This action causes the counting register to count from zero, one count for each yard of travel 

 of the acoustic pulse coming from the submarine. Ten msec after the acoustic pulse is re- 

 ceived by the ranging receiver, a pulse is sent to the range counter, triggering Q-3 to the zero 

 state and causing a transfer of the number in the counting register into the storage register. 

 This number is decoded and displayed visually. 



RANGING RECEIVER 



This receiver is used to distinguish the ranging signal pulse from the accompanying 

 background noise, a noise which may include transients similar to the signal. 



This function is difficult to perform because of the complex nature of the signal-to- 

 noise (S/N) ratio. One source of noise is sea ambient and its characteristics may vary with 

 time; other noise is generated by the submarine and is a function of range and other factors. 



Since both signal and noise vary by many decibels, a large amount of automatic gain 

 control (AGC) is incorporated into the ranging receiver to enhance detection of the ranging 

 pulse. Because this AGC action is slow, the gain is not reduced upon receiving a transient 

 such as the signal pulse. 



The signal flow is illustrated by Figure 8, which first shows a shielded preamp. This 

 preamp is tuned to both 10.6 kc and 50 kc, and it may be manually varied in gain to compen- 

 sate for various ambient conditions. 



A stepped AGC amplifier, which consists of four cascaded gated amplifier (GA) stages, 

 follows. Each stage has the capability to be switched electronically from 15-db gain to 0-db 

 gain. As the input level rises or falls, a series of level amplifiers and detectors (LAD) sense 

 the change and automatically switch the gain of the gated amplifiers accordingly. The 

 stepped AGC amplifier maintains its output level between -23 dbv and -3 dbv for an input 

 level variation of up to 75 db. 



Following the stepped AGC is a tuned, continuously variable AGC which controls its 

 output level within 3 db for a 30-db variation at the input. This AGC, as well as the stepped 

 AGC, passes any short transient without attenuation. 



The resulting transients, including the signal pulse, are measured for minimufn level 

 and minimum pulse length by an integrating energy level detector. Any pulse surviving these 

 two cnecks is considered to be a signal pulse, and a data transfer signal is sent to the range 

 counter. 



CURRENT AND FUTURE DEVELOPMENT 



As space is always a problem on board ship, plans are being formulated so that a sub- 

 stantial savings in space can be obtained for both portions of the system. Studies are being 

 made of miniaturization techniques to determine which is best suited in terms of size and 

 weight savings versus reliability and cost. 



10 



