GB1205569A - Improvements in or relating to stethoscopes - Google Patents

Abstract

1,205,569. Stethoscopic amplifier. E.M.I. ELECTRONICS (CANADA) Ltd. 12 Oct., 1967 [10 Nov., 1966], No. 50427/66. Headings H4J and H4R. In a stethoscope having an input transducer 1 (Fig. 1), an output transducer 8<SP>1</SP> and two oscillators 3, 4, the oscillations generated by the first oscillator 3 are frequency modulated by the electrical signals from the input transducer 1. The second oscillator 4 generates oscillations at the (unmodulated) frequency of the first oscillator 3. The outputs from both oscillators are passed through a mixer 5 and a filter 6 which selects signals at the difference frequency. Such difference frequency signals are applied to an output transducer 6 to provide an output acoustic wave pattern related to the input acoustic wave pattern but translated in frequency thereto so as to lie in a more easily audible frequency region. In operation and in the absence of an incident wave pattern, there is substantially no audible acoustic output wave pattern. Alternatively, a suppressed carrier amplitude modulator 10 (Fig. 3) modulates the amplitude of the oscillations generated by a first oscillator 9. A mixer 5 mixes the outputs from the modulator 10 and from a second oscillator 4 which generates oscillations at a reference frequency. The difference frequency is selected by a filter 6. The output transducer 8<SP>1</SP> provides an output pattern related to the input pattern but translated in frequency so as to lie in a more easily audible frequency region. In operation and in the absence of an incident wave there is substantially no audible acoustic wave pattern. The input transducer may be of ceramic type. An output point 7 permits direct monitoring of the input signal. A transistorized circuit of the stethoscope of Fig. 1 is given in which the oscillators 3, 4 comprise astable multivibrators (Fig. 2, not shown). There may be selective input and/or output filtering to discriminate different types of signal, amplitude compression to emphasize low level signals, and automatic gain control to compensate for signal variation from one patient to another. The output signal may be recorded on disc or magnetic tape for reference.