. Basic methods for the calibration of sonar equipment. EQUIPMENT AT MOUNTAIN LAKES 77 COAXIAL JACKS. Figure 12. Ciicuit sdieniatic of coupling amplifier. This anijjlilier provides exUemely high in|)ut iiiipctlances lor operation in balaiiLCil or uiibalanceil circuits. Design considerations in the construction of tliese required the selection of a mid-frequency of 97 kc. The detector tuning oscillator of the signal generator of system 2, therefore, supplies a frequency of 747 kc. A rotary switch permits the rapid selection of any of the three band-pass filters, which have widths of 10, 300, an
. Basic methods for the calibration of sonar equipment. EQUIPMENT AT MOUNTAIN LAKES 77 COAXIAL JACKS. Figure 12. Ciicuit sdieniatic of coupling amplifier. This anijjlilier provides exUemely high in|)ut iiiipctlances lor operation in balaiiLCil or uiibalanceil circuits. Design considerations in the construction of tliese required the selection of a mid-frequency of 97 kc. The detector tuning oscillator of the signal generator of system 2, therefore, supplies a frequency of 747 kc. A rotary switch permits the rapid selection of any of the three band-pass filters, which have widths of 10, 300, and 6,000 c, centered at 97 kc. Following the filter circuits are three stages of amplification termi- nating in a 135-ohm output circuit. Monitor Converter System 2 is provided with a converter circuit com- prising a modulator and a local oscillator which may be varied continuously from 94 to 100 kc. The prim- ary function of this circuit is to permit aural monitor- ing of supersonic frequencies by converting the normal 97-kc signal output of the detector circuit, to an audio frequency range of 0 to 3,000 c. Indicator The use of narrow-band crystal filters in the de- tector circuit makes it necessary to center the output of the second modulator precisely on the mid-fre- quency. The adjustment of the detector-tuning oscil- lator to accomplish this is referred to as "tuning the detector" and it is correct when maximum detector output is obtained. It has been found expedient to provide for a continuous visual indication of this adjustment. This indication is produced by taking a portion of the detector output signal from a constant voltage source in the recorder circuit and modulating it with a signal from a crystal-controlled oscillator tuned to the mid-frequency of the crystal filter in the detector circuit. The resultant difference signal is rectified and impressed on an electron-rax tube. The shadow angle of this tube ojjens and closes at the difference fre- quency. T
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