The Beginnings of FM Radio Broadcasting
owl writes:
http://www.theradiohistorian.org/fm/fm.html
Before FM, There was APEX
In the early and mid-1930s, radio communication was confined to the Low [or Long] Waves (100-500 kHz), Medium Waves (500-1500 kHz), and the Short Waves (1,500 to 30,000 kHz). The frequencies above that, referred to as the "ultra-high frequencies", were truly the "Wild West" of radio. It was a place for experimentation and a possible home to future radio services. Commercial broadcasting to the public took place entirely on the standard broadcast band (540-1600 kHz), but it was affected by a number of defects that annoyed the public - natural and man-made static, local and skip interference, atmospheric fading, and limited fidelity. Starting about 1932, a number of brave and daring broadcasters sought permission from the FCC to conduct experiments in the Ultra-Short Waves in an attempt to find solutions to these problems. In particular, these experimental stations wanted to transmit wideband, high fidelity audio. Amplitude modulation, the only known method of transmitting audio at the time, was the method utilized on these so-called "Apex" stations. Experimental licenses were being issued for up to 1,000 watts on frequencies at 25-26 MHz and 42 MHz. By 1939, these Apex stations were operating in 34 U.S. cities in 22 states They suffered less skip interference than standard AM stations, but static was still a problem.
At the same time that these Apex broadcasters were gaining a foothold in the upper frontiers of the radio spectrum, an entirely new type of radio service was also being demonstrated - one that was destined to cause Apex AM to become obsolete. That service was called Frequency Modulation, or FM.
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