Carrier Frequency bands

• The carrier waves frequencies for radio broadcasting are assigned by Federal Communications Commission (FCC)
• AM carrier frequency - 535 kHz to 1605 kHz
• FM carrier frequency - 87.5 MHz to 108 MHz

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How a two way radio system works

Basically, a radio communication system consists of a transmitter, a channel, and a receiver.

• In a transmitter,

The input sound signal is converted into equivalent electrical current / voltage by a transducer The transducer output is amplified by a chain of amplifiers (so that it can travel longer distance) The purpose of the transmit antenna is to efficiently transform the electrical signal into radiation energy

• In a receiver,

The receive antenna efficiently accepts the radiated energy and convert it to an electrical signal As the signal suffered attenuation during travel it requires further amplification The output transducer converts the electrical signal back into sound energy

A B

• Simplex – A can talk to B

Radio, T.V. broadcasting, CD/DVD ROM Simplest type, requires one transmitter and one receiver Types of Communication

• Duplex – A and B both can talk to each other simultaneously

Telephone, Telegraph, Complex, requires two transmitter and two receiver at both ends Needs two different channels for simultaneous transmission

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History of two way Radio

The first portable 2-way voice radio developed by Hings in 1937, the "Light Aircraft Emergency Set" was only 12 pounds, battery included, range approx. 130 Miles, painted yellow and water tight when the cover over the dials was locked on with two quick release latches on either side. Made buoyant for people near water in case the plane had to drop the radio into the water while still flying. Fold down antenna included in case. Capable of 2 frequencies, one for the company “Cominco” and the other for the “Canadian Army Signal Corps”. Could be carried while transmitting and receiving voice.

December 7, 1938; The 10PC20 Airplane Radio developed for Cominco pilots.Using the same technology for the Light Aircraft Emergency Set, made voice communication in small aircraft feasible of long transmission distances. This set was also capable of transmitting code and voice, as were most of the units Hings developed.

In Sep. 2003 US manufacturers released the first application allowing a GSM to act like a walky-talky. In Nov. 2003 Nokia, provided the first push-to-talk (PTT) GSM, the Nokia 5140, displayed at left. According to a poll made on Aug. 2003 in the U.S.A by Zelos Group 45 % of them declared wishing that their next GSM is equipped with the PTT functionality. The Push-to-talk comes thus in second position behind the picturing functionality.

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