# Antennas for 15 Meters

## Antennas for 15 Meters

### Antenna: 15 meters, Range: 21 to 21.45 MHz

Good 15 meters antennas are easy to build with nothing more than readily available materials. Since 15 meters covers the frequency range of 21 to 21.45 MHz you can use a few algebraic formulas to compute antenna sizes.

In the case of antennas for 15 meters you can see the antenna size begin to increase but not too large. A survivalist can make good use of a dipole antennas for 15 meters. A dipole is nothing more than taking the whole length of wire and cutting it in half. Each piece is separated with the shield of the coaxial cable connected to one wire end while the center conductor of the coax is connected to the other. Dipole antennas for 15 meters are easy to deploy as you can throw a couple of ropes up into trees or other structures and pull the antenna up and out of the way.

This formula: 234/f can be explained by dividing 234 by the desired frequency in megahertz which will give you the length, in feet, of a 1/4 wave antenna. This formula isn’t exact in that it assumes the radiating element is infinitely small. What this means is if the radiating element was one inch in diameter then the resonant length of the antenna would be a little shorter than the calculated one given by the formula gives you.

Using the formula above you will soon see that an antenna for 15 meters is approximately 11 feet 15/32 inches in length. This antenna measurement can be used for either a vertical antenna for 15 meters or a horizontal antenna for 15 meters.

15 meters is a great band and could be pressed into service for either day or night time use depending upon the current sunspot cycle.

# Beam Antennas

## Beam Antennas

Beam Antennas.
We have all seen at least one of these antennas around. They are usually on top of a tower or at the very least on the roof of a tall building. Beam antennas need to be a good distance up in the air in order for them to work adequately. A good height for beam antennas is generally 40 feet high but you will see them on top of towers over 100 feet tall. Many times on these larger towers you will see more than one of these beam antennas with each antenna dedicated to a certain frequency. One point of interest with beam antennas is that the smaller the antenna the higher the frequency it is used on.

The use of beam antennas in survival environments is not unheard of but the logistics of the tower, the rotator, and the antenna itself would likely be enough to prevent their use in most survivalist operations. In case you’re wondering, the rotator mentioned earlier is to turn the antenna in the direction of the station you wish to communicate with. By their design a beam antenna’s most powerful signal is heard from the front of it and the best way to block an offending signal is to turn a beam so the side or back of the beam is directed at the offender.

Beam antennas are not all created the same, some are made from aluminum tubing and are called yagi antennas. Another design for beams is that of a quad antenna. This antenna consists a 2 large arms crisscrossed and then a wire connects to the end of each of the arms. This antenna has an excellent reputation in the amateur radio community but it is quite a bit larger than a yagi antenna.

So before you contemplate the use of a beam antenna at your compound or even at your base station you need to total up the costs as well as the work involved in setting up a beam antenna. If you are working portable then you likely will not consider a beam antenna.