Radio Receiver

Frequency modulation, which is the most popular form of mass radio communications now in use, actually was developed and demonstrated in 1933 by Edwin H. Armstrong.
Within a decade, there was an impressive increase in its use. By the summerof 1940, there were roughly 50 FM stations on the air, all operating with limited hours, and on an experimental basis. FM became widely recognized as a static and noise-free communications medium, although both the transmitting and receiving equipment in use at that time was primitive by todays standards.
In 1941, the Federal Communications Commission authorized the first regular or non-experimental stations, and by 1945, most FM stations held regularl icenses. Because of the war, there was very little FM development until about five years later. Immediately following the war, there was a rush for construction of new FM stations, probably because of the encouragement and support given the medium by the FCC. There was also fear among some broadcasters that the FCC might replace the AM service with all FM outlets.
Almost all of the FM stations in existence at the time were co-owned by AM operators, and simulcasted the AM programming.When the FM's brought no additional revenue to their owners, the number of FM stations after 1950 took a downturn that lasted several years. Radio station revenues increased after the war, but the number of stations on the air increased much faster. This resulted in a marked decline in the average income per station. In the decade between 1950 and 1960, FM's situation remained about constant. People who listened to FM did so mainly because there were very few commercials, and it was largely recognized as a distributor of educational, classical or better music programming.
On June 1, 1961, the FCC authorized FM broadcasters to begin stereo broadcasting. In anticipation of the event, when the authorization was granted, three stations commenced stereo broadcasting at midnight local time. SCA (sub-carrier authorization) was widely used, because it afforded the FM broadcaster the opportunity to supplement his income by offering services on his subcarrier that could not be heard without the use of special receivers. Subscribers to this service paid a leasing fee, and were provided commercial-free background music for their businesses. SCA is still an option open to FM broadcasters. In larger areas, many FM operations use a subcarrier for distribution of readings for the blind, and the receivers for this are federally-funded.SCA's are in popular use today for telemetry/data. Stations whose transmitters are away from the studio site can use telemetry transmitters to send back metering data so the operating parameters can be monitored.
In stations with SCA's, the main-to-subchannel crosstalk, or the other way around, was an issue that had to be addressed, and problems here really showed up. Keeping the old stereo generators aligned was a constant headache. Very little stereophonic programming material was available at this time, and stereo consoles and processing gear was in short supply. Many engineers of the old school cursed stereo because any defects in the stereo phasing stuck out like a sore thumb on FM monaural receivers. I once heard a 30 second period of silence on an FM station. Thinking they had gone off the air, I called the station, and they said no such event had occured. It then came to me that I was listening on an FM portable monaural receiver, and during that time, a spot was on the air that was 180 degrees out of phase! This is why it is imperative that phase relationships be dealtwith carefully.
The authorization of FM stereo did not work overnight magic to a medium that was suffering, but it had a far more profound effect than the advent of AM stereo. So much so that by the mid 1970's, FM had surpassed AM in terms of listenership. As FM equipment became more refined, it became even more popular as an entertainment medium. This period saw soaring sales of stereo radio receivers, as well as the popular personal portable stereos. It is not uncommon today to see a station that sold for $40,000 in the mid 1960's to be worth well over $1 million today.

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