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A CB radio amplifier is a solid-state or transistor device that can double or triple amplitude and increase the wave input/output ratio, called gain. Operating in ranges from about 3 to 30 MHz, and up to 18 gigahertz (GHz), types of amplifiers vary, typically in the amount of voltage they apply to the control grid. They can differ by classes, band usage, power, and noise levels. Determining the best choice for your needs depends on careful understanding of the conditions of your most typical transmission areas, the type of radio and antenna employed, and clear understanding of legal and social limits for your use of public communications bands.
Citizens Band two-way radios operate in the high frequency (HF) band of the electromagnetic (EM) spectrum, at about 27 megahertz (MHz), between amplitude modulation (AM) and frequency modulation (FM) frequencies. The output power of these radios is usually limited by law. In the US, the Federal Communications Commission (FCC) limits it to 4 watts and 150 miles (about 241 km), though these radios typically service a short range area of about 9 miles (14km).
Power supply is an important factor when considering a CB radio amplifier. One limiting factor of power output is total input power, which should be greater than expected output. An increased, constant output level depends on input wattage, power source voltage, and amps produced. For example, a 100-watt amplifier could generate 14 amps times a 12-volt DC power supply, making an input of 168 watts for an output of 100 watts for antenna transmission. This input/output ratio is referred to as the amplifier's efficiency.
Amplifiers, like antennas, are called transmitter or receiver types; this means they differ as transmitter radio frequency (RF) amplifiers, and receiver RF amplifiers, also known as pre-amps. Numerous models vary in band, power, and noise level. A wide range of legally sold but not necessarily legally employed CB radio amplifier products can output noise levels from 0.5 to 50 decibels. Three broad product categories are variable gain, broadband, and low noise types.
Variable gain amps modulate incoming signals along the band for analog-to-digital (A/D) conversion. Broadband amps reproduce signals throughout the pass band without significant loss. Low noise amplifiers (LNA) impart a steady gain over given frequencies above circuit noise in order to improve sensitivity and range. Power amplifiers deliver maximum power rather than voltage gain; these linear amplifier types deliver a proportionally increased output rate for extended range in field use. With linear, think distance.
Other aspects to bear in mind when selecting a CB radio amplifier include its dynamic range, responsiveness to the entire band, impedance, and susceptibility to electromagnetic interference (EMI). A spectrum-analyzing device may also be needed to optimize the driving signal and eliminate unwanted sideband signals. Modulation must be 100% or less; overmodulation caused by too much power creates self-defeating output interference. Signal leakage not only disrupts reception in CB bands but also neighboring cable television and ham bands, and may alert the authorities to any illegal use of equipment. Consider your standing wave ratio (SWR) readings, length of coax cable, and the one thing your system should already have before you think about a CB radio amplifier: a good, well-positioned antenna or two.