The ¼ Wave Droopy Ground Plane 2 Meter Antenna
Filed under
Emergency Communication Posted by:
Rob Richardson
In the past we’ve talked about the many benefits of Ham Radio, and how every good survival plan should include some type of emergency communications equipment. When the power lines go down and cell phones stop working; the ability to send and receive information is going to be a critical factor in determining the outcome of your situation
In the coming month’s we are going to give some attention to the topic of emergency communication, and show you what it takes to communicate when the grid goes down.
Today, I’m going to show you how you can easily build a homebrew 2 Meter ¼ Wave vertical antenna for under $10. This antenna is perfect for HAMS that need a quick reliable solution for local 2 meter communication. It’s also a great antenna for emergency communication and can be fabricated and launched in a mater of minutes.
The ¼ Wave Droopy Ground Plane Antenna
ANTENNA PARTS LIST:
Keep in mind that this, and most HAM antennas, can be made with parts that you probably already have laying around your home. The parts below are what I used to build the antenna, but you can substitute most of these parts with whatever you have around your house.
- 1- 1 1/2″ PVC Pipe
- 2 – 1 1/2″ Adapter
- 1 -1 1/2″ Cap
- 1 -SO-239 Connector
- 50 ohm Coax
- Galvanized Utility Wire (16-14 Gauge) – Straightened and cut into 5 pieces (lengths below)
- 4 – 6-32 Stainless Machine Screws
- 4 – 6-32 Stainless Machine Hex Nuts
- 4 – #6 Crimp on Ring Tongue Terminals (16-14 Gauge)
Assembling the Antenna
The first thing I did was to assemble the actual working part of the antenna. To do this I cut and straightened 5 pieces of the galvanized utility wire down to about 20 inches.
To figure out the length of your antenna’s vertical and radial elements, you can use the following formula:
Length (in.) = 2808 / F
F= 146 mHz.
I used the middle of the band which is 146mhz. This calculated out to about 19.25”, which is what I eventually cut the wire down to when I had everything assembled.
Attaching the Vertical Element and Radials
Take 4 pieces of wire, which will be used as the antenna’s radials, and attach them to SO239 mounting holes using the machine screws and the ring tongue terminals.
Next, solder the vertical element of antenna to the center connector of the SO239 connector. After you are done soldering and connecting the radials, your connector should look like the picture above.
Final Antenna Assembly:
PVC – The PVC is used to stabilize the antenna so you can attach it to a tree, a tripod stand or anything that gets it up off ground. If you don’t have PVC, you can use any non-conductive material to build the base.
Take the 1 1/2” adapters and glue them to your PVC pipe; one on the top and one on the bottom (the bottom adapter can be used to mount the antenna to a flange for stability). Next drill a 5/8 inch hole in the top of your 1 1/2” cap and then attach it to the top adapter.
Slide the coax through the PVC pipe and connect to your SO-239 connector.
Bend your radials at a 45 degree angle; you now have a working antenna.
Antenna Performance
For under $10 worth of material, I was able to build a reliable antenna that can easily access all of the local repeaters with only 5 watts of power. At 25 watts, I was able to hit repeaters over 100 miles away.
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Very cool idea, but a word of caution. The center element is in a fragile position in this design. Perhaps cutting some cross lines in the PVC and putting a strain relief on the coax which you thread through a hole in a cap would allow the center element to be protected inside the PVC. Just a suggestion from a amateur operator who’s broken a lot of things
I agree. When I have the time I will probably go back and set it inside the cap.
The main point I wanted to get across was how easily an antenna can be fabricated. In an emergency, this antenna can be put together in a couple of minutes. For a long term solution, it would probably be a better idea to mount the connector inside the cap and run the wire out of 5 small holes drilled into the cap.
That was my first non rubber duck HAM antenna. It worked well for many years, until I replaced it with something better.
Can you get a close 1:1 SWR? And 2808inches, is that the full wavelength?
Full wavelength would be about 80 inches
If you put a small loop on the end of the top element, this little baby will hang just about anywhere! Paint it flat black and it is very stealthy with no mast.
How about a blob of hot melt glue around that center element for strain relief? You could build it up and it is cheap and non-conductive.
Now this is what we need, great ideas like this is why I enjoy this site so much!
Keep them coming!
My wife complains about the “ugly” antennas in the back yard. Because I love antennas, I would reply “There is no such thing as an ugly antenna.” But, I take it back, that’s an ugly antenna!
maximum utilization of available resources….is the key to survivability…….
Thanks for the post. As a fellow amateur radio operator, I’m always on the lookout for new and creative antenna designs.
Joe
Good idea and easy. Also by cutting to the correct length, a 440 antenna can be made the same way. How about a yagi design?
the length for a half wave is just 2X’s as long?
or 38.5 inches?
Yes… 2 meters is, well…2 meters or roughly 78 inches. So half of that would be 39. Since we’re not using the “top” of the band when we build antennas, 38.5 inches should be just fine for the middle of the band. You could, if you wanted, buy a mobile whip for a 5/8′s wave and cut it down to 38.5 inches and solder that to the center… I think your radials would have to change size at that point, too, though.
when the power lines go down and the cell phones dont work 90 % of all ham radio will no longer work either. only that run on mobile simplex and handhelds will still work. thats pretty limited. so at that point the nice ham rig just turned into a real pricey item with the effective use of a 50 dollar cb radio.