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But First The History of CB radio.....

It is a form of shot-distance communication between individuals on the 27-Mhz or 11meter band frequency, on selection of 40 channels. But the channels and the law of using a CB radio variate from country to country. In many country's CB operation dose not require a license, unlike Amateur Radio where you have to pass the test to be able to operate . It may be use fore business or personal communications, like many other two-way radio services. CB channels are shared with many other users and it can be fun to talk or just listen to them.

Old Vacuum Tube CB Radio

 CB radio or CB Radio service originated in the United States as one of several personal radio services regulated by the Federal Communications Commission (FCC). These services began in 1945 to permit citizens a radio band for personal communication fore family and business communications and radio-controlled model airplanes (actually some of today's toys steal use a 27-Mhz transmitters an receivers to control RC vehicles). 

Old Vacuum Tube CB Radio

                                  

In 1948, the original CB Radios were designed for operation on the 460–470 Megacycle UHF band. There were two classes of CB radio: A and B. Class B radios had simpler technical requirements, and were limited to a smaller frequency range. Al Gross established the Citizens' Radio Corporation during the late 1940s to manufacture Class B handhelds for the general public.

On September 11, 1958 the Class D CB service was created on 27 MHz, and this band became what is popularly known today as CB. Back in the day's there were only 23 channels at the time; the first 22 were taken from the former Amateur Radio Service 11-meter band, and channel 23 was shared with radio-controlled devices.Some hobbyists continue to use the designation "11 meters" to refer to the Citizens' Band and adjoining frequencies. Part 95 of the Code of Federal Regulations regulates the Class D CB service, on the 27 MHz band, since the 1970s and continuing today...

1970s CB Radio

During the 1960s, the service was popular among small businesses truck drivers and radio hobbyists. By the late 1960s advances in solid-state electronics allowed the weight, size, and cost of the radios to fall, giving the public access to a communications medium previously only available to specialists.CB clubs were formed; a CB slang, language evolved alongside 10-codes, similar to those used in emergency services.

CB has lost much of its original appeal due to development of mobile phones, the internet and the Family Radio Service. Changing radio propagation for long-distance communications due to the 11-year sunspot cycle is a factor at these frequencies. In addition, CB may have become a victim of its own popularity; with millions of users on a finite number of frequencies during the mid-to-late 1970s and early 1980s, channels often were noisy and communication difficult. This caused a waning of interest among hobbyists.The advantages of fewer users sharing a frequency, greater authorized output power, clarity of FM transmission, lack of interference by distant stations due to "skip" propagation, and consistent communications made the VHF (Very High Frequency) radio an attractive alternative to the overcrowded CB channels.

Channel 9 is restricted by the FCC to only emergency communications and roadside assistance. Most highway travelers monitor channel 19. CB radio is still used by truck drivers, and remains an effective means of obtaining information about road construction, accidents and police radar traps.

All frequencies in the HF spectrum (3–30 MHz) can be refracted by charged ions in the ionosphere. Refracting signals off the ionosphere is called sky-wave propagation, and the operator is said to be "shooting skip". CB operators have communicated across thousands of miles and sometimes around the world. Even low-power 27 MHz signals can sometimes propagate over long distances.
The ability of the ionosphere to bounce signals back to earth is caused by solar radiation, and the amount of ionization possible is related to the 11-year sunspot cycle. In times of high sunspot activity, the band can remain open to much of the world for long periods of time. During low sunspot activity it may be impossible to use skywave at all, except during periods of sporadic electron propagation (from late spring through mid-summer). Skip contributes to noise on CB frequencies. In the United States, it is illegal to engage in (or attempt to engage in) CB communications with any station more than 250 km (160 mi) from an operator's location. This restriction exists to keep CB as a local (line-of-sight) radio service; however, in the United States the restriction is widely ignored. The legality of shooting skip is not an issue in most other countries.