Self-contained Power Supply Research Articles

A Varidirectional Condenser Microphone

This condenser microphone has a self-contained power supply and uses hearing-aid type batteries. Cable connection is by means of a conventional 2-conductor shielded cable. The microphone, already somewhat more directional than a unidirectional microphone, can be made still more directional by applying an 18-in. long tubular attachment weighing only 5 oz. Total weight of unit, including mounting and windscreen, is 1 lb 12 oz. Open-circuit output voltage at 250-ohm tap is 1.6 mv/dyne.

A Mobile VideotapeRecording System

A system has been designed and constructional arrangements made for a special bus to contain a Videotape Recorder, two camera chains, signal generating equipment, director's console, monitoring facilities and self-contained power supply. System performance and accessory requirements are considered in detail. Various concepts in the use of the Videotape Cruiser are discussed, especially with regard to the advertising and motion-picture industries.

Telemetering System for the Measurement of Boundary Layer Noise

This paper describes a telemetering system for measuring boundary layer noise on a supersonic rocket sled. Conventional telemetering components were used for its construction. The acceleration present on a typical supersonic sled during a test period is 10g. The deceleration may reach 100g after the test period. The maximum sound pressure levels vary between 160 db to 170 db re 0.0002 microbar and the frequency range of interest is from 35 to 10 000 cps. The telemetering system is designed to operate from a self-contained power supply. The performance characteristics of the telemetering system are discussed with particular attention given to the selection and evaluation of a microphone for the measurement of boundary layer noise. [The work was sponsored by Air Force Contract No. 33(616)-3938.]

A Device for Direct Reproduction from Variable-Density Sound Negatives

The possibility of reproducing sound directly from the negative record offers an improvement in sound quality because it avoids the deterioration of definition, wave-shape, and volume range caused by the printing process. — In order to eliminate the distortion inherent in variable-density sound negatives, the playback amplifier must produce the same type of compensating distortion that occurs in good straight-line prints. The theoretical circuit requirements for an amplifier of this type are derived, and the RA-222 negative playback amplifier developed by the ERPI engineering department, in accordance with these requirements, is described. In addition to the basic distortion circuit, the RA-222 amplifier satisfies practical requirements, such as self-contained power supply and adjustments for negative gamma, amplitude, and frequency characteristic. — Experiences in various fields of use are reported, such as sensitometric measurements, print control, re-recording, and high-quality reproduction.