cord the audio information from one of the hull- 
mounted hydrophones. The second hydrophone, 
mounted diametrically opposite the first on the 
eylindrical midsection, was connected to the in- 
put of channel 2 on the tape recorder, A fre- 
quency-modulated signal containing depth informa- 
tion and operating with a carrier frequency of 
13.5 ke was also recorded on channel 2. This 
depth information originated in a pressure trans- 
ducer and associated circuitry. 
Depth Measurement Circuitry 
Channel 2 was specially adapted by appro- 
priate filtering to record flow-noise data in 
the region below 6 ke and to record depth and 
time information in the region above 10 kc, using 
a frequency-modulated 13.5-ke carrier. A func- 
tional diagram of the depth-measurement circuit 
is shown in Fig. 6. 
From the recorded pressure and time informa- 
tion the depth and velocity of the missile was 
determined for any time during the missile's fall. 
The carrier frequency of 13.5 ke was modulated by 
a 200-cps voltage the amplitude of which was de- 
creased linearly with water pressure by means of 
the pressure potentiometer (Fig. 6). The 200-cps 
frequency which modulated the 13.5-ke carrier 
was used as a time reference by demodulating the 
tape information and counting the number of cy- 
cles during any desired data period. The ampli- 
tude of the 200-cps voltage from the pressure 
potentiometer determined the frequency deviation 
of the FM carrier. Upon demodulation, the 200- 
eps amplitude was proportional to pressure and 
therefore to depth. Velocity and acceleration 
were calculated from depth and time data. 
The 200-cps oscillator, the 20-db amplifier, 
the 14-db amplifier, and the varicap modulator 
were designed and built by this laboratory. De- 
tailed schematics of each of these units are 
shown in Figs. 7-10, 
The most critical unit in the depth-informa- 
tion system was the 200-cps oscillator. The 
frequency of this oscillator had to be an ac- 
curate 200-cps. The final design showed an ac- 
curacy of 1% in laboratory tests. For accurate 
depth information it was necessary that the 
amplitude of the oscillator remain stable from 
the time of the field calibration (described 
later in this section) to the end of the drop. 
Small changes in oscillator amplitude from day 
to day were of no concern. 
The pressure potentiometer was a commercial 
12 
transducer, Type 47152, produced by G. M. Gian- 
nini and Company. The modulator utilized varicap 
capacitors in parallel with the tuned circuit of 
the modulator oscillator. Voltage from the 
pressure potentiometer, amplified by 20 db to 
put it within the varicap's linear range, was 
inserted across the varicap capacitors. The 
varicap capacitance was proportional to the volt- 
age across it, hence the tuning of the modulator 
was proportional to the 200-cps oscillator's 
input amplitude. 
Deviations in linearity of the pressure 
transducer and the varicap characteristics were 
not sources of error because of the field cal- 
ibration procedure used. During this calibra- 
tion a separate potentiometer which accurately 
simulated the pressure potentiometer was in- 
serted in its place. The potentiometer was hand 
set to simulate various pressure levels, and the 
corresponding 200-cps signal amplitudes were re- 
corded on the tape. The simulating potentio- 
meter accurately duplicated the pressure trans- 
ducer in resistance variation. Precision re- 
sistor steps were used, and the duplication was 
accurate to + 1%. 
The high- and low-pass filters used in 
channel 2 recording were United Transformer 
Company Type HML 12000 and IML 6000. An at- 
tenuator pad was connected to the 600-ohm im- 
pedance level of the 14-db output amplifier. 
This amplifier raised the combined signal level 
up to the necessary O dbm record level. 
Automatic Recovery Mechanism 
The recovery-system mechanism consisted of 
the equipment shown in Fig. 11; this was mounted 
in the afterend of the cylindrical midsection of 
the vehicle (Fig. 12) and in the tail section 
(Fig. 3). When the tail section was mounted in 
place, the heads of four toggle clamps, one of 
which is A (Fig. 11), bore against the top in- 
side of rim A (Fig. 3) of the bouyant tail sec- 
tion, thereby holding the tail tight against the 
midsection (Fig. 12). In the locked-down at- 
titude the levers of the toggle clamps were then 
horizontal and held down, bearing against the 
bottom of disk C. Disk C is an integral part of 
locking unit 0, which is moved downward against 
spring F during loading. The tail was thus held 
securely in place against the midsection by 
means of the four toggle clamps. The locking 
unit O (Fig. 11) was in turn held down by tog- 
gle clamp D, the head of which bore against the 
pottom of slot E of the locking unit 0. This 
required that spring F, sliding with the locking 
