When designing a radio system, the antenna is a crucial component. You want to maximize the RF energy from your radio to be radiated from your antenna. The antennas are specified with some of the following considerations:
- Maximum Power – The amount of RF that they can typically handle without failing. An antenna that is rated at 100 watts will work effectively at that power. If we run it at 150 watts our risk of shortening the life of the antenna increases.
- Frequency – All antennas are rated in frequency. This is key to insure our TUNED antenna circuit matches our frequency. We do not want to use a 450Mhz antenna on a 150Mhz transmitter. Power transfer will be poor as the antenna is resonating on the wrong band.
- Gain – Each antenna has a gain figure. Whether in dBi or dBd, the value tells us that for a specific power input, the antenna will re-radiate that power at an effective higher level. For instance, if we input our 100 watts into the base of a 3dBd gain antenna, the corresponding effective power radiated will be about 200 watts.
- Beam width – Beam width usually corresponds to the gain of the antenna. A higher gain antenna will have a smaller beam width. This is the angle at which an antenna radiates. Picture an antenna stick that is 10 feet high. At the center of the antenna the radiation pattern goes up and down. The envelope of that pattern is the beam width. A unity gain antenna may have a 78 degree envelope where a 9dBd antenna may have a 15 degree envelope. This may come into play where extending your coverage farther out is required.
- Wind Load – Many of the VHF antennas are up to 20 feet in length. Imagine installing many of these on a tower. They act like a sail in the wind and create a drag on the tower structure itself. Thus too many antennas can create stress which can fail a tower.
- Weight – Again similar to wind load, the weight of the antenna will create stress on a structure which can become a safety concern if exceeded. Many towers are rated with specific wind and weight loads.
These are just a few of the considerations. In addition you need to watch what you’re mounting the antenna to. Many antenna structures can create a dome effect or null zone directly below the structure. Picture a water tower. One thousand feet away you can see the antenna, yet directly underneath of the water tower you are shielded from it. This dome effect creates a dead zone around the structure.
All of the components of antenna theory are key to properly designing a system. It helps you achieve your Effective Radiated Power (ERP) on the IC License and it insures you maximize your coverage through proper power transfer. Bigger is not always better in this case. Coverage modeling helps to reveal the factors mentioned above. In addition, propagation is a science used to analyze the strength of the signal received and transmitted by the antenna. If any of this has you confused, the engineers at Westcan Advanced Communications Solutions have the capability to complete a potential review and propagation analysis for you and they can walk you through it step by step. This keeps the guesswork out of radio system coverage.
Now that I’ve laid out the most important factors to consider I hope you’ll put your systems to the test. The important thing to take away here is that maximizing your investment is the key to good radio coverage. If you have a system that’s already been built and you’re experiencing dead spots, your next lesson is to learn how to boost indoor coverage, and Westcan Advanced Comminations Solutions have a solution for you. If you’re interested in discussing these points, or any other questions you may have, feel free to contact me directly through the form below.