Since the surface is constantly being 
recorded as well, the depth of bottom features 
below the surface can also be determined from 
the recorder chart. 
When a velocimeter is used with the gear 
its output signal passes through a mixer- 
driver stage in the inverted pinger where it 
is mixed with the receiver signal for trans - 
mission to the surface via the logging cable. 
At the surface the two signals are again 
separated by filters, the velocimeter signal 
being channeled to a counter and printer and 
the depth pulses to a precision graphic record- 
er as indicated above. 
ELECTRONIC DESIGN 
A. The Transmitter 
Fig. 2 is a schematic diagram of the 
transmitter or "'pinger'' circuit. The trans- 
istor power supply consists of two 2N278 
transistors in a multivibrator circuit operat- 
ing at about 800 cycles. The high voltage 
secondary of the multivibrator transformer 
drives a voltage doubling rectifier circuit 
which in turn delivers approximately 1000 
volts to the load. 
The load consists of the two capacitors 
Cj, and Cy in series, which in turn are con- 
nected to the plate and grid circuits of the 
thyratron as shown. When switch SW-1 
closes, the high voltage is applied to the grid 
of the thyratron and the thyratron fires, dis- 
charging capacitors C, and Co through the 
primary of output transformer Tg. To isa 
step-up transformer, the secondary of which 
is tuned to the 12 kc resonant frequency of 
the crystal transducer. A 14 kv, 400 micro- 
second ringing pulse is thus developed across 
this transducer and an acoustic "ping" is 
produced, 
In the first experimental versions of this 
instrument, Switch SW-1 was closed at a one 
second repetition rate by a motor driven cam. 
This motor, governor controlled for precision 
timing, was pre-synchronized to the read- 
out recorder on the ship so as to produce a 
more legible record. However, this timing 
system is not entirely satisfactory and an 
electronic timer of higher accuracy is being 
developed. 
B. Receiver 
Fig. 3 is a schematic diagram of the 
receiver. This unit is fully transistorized and 
comprises three single ended stages fixed 
tuned to 12 kc, a push-pull driver and a 10- 
watt class AB final used as a cable driver. 
The first two stages are designed for low noise. 
The input circuit is somewhat unconven- 
tional and therefore should be explained in 
some detail. 
As indicated in Section A, the transmitter 
develops a 14 kv pulse across the transducer. 
Since this same transducer is used as a re- 
ceiving hydrophone during the listening peri- 
ods, it is essential that the receiver be 
electrically isolated and protected during the 
transmission of the 15,000 volt pulse. It is 
also important that the receiver input imped- 
ance be high compared to that of the 12 ke 
tank circuit formed by the output transformer 
and the crystal transducer. Otherwise, load- 
ing and detuning effects could easily absorb 
most of the power in the transmitter pulse. 
The solution to the problem is shown in 
the receiver diagram. A 15,000 ohm high 
voltage resistor connects the transducer to a 
limiter circuit comprising two 10 watt zener 
diodes back to back. The resistor value is 
high enough to prevent loading the transmitter 
and also limits the zener current to a safe 
value. The zeners clip the receiver input at 
about 4 volts. As this signal would still over- 
load the receiver, a second clipper follows 
the zeners consisting of reversed silicon 
diodes which have a conduction threshhold of 
about 0.3 volt, a reasonable input level. 
C. The Cable 
The oil well logging cable used to support 
the instruments and conduct the signals to the 
surface is essentially conventional in design. 
It consists of an electrical conductor of 
No. 19 stranded copper over which is drawn 
a thin hard layer of extruded nylon. This in- 
sulated center conductor is separated from the 
external sheath by a waterproof soft rubber 
compound which keeps the cable flexible and 
provides additional insulation. 
