The hydrophone is an omnidirectional barium- 
titanate unit with a sensitivity of -85 db 
reference to one volt per microbar. When ter- 
minated in a 20-megohm load, the response is 
essentially flat between 10 cps and 2 kc. 
The hydrophone signal is amplified in a 
hybrid preamplifier stage which provides a 
voltage gain of 280. A vacuum tube is employed 
in the input stage in order to achieve the 
necessary high input impedance and low equiva- 
lent noise input. A Sylvania 5904 subminiature 
triode with a 24-volt filament and plate supply 
eliminates the need for a special vacuum tube 
plate supply. This tube is powered directly 
from the transistor amplifier supply. The 
equivalent noise input of the preamplifier re- 
ferred to the input grid over a 600-cycle 
bandpass is less than one-half microvolt. 
The voltage gain from the hydrophone pre- 
amplifier input to the rectifier/integrator 
circuit is approximately 100,000, and the dy- 
namic range of the voltage amplifier and filter 
channels up to the rectifier/integrator input 
is 95 db. The rectifier/integrator circuit has 
a useable dynamic range of 40 db with correc- 
tions for nonlinear operation and is linear 
over a 30-db range. 
WAVE- HEIGHT MEASUREMENT 
A qualitative measurement of wave height 
is accomplished by means of a small transis- 
torized depth sounder operating at 198 kc. 
The transducer is mounted in a small buoy which 
can be either fastened directly to or floated 
upward above the main buoy hull. The trans- 
ducer beam is directed upward and uses the 
underside of the air-water interface as the 
reflecting surface. The rotating neon lamp 
wave-height indication is converted to a linear 
display providing a measurement of the wave- 
height in one-foot increments. The wave-height 
data is displayed in the data photo matrix 
along with the acoustic digital display and 
main counter reading. The wave-height recording 
extends for a period of 15 seconds during each 
measurement cycle. 
DATA CONVERSION AND PHOTO- RECORDING SYSTEM 
The analog-to-digital conversion of the 
acoustic level measurements is recorded on 
35-mm film in digital form. The digital en- 
coding is accomplished by a l2-bank, 52-point 
stepping switch and a matrix of neon lamps. 
The lamp matrix consists of four rows of eight 
lamps. Six lamps in each row are used in a 
six-bit gray code. The seventh lamp is used 
to provide a parity check, and the eighth 
lamp provides for channel identification. 
23 
Seven banks on the stepping switch are used 
to provide the grounding pattern for the binary 
code on the lamp matrix corresponding to the 
switch wiper arm position as it steps through 
the 52 levels. One bank contains a precision 
resistor divider network providing one db step 
changes in the voltage level picked off by the 
wiper. Therefore, the voltage picked off the 
divider network at any switch level is repre- 
sented simultaneously by the binary digital 
code established in the neon lamp matrix through 
the grounding pattern. 
The voltage picked off the precision resistor 
divider network in the stepping switch is com- 
pared to the voltage stored in the integrator 
capacitor. As the stepping switch operates, 
the divider voltage eventually equals or slightly 
exceeds the capacitor voltage at some particular 
switch level. At the balance or crossover point, 
the voltage comparator circuit discharges a 
capacitor through the neon lamp matrix. The 
binary code corresponding to the integrator 
capacitor voltage is exposed on the film by the 
flash of the appropriate lamps. 
The programmer selects and applies each 
integrator output sequentially to the voltage 
comparator and the corresponding row in the 
digital matrix. Each film frame, therefore, 
contains the digitized spectrum level from each 
of the four bandpass filters. 
RECOVERY SYSTEM 
Buoy recovery will be effected in three 
phases. Assuming the general situation in 
which the buoy is moored in the open ocean, the 
first phase in recovery is essentially a navi- 
gation problem in which the recovery ship must 
return to the general area where the buoy is 
moored. The first stage is accomplished by use 
of ordinary navigational methods (LORAN, DF 
bearings, celestial navigation, radar fix, 
soundings, etc.), employing whichever methods 
are best suited to the particular conditions at 
hand. The second phase in recovery results in 
release of the buoy and its return to the sur- 
face in a free-floating condition accomplished 
by an acoustic interrogation from the recovery 
ship. The third recovery phase required 
localization of the buoy on the surface and sub- 
sequent retrieval by the ship. 
Each phase in the recovery procedure requires 
the solution of particular interrelated pro- 
blems in order to achieve reliable operation. 
The navigational accuracy requirements are 
determined primarily by the acoustic interroga- 
tion ranges which can be achieved and secon- 
darily by the localization and visual sighting 
aids employed when the buoy is on the surface. 
