Work around CB radio for enough time and someone is bound to ask you which model will throw a signal out furthest but there isn’t a straight forward answer to this question because much more is needed to run a successful CB radio setup than the rig itself.
If you take the time to get a CB setup together its only natural you want it working at its best so in this article we are going to look at how to change your CB station to increase the “reach” of your signal along with what makes global communication possible at CB’s 27MHz frequency allocation.
Adding Extra Juice
Increasing the power output of any RF transmitter will result in better coverage and CB radio is no different. As a rule of thumb CB’s are traditionally limited to 4 Watts which is keeping in line with the short range community communication role it was originally designed for.
This limit however is often exceed either illegally or by a relaxing of laws governing CB radio in certain parts of the world and its not uncommon for CB’s to have a power output exceeding 100 Watts. The design of a standard mobile type CB radio doesn’t leave the space or the power delivery structure to have large amplifiers placed inside so this increase in power is produced by fitting an external RF linear amplifier that fits in between CB and antenna.
As most stock CB antennas and coaxial cable are designed for use at the low 4 Watt RF output generated by a basic CB transmitter checking the ratings of both is advisable as pushing a few hundreds Watts through a system not made to handle that sort of power could be a costly mistake with the possibility of not only damaging the antenna but also frying the RF output section of the CB Radio Transmitter.
Antenna Location and Height
The term “line of sight” refers to how far a radio signal can travel until it gets blocked by an impassible object with the most effective signal killer being the earth itself. All things being equal at both receiving/transmitting stations with completely flat ground between the two there is a distance of 18 miles before the natural curvature of the earth gets in the way.
By increasing the height of either stations antenna the distance increases because the height lets the signals overcome the natural curvature of the earth. Most utility transmissions are on frequencies that suffer from the line of sight problem and walking around any mountain or high point in cities and you’ll see large towers bristling with antennas for everything from cell phones to local taxi companies, all attempting to give the best range possible for transmitted signals.
Not all signals encounter this problem with transmissions in the extreme lower section of the radio spectrum producing a ground wave that uses the earth to extend their range by following it around the horizon. Ground waves will travel further with more power output but when working with a strict line of sight transmission no amount of extra juice will conquer the curvature of the earth.
More Efficient Modulation Modes
Some modes of modulation perform poorly over long distances with FM being one of the worse for reliable communications. So called compressed modes such as SSB (Single Sideband) are easier to resolved with a better signal to noise ratio and its not by chance this is the primary mode used for everything from aircraft to radio amateurs attempting worldwide communications.
A sideband transceiver first creates a full AM (Amplitude Modulation) signal then cuts it in half before transmission to produce the SSB signal, the station receiving the SSB signal simply recreates the full AM waveform again by duplicating the half it already has.
Understanding CB Radio Global Communications
The most common effect that gives the CB signal that special ability to travel much further than line of sight is whats known as “skip” and under the right conditions this effect can make signals at 27 MHz go around the globe.
When Radiated power leaving your antenna hits the ionosphere at the right angle its refraction back to earth at a much greater distance than any line of sight signal could ever travel. This is the same method used by satellites to send high quality radio signals around the world but they offer a more stable method of doing so as conditions in the ionosphere are unpredictable and change rapidly.
The strength and thickness of the ionosphere gives any radio signal hitting it a better chance of being bounced back to earth. The condition of this layer of ionized particles is governed by the output of the sun with its health directly related to the level of ultraviolet radiation emissions striking it which peak every 11 years as the “solar cycle” reaches its maximum.
Extra RF output power can help when trying to contact other countries using skip but this isn’t always the case. During the summer months when the sunspot is at or near its maximum local CB radio signals can easily be swamped by long distance low power transmissions, in fact there is a branch of amateur radio called QRP where the goal is to achieve the best distance two way communication using the least power possible.
Directional antennas are an efficient way of enhancing the skip transmission method by giving your signal the right elevation to improve the chance of hitting the ionosphere at the correct angle to refract as much RF power back to earth. While beam antennas are small powerful units in the VHF/UHF frequency range those constructed for CB radio are large heavy affairs that need towers and rotators to enjoy their full potential.
Only transmissions at lower frequencies can make use of this wonderful quirk of nature with signals at VHF (Very High Frequency) and above just passing straight through the ionosphere and out into space.
Over to You!
All the information above not only answers the question about the range of CB radio transmissions but is a checklist for making your setup that much better. Even a slight change in power, transmission mode or antenna location will improve the range or your CB radio if done correctly.