. Basic methods for the calibration of sonar equipment. LQUII'MENT AT MOUNTAIN LAKES 83 ,ZERO SIGNAL / CONDITION MREP! PERI I I ^ZERO VOLTAGE. FiGURK 18. CilTUil SlIU'llKIlK III llu' |)UlsC TCHiliCl. I 111' voltage wave loim ol llic pulse is iiulicileil .\t \arioiis points in the circuit. become almost wholly discharged between pulses. Hence, the grid signal is a saw-tooth wave, the am- plitude of which can change rapidly with change in the incoming pulse. l^he first section of the acts as an impedance changer and phase in\erter, the voltage at pt)int c still containing the d-c and a-c c
. Basic methods for the calibration of sonar equipment. LQUII'MENT AT MOUNTAIN LAKES 83 ,ZERO SIGNAL / CONDITION MREP! PERI I I ^ZERO VOLTAGE. FiGURK 18. CilTUil SlIU'llKIlK III llu' |)UlsC TCHiliCl. I 111' voltage wave loim ol llic pulse is iiulicileil .\t \arioiis points in the circuit. become almost wholly discharged between pulses. Hence, the grid signal is a saw-tooth wave, the am- plitude of which can change rapidly with change in the incoming pulse. l^he first section of the acts as an impedance changer and phase in\erter, the voltage at pt)int c still containing the d-c and a-c components of the rectified signal at b. The a-c component of this volt- age is applied to the grid of the second section of the 6SN7 through the RC netwoi k. I'he time constant of this RC coiiibiiKition should l)e approximateh e(|ual to that of the filter section. B\ ])i()|)er adjiistinent, the signal at d can be made e(|ii:il lo the a-c compon- ent of the signal at roximateh equal to one-half the d-c component of the voltage at c with the a-c componeiils balanced out. To facilitate this adjustment, a terminal is su]jplied for observa- tion with a cathode-ray oscilloscope. An increase in the intensity of the receiv ed acoustic signal causes the d-c voltage at e to rise. The thyra- tron control ciicuit used with the pulse system re- quires, however, a decrease in the d-c voltage with in- crease in signal intensity and. for this reason, the final tube shown is used. In order to be used with the pulse system, one of the thvratron control circuits is modified and a single coaxial jack installed to take the d-c output of the pulse rectifier. A switch on the front of the |>anel allows the operator to choose the output of either the recorder circuit or the ]ndse rectifier, ^\'hcn the latter is chosen, 50-ohm resistors are automatically inserted to slow the pen-drive so that the recorder will not hunt. Ihis reduces the speed of the lecorder from 100 to some 30 dl) per second. .\ gai
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