Three Important Things to Consider Before Building a Ham Radio or CB Antenna
Building communications antennas can be fun and exciting especially for the new antenna builder that is eager to get started. But no matter what type of antenna you are building there are some important things to consider before getting started. Here are a few tips to help put you on the path to success with your antenna projects.
Number One: Purpose
The first consideration is, "How do you plan to use your antenna?" Before building any communications antenna you need to know what purpose the antenna is intended to be used for. There are different applications for the use of antennas. Some antennas are for short range communications while other antennas are specifically designed for long range or satellite communications.
Vertical antennas, such as mobile antennas and base station ground plane antennas, are basically for short range communications. When such an antenna is mounted in a vertical position we refer to it has being vertically polarized. A vertical antenna, or a vertically polarized antenna, sends it's signal out along the earth's surface. This type of radio wave propagation is called, "ground wave." Although mostly for base to mobile communications a vertical antenna is also capable of working long distance communications. A ground plane antenna has a low angle of take off and sends it's signal out towards the horizon before bouncing off the ionosphere. A vertical antenna elevated on a mast will produce both a low and high angle of take off which in a way also increases gain.
Horizontal antennas such as dipoles, inverted V antennas and other horizontally polarized antennas are for working "sky wave" propagation. These antennas are for receiving signals that are coming down from the ionosphere and for transmitting signals back into the ionosphere. Bouncing radio waves off the earth's ionosphere is how we communicate long distances. Charged ions in the ionosphere and favorable band conditions will allow even a 5 watt transceiver to receive and transmit half way around the globe. Horizontal antennas are not meant for close range communications. So if you build a horizontal dipole or an inverted V antenna for the CB band it will do a great job working stations half way across the country but it will not work very well for local communications.
Number Two: Cost
The next thing to consider is the cost of your antenna project. Some antennas are less expensive to build rather than purchase but in some cases it is less expensive to buy the kit! Antennas made of PVC pipe and wire cost very little to make while antennas made of aluminum tubing become much more expensive to construct.
In some cases it is less expensive to buy an antenna rather than buy all the parts to build it yourself. A small HF 3 element yagi antenna is often less expensive purchased as a kit than it is to buy all the parts separately. If you need to buy all new parts for a CB antenna then even a nicer vertical dipole made of aluminum tubing and mounted on a boom may cost more to make than a ready-to-install fiberglass half-wave antenna that performs about the same.
On the other hand, many of us do enjoy building our own antennas and so some of us would not mind paying a little extra for the pleasure of building it ourselves. The cost is really up to you.
Number Three: Resources
Now consider your resources. What do you have on hand to use for materials and how are you going to install the antenna? Resources are what materials you have on hand to work with and the space, area or way to mount the antenna. The type of antenna that you build may be limited by the way that you intend to mount your antenna. Not everyone has a lot of space to work with and often times space and height is the problem especially when it comes to larger HF antennas.
Vertical antennas can be mounted on a mast or mounted on the ground. For transmitting and receiving signals by means of ground wave propagation and "line of sight" vertical antennas are best mounted as high as possible on a mast or tower. HF vertical antennas mounted on the ground perform better as a long distance antenna.
Horizontal antennas such as horizontal dipole antennas require height in order to properly radiate a signal. These types of antennas will not work correctly if mounted too close to the ground. The required height depends on the wave length. Horizontally polarized antennas made for higher VHF/UHF frequencies do not require as much height as do larger HF antennas.