Two-way radios can operate on many different frequencies, and these frequencies are assigned differently in different countries. Typically channelized operations are used, so that operators need not tune equipment to a particular frequency but instead can use one or more pre-selected frequencies, easily chosen by a dial, a pushbutton or other means. For example, in the United States, there is a block of 5 channels (pre-selected radio frequencies) are allocated to the Multiple Use Radio System. A different block of 22 channels are assigned, collectively, to the General Mobile Radio Service and Family Radio Service. The citizen's band radio service (""CB"") has 40 channels.
In an analog, conventional system, (the simplest type of system) a frequency or channel serves as a physical medium or link carrying communicated information. The performance of a radio system is partly dependent on the characteristics of frequency band used. The selection of a frequency for a two-way radio system is affected, in part, by:
government licensing and regulations.
local congestion or availability of frequencies.
terrain, since radio signals travel differently in forests and urban viewsheds.
the presence of noise, interference, or intermodulation.
sky wave interference below 50–60 MHz and tropospheric bending at VHF.
in the US, some frequencies require approval of a frequency coordination committee. [cited from wiki]
You may think that “I can make phone calls instead of using walkie talkies”.
But some functions of walkie talkies cannot be replaced by cell phones. Firstly, they do not need base stations. They can still function well in places where there are no network signals. You can make instant communications without expenses incurred. Secondly, you can make one-to-many calls via walkie talkie, similar to group chat. However, most phone calls are one-to-one.
Car radios need to be installed on cars. Their power supply is from the car battery, so you’d better keep the car in the “Start” status. Otherwise, your car radios will not be powered on. Generally, the power of car radios can be maintained at about 25-50W. With high-frequency antennas, the communication distance can be maintained at about 30 kms.
Which factors can effect the signals?
The priority is Height > Location > Power. The most important factor is height. The higher, the more remote signals can be transferred. If you can’t find a place high enough, find a place where there is no interference. If even you cannot find a good place, you’d better choose a high-power walkie talkie.