M. J. Tucker and A. R. Stubbs 317 
improves the signal-to-noise ratio. The electrical input to the transmitting 
transducer is between 1 and 2 w, the frequency deviation is 21 to 36 kcps, and 
the audio-frequency temperature signal varies between 200 and 800 cps. 
The receiving transducer is slipped down the towing warp after this has been 
fully let out, and thus needs no extra men for its operation. After preamplifi- 
cation, the received signal is fed to a low frequency radio receiver whose dial 
reading is a measure of the depth. The output of the radio receiver is the audio- 
frequency temperature signal. A depth accuracy of 1% and a range of one mile 
is claimed for the instrument. 
For some purposes, suchas the seismic refraction shooting method described 
in Section 16.2.4 for examining sub-bottom geology, there are advantages in 
placing a hydrophone on the sea bed. Dow [19] has also designed an acoustic 
telemetering hydrophone for this application. It will receive sounds in the range 
50 cps to 5 kecps and transmit these onanacoustic carrier of 21 kcps. It is capa- 
ble of working at depths of up to 3000 fathoms, and uses a power input to the 
transducer of about 30 w. 
16.5. MISCELLANEOUS APPLICATIONS 
16.5.1. Wave Recording 
An inverted echo-sounder placed on the sea bed and pointing upward at the 
surface may be used to record wave height. The height recorded is the distance 
= = — ee 
ft 
en 
fraction by internal waves. 
