Two-Way Radio
Unlike a broadcast receiver which only receives broadcasts for listening, two-way radios can transmit information in addition to receiving it. The transmitter is commonly activated by pushing a button and speaking into a microphone. Perhaps the most common and well-known two-way radios are known as walkie-talkies. But two-way radios are available in stationary models as well as mobile varieties. Cell phones are another good example of a two-way radio that transmits and receives simultaneously. Cellular phones use two different radio frequencies to carry the both sides of a conversation. History of Two-Way Radios
Two-way telegraphs were used to transmit messages across the Atlantic Ocean in the early 1900s. Receivers and transmitters were installed at the same fixed location to allow the wireless exchange of information. Military and commercial ships carried transmitters & receivers by 1912 allowing almost real-time communication with ships at sea. Smaller, more powerful, and more easily operated equipment became available as technology advanced and could be installed on smaller vehicles. The use of two-way radios in airplanes eliminated the need for the crew to drop messages to troops or land in order to make a personal report. Information could be relayed almost instantly as scouts made observations from the air. Air & ground troops used two-way radios extensively during Word War II. The first recorded use of two-way radios in law enforcement was in Bayonne, New Jersey, in 1933 when the system installed at police headquarters was able to communicate with radio transceivers installed in police cars. As a result, police response to emergencies improved dramatically. Since all signals used the same frequency, the earliest two-way radios allowed only one station at a time to transmit. The others could only listen and wait their turn to transmit. The "simplex" mode as it was called required communication protocols as a way all stations could cooperate and use the single frequency without obscuring each other's transmissions. "Full duplex" mode which allowed simultaneous transmission and reception became available when the use of different frequencies for transmission and reception was adopted. Using a two-way radio today is almost as simple as using a telephone but it wasn't always that easy. Voice communication was not available in the first two-way radios. Morse code was used which usually required a full-time operator who was trained in the use and translation of Morse code. After voice transmission was possible and operators were no longer needed, the use of two-way radios grew rapidly. Two-way radios are so inexpensive and easy to operate today that the technology has a wide range of practical uses ranging from personal to commercial to law enforcement and military operations. Types of Two-Way Radios As you might imagine there is a vast array of two-way radio systems available including conventional, trunked, and scanners. |
