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Abstracts of Technical Articles by Bell System Authors (01 January 1943)

01 January 1943

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Elec'l. Engg., Transactions Section, Proc. I. R. E., June 1942. September 1942. 136 ABSTRACTS OF TECHNICAL ARTICLES 137 obtained by use of a system having a volume range of 65 decibels and a frequency range from 60 to 8000 cycles per second. Substantially complete fidelity for the transmission of speech is obtained by a system having a frequency range from 100 to 7000 cycles per second and a volume range of 40 decibels. 

Preliminary experiments comparing a single-channel system and a twochannel stereophonic (auditory perspective) system showed that stereophonic transmission with an upper frequency limit of 5000 cycles per second was preferred to single-channel transmission with an upper limit of 15,000 cycles per second. A definite improvement was obtained in the stereophonic system by using three channels instead of two. A New Direct Crystal-Controlled Oscillator for Ultra-Short-Wave Frequencies.3 W. P. MASON and I. E. FAIR. An ultra-high-frequency crystal oscillator is described which utilizes a mechanical harmonic of an AT or BT crystal. 

With the oscillator frequencies as high as 197 megacycles, hormonics as high as the 23rd have been excited. Taking the second electrical harmonic of the oscillator, frequencies as high as 300 megacycles, or 1 meter have been obtained. Since a mechanical harmonic is used, the crystal can be of a practical size to handle and adjust. The harmonic vibration of the AT and BT crystals have as low a temperature coefficient as the fundamental mode, and temperature coefficients of less than two parts per million per degree centigrade are easily obtained.