Basic Antennas for VHF-UHF Field Communications part 1

You have your first radio for some time now, you want to increase its performance in the field and also make a better radio kit for it. If you haven’t heard or read yet, the three most important words in radio communications are: Antenna, Antenna, Antenna

(which are followed by the next three: Location, Location, Location)

So, let’s see what your starter antenna options are . And that means simple, economic, easy to deploy -or even make- radio antennas for the VHF and UHF bands.

 

The Groundplane

It is the antenna that uses an artificial “ground” to work. In a base antenna the “ground” is the 3 or 4 radials that extend from its base. In a mobile (car) antenna the “ground” is defined by the car’s metallic body.

So a way for a ready-made option is to take a mobile antenna (that is already pre-tuned) and create its ground yourself.

One option is to get a magnetic base antenna and nail a metal sheet on top of a pole. This can be a lid of a paint can, a cookie baking tray etc etc. Then you stick the magnetic mount antenna on top.

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Nagoya UT-308UV 22-Inch Magnetic Mount VHF/UHF Antenna 

Then there is the ready made option. Remember what I said about metallic car bodies? Well the metal is getting scarcer on cars these days, so there is a ground-plane kit available for car antennas now.

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So one assembles his screw mount car antenna, the radial kit and the cable, and hoists them from a tree, or puts them on a tripod or on a stick. And he is only using what he already has in the car.

A.H. Trimble writes about this method in his blog.

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Great minds think alike and I have already done the thing some years ago by making a in-between connector with radials attached on it, for my mobile antenna and the cable.

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You can see more pics in this photoalbum

Notice the way this antenna is hoisted. The cord is tied on the antenna base which can handle the weight of. And I use a slipknot on the antenna top just to keep it vertical.

 

The DIY Quarter-Wave Groundplane Antenna

One can make an easy design, called the “one-Quarter-Wave Groundplane Antenna”. This  is one of the basic/starters antennas every HAM should try and as you can tell it is a simulation of any base antenna.

GndPlane2

Image Source

It requires minimal tools, materials and skill in building it. But the making of any DIY antenna involves “tuning” its length to the frequency. And it requires a validation of the make by some specific measurements taken with an antenna analyzer or at least an SWR meter. The latter is a device that measures antenna losses due to poor dimensions (actually returned back (reflected) power which is dangerous for your radio), and it is the easier to purchase and use.

You are basically getting a SO-329 chassis connector, which has 2 screw holes to be mounted on a radio chassis. Then you add 4 radials and the radiating center element. If you are a survivalist or a prepper this kind of connector you should stock some of.

Quarter_Wave_Ground_Plane_detail_M0MTJ

Image Source

And here is my take on the Quarter-Wave Groundplane. I wanted the radials easily removable, so I soldered electrical EU cable connectors on the center of a “UHF female-to-female” adapter.

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There is a boatload of instructions for building such an antenna but the following are what I selected:

 

The Jungle Antenna for the VHF band

The jungle Antenna is a makeshift antenna suggested by the US Army Manual. It is made out of another’s antenna elements or by antenna field wire that are readily available to the fighter.

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As you can see it is a variation of the Quarter-Wave Groundplane. And following the same idea and pattern one can make one for VHF out of simple wire like I did.

This is my build: The GR-P ¼-wave Ground Plane Wire AntennaOn the left you can see the dimensions in as fraction of the wavelength, 1/4th of 145MHz

And this is a connector that allows one to easily connect the radiating and the “ground” wires.

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If you can strip a wire and measure a length, you can make this antenna. Just note  that the “ground” elements must be at a 45 degrees angle. This way the antenna achieves the necessary electrical property of 50 Ohm impedance.

Our VHF Jungle Antenna build was inspired by these sources:

And here is a nice write-up on the BrushBeater blog.

Update 31/7/2016: I have just found another way to build this antenna. Check it at the “One more DIY Groundplane Field Antenna version” post.

End of part 1.

In part 2, I will cover the Dipole, the J-Pole and the Yagi Antennas.

So, If you liked what you read, please help us grow by sharing this post.

 

Tech Note 1: Different antennas radiate differently. So it is wise to suit the resulting pattern to the occasion. A Quarter-Wave Groundplane has a spherical pattern. That suits nice in uneven terrain. In a J-pole antenna the pattern is squashed into a donut and that gives some more range. And a Yagi antenna further draws the “dough” into a forward pointing lobe, giving directive characteristics.

Tech Note 2: If you choose to make your own antenna you are about to enter a new world, which –in the start- will appear more an alchemy than a science. Further down the road there is an Antenna Theory Basics article for this blog. But if you are to get an SWR-meter now and start making antennas you should at least read the Dipoles and Quarter Wave Myths paper and browse this Antenna Elmer site for simple antenna designs.

 

 

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2 thoughts on “Basic Antennas for VHF-UHF Field Communications part 1

  1. Thanks for great overview of easy but effective antennas. I tell newbies that they can make their little 2.5 watt handheld radio sound like a whole lot more if they just get a decent antenna. There are even tuned rubber duck antennas that deliver surprising performance. Whenever I buy a new handheld, the first thing I do is toss the stock antenna and get something else.

    Like

  2. Indeed! And they should at least try making one, even if they have to ask someone else to measure it.

    BTW, notice to all readrs: I updated/resized the pics and moved the text around a bit.

    Like

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