 20" radials will reduce the directionality even more, because part of the directionality comes from the non-symetric radials.

73,
N8VB
 
The NA4IT 'CHEAP' Dual Band Ground Plane  
by ND5Y on December 4, 2003 Mail this to a friend!
You can easily make a better antenna than that,
a combination 2m ground plane/70cm J-pole,
with the same construction technique and materials.

I got the idea here:
http://www.arrowantennas.com/gp146.html

I have one in my attic made from coppper wire and
an SO-239 connector and one (without
ground plane radials) on my car made from old
Larsen antenna parts.

The 70cm grounded 1/4 wave stub should be ~1 inch from
the radiating element and paralell to it.

73
Tom ND5Y

 
RE: The NA4IT 'CHEAP' Dual Band Ground Plane  
by VE3EGA on December 5, 2003 Mail this to a friend!
Scott,

Great little article and contribution to our hobby!

To Tom, ND5Y - just a suggestion, but why not follow Scott's article with your own pix of the described GP/J-Pole 'better' antenna???

Keep 'em coming

73

Terry
 
The NA4IT 'CHEAP' Dual Band Ground Plane  
by AD5KL on December 9, 2003 Mail this to a friend!
I've seen this before, but glad you reminded me of a great project. Going to put one in the attic, this is the perfect antenna for that. Would also make for a good dedicated weather-radio antenna, or for scanners.

I really like the suggestion about the bic-pen filled with glue to strengthen the vertical element.
 
The NA4IT 'CHEAP' Dual Band Ground Plane  
by KE4ZHN on December 12, 2003 Mail this to a friend!
Great little portable antenna for HT use or travel use. Cant beat something so simple and easy to make. Nice job!
 
The NA4IT 'CHEAP' Dual Band Ground Plane  
by AG4RC on January 4, 2004 Mail this to a friend!
Great article!

Soon after reading the article I was strolling through Wal-Mart and came across a 5-pack of brass-coated metal coat hangers for approx. 3-bucks.

The purpose for building the antenna was to compare performance / replace my existing 2-meter 300-ohm flat wire J-pole hanging down from the ceiling tile at work, 4-th floor office building.

Constructing the ground plane out of coat hangers was not too difficult and I mounted the antenna by hanging from the ceiling tile with a string - Like my original wire J-pole.

The results were surprisingly positive – Almost doubled my 2-meter range from my office!

With original wire J-pole I could hear approx. 4 local repeaters and “hit” approx. 3 local repeaters (with moderate noise to 100% full-quieting).

With the new dual-band ground plane I can now hear approx. 6 local repeaters and “hit” approx. 5 local repeaters (with moderate noise to 100% full-quieting).

Antenna performance comparison performed with an Icom (IC-V8) 2-meter HT running high power connected to an external home-brew 9.5V, 5Amp DC power supply.

73 - Peter
 
RE: The NA4IT 'CHEAP' Dual Band Ground Plane  
by K8MHZ on March 26, 2005 Mail this to a friend!
Just wondering...

Commercial antennas use radials that are usually shorter than the radiating element. I am wondering what effect keeping them the same size has.

I also wondered what effect switching the radials around 180 degrees would have. A quick look at the antenna makes me think that the angle of radiation on one side of the antenna would be too high, the other too low. Only the sides would have a horizontal take off, with the radiators dropping it to the desired angle.

My thought is that by switching them, the difference in angle may be affected, tests would have to be done to see if it is desireable or not.

This is a great test bed antenna as it can be changed and manuevered easily. It is also easy to make a co-linear out of it by adding a coil and some structual parts.

Another use...modify the antenna so that cheap mobile elements can be put into it. I found a 16 inch tall dual band mag mount antenna at a fest that was a 440 co-linear and a coil shortened 2m 1/4 wave that works great! Just the elements can be had for very few bucks...stick it on your 259 ground plane and viola!!! Base antenna!

The concept of using a 259 connector for the feedpoint of other home brew antennas is a good one too. Anyone know how they work in place of a balun?

Thanks for the great article.

73 de K8MHZ
 
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