Antenna Elements

University of Alberta observatory domes


"Thank you so much for visiting our class on Friday! The kids loved it...they thought it was pretty cool to meet a "real" Astronomer! Thanks again, Janine"

How to Make the Antenna Elements


There is a variety of material that can be used to make the antenna elements. Some work better than others. There are a few characteristics that are useful to know about:

made of metal, preferably copper or copper coated material. Aluminum can also be used.
they can be made of wire or tubing.
they must be straight and remain straight when mounted. Tubing works well for remaining straight. Steel brace wire used for fences such as chain link or page wire fences is pretty strong and while it flexes a bit can still be used. The drawback is that it doesn't conduct electromagnetic energy as well as copper or aluminum. Nevertheless, we have used brace wire and it works even though it is not ideal.

Each material and its characteristics are described below:

Material Stiffness Conductivity Cost
Copper house wire 12 or 14 gauge. Comes in rolls. Will need extra support Good Low
Copper coated steel welding rod. Good but has to be soldered together to get enough length Good Medium
Copper tubing. Comes in rolls. Good. Will need to be straightened. Good High
Aluminum tubing. Difficult to find. Good. Good High
Steel brace wire. Can support itself but a little floppy. Poor but works. Low


Note that the elements for the Yagi antenna each have a length specification that can be found on the Dimension Table for the frequency you will be observing at. Whatever material you use needs to be cut to the correct length.

If you are using copper wire, it will need to be rigid enough to support its weight over the long spans that the FM frequency band requires. The adjusting block design described in the 6 Element Yagi page can be used to hold a piece of thin, flat wood as a stiffener for the copper wire. The wire simply needs to be attached to the top of the long flat wooden slat (such as wood molding stained or treated for exterior use) that you can get at building supply stores.

To cut the elements to length, you will need wire cutters or a hack saw depending on the material. Be careful to use heavy wire cutters if you are using steel brace wire as it is hard to cut. Tubing can be cut with a hack saw.

Since it's easy to mix the elements up after they have been cut to length, be sure to label each element, D1, Reflector, Driven Element, etc. so you'll know where to attach it when it comes time to assemble the antenna.

Making the Driven Element

The Driven Element is, in a sense, an antenna within an antenna. The Reflectors and Directors add extra tuning and help to focus the radio waves to the Driven Element. Our antenna design uses what is called a Folded Dipole. Use twin lead or ladder line cable available at electronic supply stores or at many hardware stores to make it.

See the Dimension Table to determine the length of the Driven Element. Measure and cut a piece of twin lead cable to this length. Strip 12 to 15 mm of the insulation from the 2 wires at each end of the dipole. Twist the wires together and solder them. 

Find the centre point of the twin lead. Cut one of the wires at the centre point and pull the wire out in each direction so you have enough room to strip the insulation back from the cut ends about 12 to 15 mm. Then take the 300 to 75 ohm matching transformer, wrap each of the now bare wires around the two leads, one to each lead, and solder them together. Wrap the leads with electrical tape to prevent them from contacting each other causing a short circuit (there is no danger of electrical shock here).

Twin lead is not stiff enough to hold its shape and so the complete dipole must be attached to some kind of stiff backing material such as wood. Use a staple gun to staple the twin lead or ladder line to the backing material being careful not to drive the staple into the wire.

Once the antenna is completed and you are ready to begin observing it must be attached to a 75 ohm exterior rated coaxial cable connected from the matching transformer to your receiver.

Copyright 1999-2015 by Sky Scan, Edmonton, Alberta, Canada. 

We gratefully acknowledge the financial support of the 

Edmonton Centre of the Royal Astronomical Society of Canada, Department of Physics (University of Alberta)

and the

Natural Sciences and Engineering Research Council of Canada

Home    Site Map   Search   FAQ    Links   About Sky Scan   Webmaster  Contact Us