To receive all the frequencies you hear through this website, I built two identical antennas from plans I found on the internet. Both antennas are mounted in the attic of my house, and are attached to a horizontal section of roofing support. The antennas I built are known as quarter wave antennas. The quarter wave antenna is a simple design and can be constructed (or tuned) to receive whatever frequency range you are after.

There is a relationship between frequency and the wavelength, so the physical size of the antenna is a function of the frequency range you are aiming for. To get the wavelength of any frequency there is a simple formula. 300 divided by the frequency in MHz .

A vertical quarter wave length of wire, or metal rod by itself will not perform that well, and is really only half of the antenna. We need to add the other half of the antenna, which is known as 'the ground plane'. The easiest way to do this is to add similar length radials to the vertical quarter wave. They are not electrically connected to the quarter wave, and if we bend them down at a 45 degree angle, the impedance of the antenna ends up around 50 ohms which is what the majority of communication devices perform best with, and is certainly what is required for radio scanners.

Construction of a quarter wave antenna is quite simple, and in the design that follows, the cost is very low. Some wire, coaxial cable and a couple of plugs. Any electronics or hobby store should have all the parts you need. In the Kitchener Waterloo area Orion Electronics is as good, and as reasonably priced as anyone.

Parts required:

• Solid wire - I use straightened out coat hangers for one antenna, and some similar thickness metal rods my wife said she bought at a hobby store for some reason. Any metal rod that holds it's shape will suffice.

• One SO239 plug

• Coaxial cable

• Two PL259 plugs (or whatever plug you want) to suit the coaxial cable you will be using

• 4 small bolts (small enough to fit in the holes on the corners) and matching nuts (depends on the method – see below)

Theory:

For the Waterloo Control Tower frequency of 126.0 MHz you apply the formula of 300 divided by 126.0, and come up with 2.38 meters. Since we are constructing a quarter wave antenna, we divide the calculated wavelength by 4. In this case 2.38 meters divided by 4.  Therefore the length required for each metal radial on a quarter wave antenna tuned for 126.0 MHz is 2.38 divided by 4, which equals .60 meters, or 60 centimeters (23.6 inches)

Construction:

Before you cut your lengths of rods for the four radials, you need to decide how you will fasten them to the SO239 socket. There are two ways to do this – one is to solder them directly to the corners of the socket (where the holes are), and the second is to use a small bolt to fasten it to the socket. I used a combination of the two (bolts and solder).  If you construct this antenna for a lower frequency, the radial will be longer of course, and the bolt method may help with portability, but either method works well.

Note small loop at end for bolting radial to socket

Five lengths of wire (one quarter wave in length) need to be cut. In this example they are each 60 cm long. If using the bolt method to secure the radials, a small loop needs to be bent at the end of four of these rods to allow the bolt go through and this is part of the 60 cm length. The fifth piece of rod does not have a loop in it for either method. If soldering the radials directly to the socket, all 5 lengths are the same length and do not have a loop in them. The length without the loop is soldered onto the socket of the SO239 plug (on the opposite side to the socket where the PL259 is screwed in. Metal coat hangers from the drycleaners are a good fit and allow a sufficient gap for solder to flow into the hole, creating a good electrical connection on the SO239 plug.

Socket with the straight wire soldered in.