No Interference

Edwin Howard Armstrong, bald, blue-eyed, well-heeled professor of electrical engineering at Columbia University, has made a tidy fortune for himself by inventing the super-regenerative and superheterodyne radio circuits. For the last 25 years he has been working on the problems of static, interference, tube noises and fading. Some time ago, in an effort to get perfectly clear reception, he devised a system of frequency modulation in the transmitter. According to standard broadcasting technique, which relies on amplitude modulation, this was heresy.

Frequency modulation can be described as changing the length of the radio wave. Amplitude modulation changes the wave's strength. Interference noises can simulate amplitude modulation and therefore disturb signals broadcast by this system, but they do not simulate frequency modulation. Thus frequency-modulated signals skip neatly past the interference, whether lightning bolt or icebox motor. One catch is that ultrashort wave length of limited range must be used.

Last year Professor Armstrong built himself a 400-ft. tower on the Hudson River Palisades at Alpine, N. J.. began sending out experimental frequency-modulated programs. In a few experimental receivers they came in crystal clear, in every kind of weather. From the tower at Alpine the reception range is about 100 miles.

Commercial broadcasters, who use only amplitude-modulating transmitters, have so far only nibbled at the Armstrong system. But the high-fidelity, interference-free programs from Alpine have created such a stir that General Electric Co. (licensed by Armstrong) started to make receiving sets which could be switched from commercial reception to frequency modulation. Last week these were put on sale in Newark, and this week they will be launched in New York. Price: $75 to $225. Stromberg-Carlson is also preparing to put sets on sale. Besides Alpine, two other frequency-modulating broadcasting stations (at Paxton, Mass, and Hartford, Conn.) are underway and others (Buffalo, Syracuse, Albany, Washington, Milwaukee) are scheduled to get going soon. And some admirers of the Armstrong system predict that by next Christmas most radio purchasers within the 100-mile range of a station will insist on double-duty sets (both ordinary and Armstrong receptions).

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