AM RADIO COMES OF AGE

by Dick Reiman, Historian

Following the success of the KDKA and RCA early broadcasts, there was a rash of requests for station licenses. The Department of Commerce recognized broadcasting stations as a distinct class and began to license them on a single frequency, 833 kHz. By 1921, twenty-eight stations had been granted licenses. Stations were started in New York, Chicago, Boston, Pittsburg, Detroit, Los Angeles and San Francisco. Interference was so severe that a new approach utilizing more frequencies and regulating power levels was begun. In 1922, an additional channel, 750kHz, was added and 1000 watts was the maximum power level. By 1924, the entire band from 550kHz to 1500

kHz was allocated and three levels of power, 5000, 500 and 100 watts were established.These became the designations of "clear", "regional" and "local". Finally, the Radio Act of 1927 gave the FRC necessary power to regulate the technical operations of stations.

How was the broadcasting business to be financed? Was the government to own and operate the stations with tax money, would advertising pay for the private ownership, would universities operate the stations as part of the education budget, or would the radio receiver manufacturers operate them as an incentive to sell the sets? In Europe, public ownership won out with such government organizations as the BBC. Broadcasts using advertisement was first thought to be "unseemly" by Commerce Secretary Herbert Hoover, and "unthinkable" by David Sarnoff. But advertising became the principle economic basis of radio broadcasting, with some additional regulation compared to other media such as newspapers and magazines.

Early radio broadcasting technology was primitive but gradually improved with radio's commercial success. The power transmitters used the low-level grid modulation method developed by AT&T for radiotelephony. Most of the power appeared as heat on the anode of the final amplifier tube, and had to be dissipated by a watercooled jacket, with the water being distilled so as to be nonconducting with meticulously cleaned ceramic plumbing also neccessary. Transmitting antennas were first just simple tower structures with long wires strung on poles.Later, importance of good grounding was employed to improve transmission efficiency. Multitower directional antennas also came later. Radio receiver design started with the "Cat's Whisker" crystal detector with no electron tube amplification. Earphones were used in place of loudspeakers and the energy to operate them came from the audio wave. A strong signal was required and only nearby stations could be received. A cylindrical oatmeal box became the form for the tuning coil. Armstrong's regenerative detector was used by some but was limited due to its tendency to "howl" when improperly adjusted. With a tuned radio frequency receiver, each stage of amplification had to be tuned, then retuned to the desired station. Telephone earpieces mounted on the throat of a horn were replaced by moving coil speakers. Finally, Armstrong's superhetrodyne circuit and 120 Volt AC Power Supplies revolutionized receiver radio

design.