RADIO ACOUSTIC RANGING—ADAMS ° 229 
almost any direction. The hydrophone or the case in which it is housed 
must be watertight. The most frequent cause of hydrophone failure is 
leakage. A hydrophone becomes inoperative if the armature of the 
electromagnetic unit is forced against one of the pole pieces and held 
there. This may result if a bomb explodes too close to the hydrophone 
or if anything strikes the hydrophone while the sono-radio buoy is 
being placed on its station. 
Before a sono-radio buoy is put on station, the gain of its audio 
amplifier must be adjusted for sensitivity. If the gain is too low, the 
unit will be insensitive and returns will not be received from bomb 
explosions more than a short distance away. If the gain is too high, 
the unit will be actuated by the action of the waves, nearby water 
noises, or by the movement of the buoy itself. In the latter case, the 
buoy transmits continuously, and the receipt of a bomb explosion 
cannot be detected. Furthermore, the continuous radio signals inter- 
fere with the receipt of signals from other sono-radio buoys which are 
operating satisfactorily. It is obvious that a sono-radio buoy placed 
on station to operate automatically for several weeks at a time must not 
be adjusted for operation in perfect conditions, for then survey opera- 
tions would often be interrupted by weather conditions. This explains 
one of the principal advantages of a shore station. The latter being 
attended, its sensitivity can be adjusted at all times for best operation. 
Abnormal performance of a sono-radio buoy is usually disclosed in 
one of two ways—either it is too insensitive to bomb explosions or there 
is an excess of stray signals. 
SHIP EQUIPMENT 
The special equipment used on the survey ship for R. A. R. is com- 
paratively simple and easily understood. It consists of a hydrophone 
in the ship’s bottom, a radio receiver, a chronograph and amplifier, and 
a break-circuit chronometer. Except for the chronograph amplifier, 
standard commercial products are used in each case. Their coordinate 
functions from the time a bomb explodes until the radio signals from 
the R. A. R. stations have been recorded on the chronograph are as 
follows: 
The bomb explosion is received on the hydrophone, after which the 
signal is amplified sufficiently to operate the stylus of a chronograph 
which makes a mark on a moving tape. The stylus circuit is then 
immediately connected to the radio receiver. Signals from the R. A. R. 
stations are received and marked on the tape by the same stylus. 
Another stylus operated from a break-circuit chronometer marks regu- 
lar time intervals on the tape during this entire period. Then the time 
intervals from the explosion of the bomb to the reception of the radio 
signals may be measured on the tape. 
