[BC] FM History

[RichardBJohnson at comcast.net]

Edwin Armstrong invented a new method of encoding audio onto a transmission carrier. It had many advantages, amongst them being that the transmitter could operate in a high efficiency mode (class C) and the noise that often accompanied AM reception was practically non-existent when receiving a station.

Armstrong took his invention to a friend, David Sarnof, who was head of RCA and David promised he would help him develop it. RCA bought into the patents and helped Armstrong develop an experimental radio station.

However, it soon became evident that Sarnof and RCA were out to protect their existing AM radio empire and they did not want the competition from a new and much better form of radio. Years of costly legal battles ensued which RCA could afford and Armstrong could not. RCA closed down the station that they helped Armstrong build.

Because Armstrong greatly believed in his invention, he started to develop FM radio on his own. He sold rights to manufacture FM radios to several companies and Western Electric made his FM transmitters using their new "Frequency Watchman" techniques.

Before WWII, there were 50 FM stations on the air. Then the Japanese bombed Pearl Harbor. The ensuing war diverted resources and froze development.

After the war, David Sarnof and RCA, still out to hold control of their radio empire, pressured the FCC to change all of the FM radio frequencies from the 50 MHz band to 100 MHz a move they knew would instantly obsolete all of the exiting FM radios, and cause Armstrong to lose his personal investment in FM radio. Sarnoff claimed that he needed the existing FM frequencies for the new television. Even now, we do not have a TV channel 1 because it was unsuitable, requiring an unobtainable ten percent bandwidth for television. It later became the six-meter amateur radio band.

On January 31, 1954, Edwin Armstrong, gave up his long, taxing battle against Sarnof and RCA. He wrote a note to his wife apologizing for what he was about to do, removed the air conditioner from his 13th story New York apartment, and jumped to his death. A few weeks later RCA announced record profits.

Radio Corporation of America was still not through. Their development of television and the FM system for television audio showed their engineers the superior quality of FM radio transmission. The TV audio carrier was only 4.5 MHz away from the amplitude-modulated TV signal, which continually produced maximum power synchronizing pulses. Even a cheaper method of making TV sets, the "intercarrier" method, where the difference between the TV and audio carriers, i.e., 4.5 MHz was processed to recover audio, worked exceedingly well although RCA again pressured the FCC to revise the rules so that the TV carrier was never completely cut off by picture highlights which would cause an annoying buzz in their cheap receivers.

The success of inter-carrier sound prompted RCA to, again, get into the FM radio business. However, RCA had always tried to minimize the cost of radio and television sets. Until their demise, Analog TV transmitters needed receiver-correction filters to compensate for RCA's cheap IF amplifier characteristics as well as other rule-changes to make the transmission compatible with their cheap receivers. When RCA could save a few dollars in receiver manufacture, they would pressure the FCC to create new regulations to make radio and TV transmissions compatible with their cheap receivers.

RCA found that there was a very annoying hiss between stations when tuning the radio dial. They decided to tame it by putting a 0.005uF capacitor from their ratio-detector audio output to ground. This quieted some of the noise, but harmed the frequency response. Therefore, RCA petitioned (read pressured) the FCC to require pre-emphasis in all FM radio transmitters. It was experimentally determined that a 75 us pre-emphasis would compensate for the 0.005uF capacitor in their receiver circuits.

Many radio engineers were taught that FM required a pre-emphasis and de-emphasis to increase the S/N ratio. Nothing could be further from the truth. It was RCA FM receivers that needed to quiet the inter-station hiss. A simple squelch circuit as used by amateur radio operators worldwide would have done a better job. With pre-emphasis and de-emphasis, you decrease the dynamic range available during pre-emphasis. You never get it back.

Fortunately, RCA is no longer in business. Radio Corporation of America destroyed the lives of many famous engineers, including the inventors of modern-day television equipment, Vladimir Zworykin and Philo Farnsworth as well as Lee DeForest, the inventor of the modern radio receiver (he first put the grid into a vacuum tube). RCA used the power of the government, the courts, and its shareholders to do whatever it wanted. The NTSC color system was the last hurrah affecting the broadcast industry. It was designed to make cheap TV receivers. RCA RIP.

Cheers,
Richard B. Johnson
Book: http://www.AbominableFirebug.com/