Wavelengths of American Stations Change

Radio Record, Volume II, Issue 21, 7 December 1928, Page 31

Wavelengths of American Stations Change

JN order to meet. the intense congestidn in the United States, it was planned to change the wavelengths of nine-tenthy of the broadedsting stations: from Armistice Day, It. was claimed that the temporary inconvenience caused would bé more than recompensed by the clearét réception. To understand the plan upon which the new allocations are based, it is necessary to know that thete ate ninety-six, channels or highways in the broadeast spectruni between. 550 and 1500 kilocycles, that is, between the wavelenzths .of 545 metres and 200 metres. Hach of these channéls is 10 kilocycles wide, the modulating or sound frequency extending for five kilocycles on either side-on the carrier’ wave.

When two stations are radiating energy on the same channel, or on ap+ proximately the same wavelength. a collision occurs, and a high pitched squeal results. Listeners will rémember such an occurrence in New. Zealand when 3YA was being heterodyned by a Sydney variation. Of the ‘ninety-six channels, six are assigned exclusively to. Canada, leaving 90 to the use of the six hundred and twénty-four stations in the United States and Alaska, an average of nearly seven stations pér channel, The inevitable result was that there was hardly an American station that could be heard without a- heterodyning whistle. Here was the problem which faced the Commission which has just completed its investigations. There were two solutions to the problem. One.was to reduce the time that somé of the stations were to operate, and the other was to reduce thé number of stations on the air. The

Radio Commission chose the: former plan. Forty channels were cleared, eight in each zone, or section of the country. One-fourth of these were assigned exclusively to the use of single stations. Of the other thrée-fourths, two or more stations are limited in time -so

that they: do not ‘operate: simultaneously. Most of them are highpowered stations. Consequently, during the night hours, there shoul. ‘be little or no interference on néarly half the dial. The remaining channels are allocated so as to provide for a _minimum of interference.