MODEL QJB

The model QJB, shown in figure 1 below, is a searchlight type sonar equipment intended for installation in destroyers and destroyer escort vessels. This equipment is smaller than the QGB, and all its electronic units are housed in a single console. The QJB transmitter is much smaller than the QGB transmitter, because of the lower power requirements of the QJB. Although the transmitted power is less, the resultant echoes are equal to those of the QGB due to the higher sensitivity of the crystal transducer of the QJB. The transmitter is mounted in the lower right section of the console. The other units in this console are the receiver, keying unit, bearing deviation indicator, indicating range recorder, remote training control, and power supplies.

The receiver is of the sum and difference type and has both time-varied-gain (TVG) and reverberation-controlled-gain (RCG) features.

The QJB utilizes the unicontrol-oscillator system for tuning the receiver and transmitter. The operating frequency need not be tuned carefully to the frequency of the crystal transducer because the transducer has a rather flat resonance curve-about 6 Kc wide.

The chief difference in the appearance of the QJB console as compared with the QGB is the manner in which the BDI cathode-ray tube is mounted. The QJB mounting is shown in figure 2. The tube is located in the center of the bearing circle so that the operator does not have to shift his eyes away from the bezel indicating the transducer bearing when he wishes to see the BDI indications. To mount the BDI cathode-ray tube in the center of the bearing indicator-which consists of a true-bearing circle and a bezel ring that indicates the transducer bearing-a complicated mechanical system is required.