A Benthos Model 2214 bottom finding pinger provided sentinel altitude 

 information. It was thought that a continuously operating pinger might 

 interfere with interrogation of the acoustic releases so a modification was 

 made to the pinger to permit an adjustable on-off duty cycle. A circuit 

 was designed and installed in the pinger; an operating cycle of 19 seconds 

 on and 57 seconds off was selected. 



AMF/EG&G Model 322 acoustic releases were used for transponders. Eight 

 were selected for the operation, each with a different receiver channel. 

 Special attention was given to the two releases to be attached to the sweep- 

 line. The tilt function was disconnected in these two, and both were retuned 

 to receive a 9.0 kHz and transmit at 11.0 kHz. Also, the sensitivity was 

 increased to -92 dB/320 MV P/P (millivolts peak to peak) which later proved 

 to be a problem. The increase in sensitivity caused random pinging of the 

 transponders as they were being towed in the water. This was attributed to 

 flow generated noise. This problem was eliminated when the sensitivity of 

 the transponders was reduced to -88 dB/320 MV P/P. Command receiver channels 

 1 and 3 were chosen for the sweepline acoustic releases to minimize the 

 possibility of adjacent channel interface. 



The acoustic releases for the navigational markers were also retuned. 

 The reply frequency was set at 9.5 kHz for transponder "A" and 10.5 kHz for 

 transponder "B". Command receiver channels 7 and 5 were selected for trans- 

 ponders "A" and "B" respectively. A third marker, designated "C", was also 

 set up but never used. The remaining acoustic releases were prepared as 

 backups for the navigational markers and sweepline array transponders. 



The deck units used to receive each of the different transponder returns 

 were a AMF/EG&G 206A receiver and a AMF/EG&G 301 receiver. A AMF/EG&G Model 

 200 coder and amplifier connected to a AMF/EG&G 301 transducer were used to 

 interrogate the transponders. 



The 206A is a 4 channel receiver capable of simultaneous reception and 

 decoding of four discrete frequencies. The readout is in milliseconds. The 

 count is started when the interrogation pulse is sent out and each channel 

 stops when it receives a reply. The 206A was tuned to receive frequencies of 

 9.5 kHz, 10.0 kHz, 10.5 kHz and 11.0 kHz. 



The 301 receiver is a single channel receiver and displays bearing 

 and range in kiloyards. This receiver was modified so that the trigger pulse, 

 initiated by the 206A also reset the 301 receiver. The receive frequency for 

 the 301 was tuned to 10.0 kHz. The Model 301 transducer which was used is 

 permanently hull mounted on the USNS KANE. This arrangement of receiver 

 equipment was found to be workable. However, early on in the operation it was 

 discovered that interrogation range was very limited. Two miles from the 

 transponder net, the ship's engines had to be stopped and forv/ard motion had 

 to slow before return signals could be received from the transponders. 



Upon investigation, it was found that using the hull mounted 12 kHz 

 wide beam transducer and associated transceiver resultec much higher 

 signal to noise ratio. This eliminated the need to stop the ship's engines 

 in order to receive the transponder replies. The AMF/EG&G 206A receiver's 



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