Crystal-controlled pump signal source for an experimental parametric acoustic receiving array

Abstract

In the Parametric Acoustic Receiving Array (PARRAY), a locally generated, high-frequency carrier (or pump) wave is modulated in the water by a low-frequency acoustic wave. The information in the low-frequency signal appears as low-level modulation side bands of the pump wave; therefore, the side-band noise of the pump-signal source is an important PARRAY system parameter. Since commercial oscillators with adequate spectral purity were not available, a program was initiated to develop a 65-kHz crystal-controlled oscillator with sufficient spectral purity for use as the pump-signal source in an experimental PARRAY. Application of state-of-the-art techniques and components has enabled the design and construction of a crystal-controlled oscillator with spectral purity previously unattainable in this frequency region. Spectral purity of this oscillator is approximately four orders of magnitude better than commercially available oscillators in the 65-kHz frequency region. Measurements performed on the oscillator show that the spectrum level side-band noise referenced to the carrier level is better than −170 dB for frequencies greater than 100 Hz away from the carrier. The oscillator design is described in detail and side-band noise test data are presented and discussed. [This research was supported by the Advanced Research Projects Agency of the Department of Defense and was monitored by the Naval Electronics Systems Command under Contract NO0039-76-C-0231.]