During these years Sarnoff was also locked in a struggle with one of the geniuses of radio technology, Edwin Howard Armstrong, the man who wrested revolutionary powers from De Forest's vacuum tube. Armstrong had never stopped inventing. In 1918 he devised a method for amplifying extremely weak, high-frequency signals—the superheterodyne circuit. Then in the early 1930s he figured out how to eliminate the lightning-caused static that often plagued radio reception. His solution was a new way of imposing a signal on radio waves. Instead of changing the strength of waves transmitted at a particular frequency (amplitude modulation, or AM), he developed circuitry to keep the amplitude constant and change only the frequency (FM). The result was sound of stunning, static-free clarity.
Once again Sarnoff tried to buy the rights, and once again he failed to reach an agreement. His response this time was to wage a long campaign of corporate and governmental maneuvering that delayed the industry's investment in FM and relegated the technology to low powered stations and suboptimal frequencies. FM's advantages eventually won it major media roles nonetheless—not only in radio but also as the sound channel for television.
The engineering of radio and television was far from over. The arrival of the transistor in the mid-1950s led to dramatic reductions in the size and cost of circuitry. Videocassette recorders for delayed viewing of TV shows appeared in 1956. Screens grew bigger and more vivid, and some dispensed with cathode-ray technology in favor of new display methods that allowed them to be flat enough to hang on a wall. Cable television—the delivery of signals by coaxial cable rather than through the air—was born in 1949 and gained enormous popularity for its good reception and additional programming. The first commercial telecommunications satellite began service in 1965 and was followed by whole fleets of orbiting transmitters. Satellite television is able to provide far more channels than a conventional TV transmitter because each satellite is allocated a big slice of the electromagnetic spectrum at very high frequencies. With all new wireless technologies, finding room on the radio spectrum—a realm that ranges from waves many miles long to just a millimeter in length—is always a key issue, with conservation growing ever more important.
By century's end the move was toward a future known as high-definition television, or HDTV. The U.S. version, to be phased in over many years, will bring television sets whose digital signals can be electronically processed for superior performance and whose images are formed of more than a thousand scanned lines, yielding much higher resolution than the current 525-line standard. Meanwhile, TV's reach has extended far beyond our world. Television pictures, digitally encoded in radio waves, are streaming to Earth from space probes exploring planets and moons in the far precincts of the solar system. For this most distance dissolving of technologies, no limits are yet in sight.