INSPECTING AND TESTING THE RADIOSONDE IBS il 
Hz position and value) adjust the ground equipment to the appropriate 
60 Hz value. After the adjustment has been made, turn the INPUT or 
SIGNAL SELECTOR switch to X or SIGNAL and connect the blue to the 
black test lead. After the recorder corrections have been applied, the 
signal should be received at or above 89.0 ordinates but below 100.0 
ordinates. If the radiosonde does not meet this requirement, check the 
test battery voltage or baseline check set internal power supply. If the 
voltage is at or below the lower limit, (see Table B2-1) set the radio- 
sonde aside and repeat the test with the flight battery. If, with the flight 
battery, the radiosonde does not meet this requirement, reject the radio- 
sonde. If the radiosonde is satisfactory, adjust the low reference to 95.0. 
At any station where the power line frequency is suspected of differing 
from 60 Hz, and power line frequency measuring equipment is available, 
e.g., reed-type power frequency meter, determine the power line fre- 
quency to the nearest one-half Hz. With the INPUT or SIGNAL SELEC- 
TOR switch in the 60 Hz position, adjust the ground equipment to the 
appropriate power line frequency. This will be the indicated power line 
frequency divided by 2. 
2.6 Stability Check. While the low reference signal is being received, 
tap the radiosonde lightly. If apermanent shiftof more than 0.2 ordinate 
in the low reference occurs, reject the radiosonde. 
2.7 High Reference. On radiosondes equipped with high reference test 
leads, the red and black leads are shorted together to transmit a high 
reference signal, With the low reference adjusted to 95.0, the high refer- 
ence signal should be received at 96.0 ordinates or above. If it is re- 
ceived below 96.0 ordinates, reject the radiosonde. There are, however, 
some radiosondes where the high reference signal is received at 93.0 
ordinates; with this type of radiosonde, if the high reference signal has 
the same ordinate value as the low reference signal, reject the radio- 
sonde, The primary purpose of the high reference is to facilitate rapid 
identification of contacts. 
2.8 Temperature. If the thermistor is not already installed, install it 
in accordance with JB2-2.5 and 2.5.1. (Ifinstructions for the radiosonde 
in use call for installation of the thermistor just prior to the baseline- 
check, the temperature check will not be done at this time; it will be 
done prior to the baseline-check.) The temperature circuit will be 
checked after the low reference has been adjusted to record at 95.0 
ordinates, After all leads have been disconnected and the pen arm is 
raised from the commutator bar, the radiosonde should transmit a tem- 
perature signal. Using the temperature evaluator appropriate for the 
radiosonde and thermistor being tested, set the ordinate corresponding to 
the temperature signal opposite the temperature of the air at the radio- 
sonde, The 25.0°C line on the evaluator should fall within the limits 
Tal I69 FMH#3 
