| 摘要 |
A signal monitoring instrument (10) includes two input terminals (38) and (40) for receiving two external signals and includes an oscillator output terminal (42). When the instrument is placed in the level mode of operation by depressing a level push button (18) the instrument (10) produces an audible sound having two tones to indicate that a first external signal applied to terminal (38) is not at a desired voltage level. If the frequency difference between the tones is less than a predetermined amount, a beat sound is produced. The absence of two tones and the absence of a beat in the audible sound indicates that the external signal applied to the terminal (38) is at the desired voltage level. When placed in the azimuth mode by depressing the azimuth push button (20), the instrument (10) will produce an audible sound having a frequency inversely proportional to the phase difference between two external signals applied to the two terminals (38) and (40).
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