New Electronic “Ear” Versatile Communications Aid
An “electronic ear”, deaf to all but a single electronic tone, or combination of tones, was recently described by Charles I., Rouault, General Electric communications expert, speaking before the annual meeting of the Institute of Radio Engineers. The device, Mr. Rouault said, has led to development of a new line of products which add privacy to mobile radio systems, and greatly speed pushbutton remote control operations.
Connected to a special switch, the sensitive listener is capable of turning on and off any kind of electrical apparatus, from radio receivers and transmitters to electric motors, which can in turn perform numerous functions.
The electronic tones, within the range of human hearing, are produced by a small electronic tone generator. They may be broadcast by radio or carried over telephone wires to any number of electronic “ears.” They are transmitted in about two-tenths of a second and travel at the speed of light.
The tone generator, which is entirely electronic and has no moving parts, is operated from a pushbutton console, having from one to 40 pushbuttons. These cause tones to be transmitted, with combinations punched out like an adding machine.
Any number of “ears” can be reached from a single console. Each is made to “hear” only one tone, or pair of tones. All others fall on a deaf “ear”. The 80 tones used are between 300 and 3000 cycles. Ultimate possibilities are that more than 500,000 “ears” could be reached from one desk-top console having 60 pushbuttons, according to Mr. Rouault.
The G-E engineer outlined several uses currently envisioned for the electronic tones. Three in the mobile radio field are called selective dispatching, duplex dispatching, and selective calling. A fourth lies in the broad field of remote control. Combinations of these are a great aid to civil defense communications.
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He described the mobile radio uses as three progressive degrees of privacy, from a “party-line” system through a “private-line” system.
As currently operated by numerous agencies like police and fire departments, and taxicab companies, all equipment in a mobile two-way radio system operate on a single frequency or pair of frequencies. Where two frequencies are used, one is for the dispatcher to call mobiles, and the other for mobiles to call the dispatcher.
This one frequency per system means that all persons in the system hear all calls made. No two persons can talk privately. Much strain and confusion is caused for drivers and passengers, who hear all calls, whether intended for them or not.
Use of the new tones and electronic “ears” can reduce this strain and confusion through a method called selective dispatching, Rouault said. For example, a taxicab company with 100 radioequipped cabs can be divided into ten groups. Electronic “ears” would be added to radio receivers in the 100 cabs. The “ears” in each group would “hear” a different tone, a total of ten tones. The dispatcher could then talk with an individual by pushing the button for his group. Only the ten drivers in that group would hear the dispatcher’s call, and when the called driver replied, the other nine receivers in the group would automatically drop out of the ensuing conversation.
This method carries the above one step further, by adding an electronic “ear” to the dispatcher’s receiver, and tone generators to the cab transmitters. This system permits a driver to call the dispatcher without being heard by any of the other drivers.
The final step, or “private-line” method of using the tones and “ears” is selective calling. For this method, the receivers in each of the 100 radio-cabs would have an electronic “ear” capable of hearing a different combination of tones. The dispatcher could therefore call any one individual driver privately, just as you dial a telephone number, the G-E engineer explained.
Selective calling would be most useful in radio systems having large numbers of mobile receivers, and where private conversations are necessary or desired. Any number of parties can be privately contacted by selective calling, from a few to more than 500,000.
In all these methods for increasing privacy, no one need be without use of his radio. Anyone in the system may, by lifting his microphone oft the hook, interrupt any conversation should an emergency make this necessary.