THE DESIGN AND INSTALLATION OF THE FIXED ACOUSTIC BUOY 
by RICHARD P. OBERLIN 
Project Engineer, Fixed Acoustic Buoy 
The Martin Company, Baltimore, Maryland 
ABSTRACT 
The Fixed Acoustic Buoy is a deep sea instru- 
mentation device which measures acoustic data 
at a depth of 14,000 feet. It is controlled and 
powered from shore via a cable and has numer- 
ous modes of operation. Signal processing is 
accomplished in the deep sea unit to allow use of 
a single coaxial cable. The paper describes the 
electronic system design and the techniques used 
to protect the components from the high ambient 
pressure while still allowing electrical intercon- 
nections. The installation technique and prob- 
lems encountered are also discussed. 
INTRODUCTION 
System design of deep ocean acoustic equip- 
ment is impaired by lack of data at the desired 
depths. The Fixed Acoustic Buoy (FAB) is a 
system which was designed for the Navy to obtain 
some of this missing data. The data itself and 
the types of tests involved are classified and will 
therefore not be discussed in this paper. 
The great significance of FAB, as far as 
oceanographic instrumentation is concerned, is 
that it is a radical design departure from normal 
practice. In FAB almost all of the signal proc- 
essing is accomplished electronically in the deep 
sea portion. This results in a considerable cost 
saving because it allows use of a single coaxial 
cable with medium bandwidth requirements 
instead of 21 pair medium bandwidth cable or 
one high bandwidth coaxial cable with 21 channel 
multiplexing. The suitability of this approach 
has been considerably strengthened with the 
successful implantment of the system during 
December 1960 in 14,000 feet of water south of 
Bermuda. System operation and data collection 
has continued since that time ina satisfactory 
manner. 
SYSTEM DESCRIPTION 
The system consists of a bottom unit, a co- 
axial cable and shore equipment. The bottom 
unit is shown in Figure 1. It consists ofa 21 
element vertically steerable acoustic array, a 
buoyancy tank to hold the array vertical, a pres- 
sure tight sphere housing the electronics and 
beamforming networks, a battery, a tilt indicator 
and an anchor. 
The cable consists of about 27 miles of coaxial 
cable which is similar in construction and char- 
acteristics to the A.T. & T. Trans-Atlantic tele- 
phone cable linking the United States and Europe. 
Slightly over one mile of this cable is double 
armored and magnetically shielded. The remain- 
der is single armored with no magnetic shielding. 
The shore equipment consists of the control 
circuitry, data recording equipment and power 
supplies required to manually operate the system. 
The shore equipment is located on a Texas Tower 
type structure called "Argus Island". 
Five normal control functions are available to 
the shore operator, as Shown in Figure 1. These 
are steer forward (a command for the deep unit 
to acoustically look at the next higher angle), re- 
set (a command to return to the lowest angle), 
steer feedback instrumentation on and off, tilt- 
pitch instrumentation on and off, and tilt-roll 
instrumentation on and off. The commands are 
initiated by sending the appropriate frequency (in 
the range of 10 to 12 KC) down the cable to the 
sea unit. An additional function ("fail safe") is 
commanded by a reversal of the power supply 
voltage to the deep unit. This causes a large 
portion of the circuitry to be bypassed in case of 
a failure. 
Fifteen different modes of acoustic data col- 
lection can be commanded via the steer channel. 
Thirteen of these are narrow listening beams at 
various vertical angles from 0° to 90°. The last 
two are omnidirectional listening modes. In 
"fail safe" operation, only the 0° beam is avail- 
able. The acoustic data is acquired in the range 
of 400 cps to 5 KC. 
The instrumentation functions answer back 
with FM signals in the range of 6 to 8 KC. Steer 
feedback tells which particular step the beam is 
on and the tilt channels give the tilt of the array 
from vertical in.two mutually perpendicular axes. 
The block diagram of the system is shown in 
Figure 2. As can be seen, the DC power and 
