Antennas
How to make a 1/2 Wave Dipole
Needed:
- Wire (speaker wire will work just fine)
- Solder gun & Solder
- Measuring tape
- Coax
First, you'll have to decide what frequency you're making your antenna for. For amateur radio usage, you'll usually pick a frequency in the middle of the band you're using (i.e. 146MHz for the 144-148MHz 2M band). In this example however, we'll be making our dipole for broadcast FM. Chances are, the antenna for your home stereo radio was just made for the middle of the broadcast FM (88-108MHz FM in North America). If my favourite station is near the end of that range, the reception will be less than optimal. I'll use 106.9MHz as my example favourite radio station.
A dipole is cut to length according to the formula l=468/f(Mhz). Where l is the length in feet and f is the center frequency. In metric that is l=143/f(Mhz) where l is the length in meters. We'll use Imperial, as the majority of the wiki readers are American, as of writing.
With that in mind:
468 / 106.9 = 4.38
As this is a 1/2 wave dipole, each side will be 1/4 of the length:
4.38 / 4 = 1.1
So each side of the dipole will be 1.1 feet long. Cut two pieces of wire a little longer than 1.1 feet, as you'll be soldering one end, and attaching the other end to a loop as well. With one end of your coax, you'll want the center of the coax to be soldered to one wire, and the shielding of the coax soldered to the other matching piece of wire. You will want to make sure these two never touch, they need to be going in 180 degree directions from eachother. The easiest way to do this is often to place an insulator between the two. In my case, I used a 2" scrap piece of plastic. Once you've verified the two sides are not touching, you can hook the other end of the coax up to your radio. Keep in mind the radiating pattern is 180 degree perpendicular to the wires, so it is directional. Once you've got your dipole pointed towards the tower of the broadcasting station (Getting its location, and then using a compass is a simple way), make sure it's well secured. You've now built an antenna optimized for your favourite radio station.
This same process can also be used for television for example, useful for those without cable tv or satellite, and only currently using "bunny ears". If you have a favourite t.v. station, you can optmize your antenna for your favourite channel. Keep in mind that there is a frequency for both audio and video. North American Televsion Frequencies
