Choosing the right antenna for your UHF base station
Any self-respecting CB radio enthusiast generally has a base station installed at their house. Whilst the purpose and types of stations vary wildly, most users leverage the additional space and mounting infrastructure available in a fixed location to install a more performant antenna system to increase their range, as well as their ability to “get into” their local repeaters.
Choosing the right antenna for your UHF CB base station can seem confusing at first – there are a multitude of different options available. The antenna you choose will have an equal if not greater impact on the performance of your installation than the radio itself. With this in mind, selecting the right antenna is imperitive to ensuring your UHF CB performs as expected.
Types of Antennas
Different antennas have different properties such as size, shape, gain and radiation pattern. It is these final two properties which affect the performance of the antenna.
Omnidirectional antennas, as you may have guessed from their name, radiate in all directions. This makes them suitable for general purpose communications in the local area. There are two main types of omnidirectional antennas: colinear antennas (colloquially called “sticks”), which are commonly used for vehicular communications and dipoles, which are often used for high performance commercial base stations and UHF repeaters.
By far the most common type of onmnidirectional antenna for base stations is the stick antenna – they are cheap, ubiquitous and often easy to mount to your existing TV antenna pole. This makes them a popular choice for beginner users, or users who don’t want to invest large amounts of money into their station.
If you do select a stick antenna, keep in mind that these require a “ground plane” – usually, this ground plane is provided by the body of the vehicle on which the stick is installed, but this is not the case when you are installing your antenna on the roof of your house. If you have a tin roof, a ground plane can easily be achieved by electrically bonding the metal base of the antenna to your roof. If you have a ceramic, asbestos or other non-metallic roof, you may need to run a separate ground cable – with this in mind, it may be more practical to use a dipole antenna.
Dipoles are a popular choice for users who require better performance than is afforded by traditional colinear antennas or users who do not have an adequete ground plane. Dipoles are generally more expensive than stick antennas, as they are intended for use in commercial environments. They often have more complex mounting requirements also, which may require additional infrastructure to install.
For more information choosing a stick antenna, check out our article “Choosing the right antenna for your mobile UHF CB station”.
By far the most common and effective directional UHF antenna is the Yagi antenna, colloquially called a “beam”. The Yagi antenna is an incredibly directional, very high gain antenna that is perfect for accessing a single CB repeater. Radio enthusiasts who regularly use a single repeater will often have one or more yagi antennas which are pointed (aligned) directly at the antenna of the repeater station in order to achieve the best possible signal into that particular repeater.
Multiple yagis can be joined together to increase gain using a method called co-phasing. Whilst this is an effective strategy to improve performance above and beyond what can be achieved with a single yagi antenna, it is often not practical or achievable for users who are unfamiliar with RF design principals, as antenna placement is absolutely critical to avoid self-interference and intermodulation issues. Achieving peak performance using a co-phased array also requires expensive equipment (such as an antenna/vector network analyser) which is not available to the vast predominance of users.
Connecting Your Antenna
Regardless of which type of antenna you select, you will obviously need to connect it to your radio. This is achieved by using a coaxial cable. The type of cable you select also has a substantial impact on the performance of your installation.
You may be tempted to try and use cheap and readily available 75-Ohm coaxial cable such as RG6/RG6Q. Unfortunately, the impedance of this cable makes it incompatible with any two-way radio system. Instead, you must use 50-Ohm coax such as RG58, RG174U or LMR400.
All coaxial cable is “lossy”, which means that a certain amount of RF energy is lost along the length of the cable. The more loss, the weaker your signal will be before it reaches your antenna. Loss is a product of the length of the cable, as well as the type of cable that you use.
Generally, you will want to place your radio as close to the antenna as practically possible to minimise the amount of loss from cabling. Lossier cable is thinner and less expensive, whilst less lossy cable is thicker and more expensive. Which cable you use will be a trade-off between the amount of loss you are willing to accept and the amount of money you’re willing to spend.