2013年1月6日星期日

About 2 Way Radios

Types
There are many different types of 2 way radios. Each family has a variety of sub-types and specific radio models. Conventional two-way radios operate on a fixed RF channel, with the proper channel being chosen by the user. Trunked two-way radio systems automatically pick up the physical frequency channel.
Simplex two-way radios use a single channel for receiving and transmission. Aircraft and Marine systems are usually simplex radios. Duplex two-way radios transmit and receive on two different channels and typically require a repeater or base box to function.
Push-to-talk two-way radios are usually found on modern cell phones and walkie-talkies. They feature a button that, when pushed in or in one direction, allows transmission. When the button is not pushed or pushed in an opposite direction, messages may be received. Analog, digital and hybrid are other types of two-way radios.
Frequencies
Two-way radios are capable of operating on many different radio frequencies. These frequencies are assigned by the country in which the radio is being used. Each country assigns frequencies based upon international agreements to different two-way services. In the United States, for example, there is an assigned block of 22 different channels. A channel is a shorthand term for a specific frequency.
Formats
Two-way radios are available in two primary formats–Ultra High Frequency (UHF) and Very High Frequency (VHF). A UHF station requires 3,000,000 watts to operate over a range of 60 miles, while a VHF station uses only 100,000 watts over 60 miles. Outdoor usage is best suited to VHF. If the radio will be used mostly indoors, UHF may be the best choice. Typically, the lower the frequency, the more effective it is for long range use.

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