1020 millibars) against. percentage of the turns
as read on the nomogram. The lowest pressure
reading is numbered as read and succeeding
pressures are plotted in a continuous ascending
series. When the pressure reading reached the
first_overlap on the reference, it is called
100 percent; the second overlap is 200 percent
and so on until the last overlap which may be
1200 or 1300 percent.
(c) Pack the modulator and insert it inside the
transmitter box. The modulator should be pro-
tected from extreme cold since the motor opera-
tion becomes erratic when the temperature reached
:soo to 400C below zero. A box or paper cover
over the modulator will keep particles of in-
sulation and dirt from the moving parts.
(d) When the entire assembly has been made and in-
flation of the balloon is about to begin, the
transmitter and motor should be turned on and
reception of the signal tested. If any serious
trouble appears, the modulator should be re-
placed by another calibrated modulator since
any work on the instrument will probably change
the calibration.
During the flight,radio static and noise will
appear on the Brush record as pips which may re-
semble the transmitted signals and with increasing
distance or weakening transmitter the noise will
finally completely obscure the pressure record.
Careful tuning of the receiver will prolong
the record as long as possible. When tuning
the receiver, the sensitivity control of the
Brush amplifier should be turned to the least sen-
sitive position since any sudden change in the
tuning may throw the pen off its supports and
damage its glass tip.
'When the flight reception is completed the re-
cord is evaluated exactly as in the evaluation
of the calibration record--using the same nomo-
gram. However, since the instrument is subjected
to different atmospheric condition~, the motor
speed may vary suddenly, giving false values for
the pressure. These values may be detected by
carefully observing the rate of rotation of the
motor, which is measurable by the distance be-
tween the reference marks. If there is a sudden
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