B2-16 PREPARATIONS FOR SOUNDING 
box connections. Also, check for electrical leakage. Use the standby ra- 
diosonde if the instability persists. If an unstable record is received 
from the standby radiosonde, remove the radiosonde from the check box 
and make the baseline-check manually (see JB2-13). 
12.1 Electrical Leakage in the Baseline-Check Box. Moisture or some 
other foreign material in the radiosonde check box test plugs or switching 
unit may cause electrical leakage. When this condition exists, the base- 
line-check temperature ordinate value willbe recorded ata higher value 
than should be indicated. The baseline-check temperature-ordinate re- 
lationship is then incorrect and will result in temperature evaluations 
aloft which are too cold, producing erroneous altitude data computations. 
The test for electrical leakage will be made in accordance with instruc- 
tions issued by the separate services, for the baseline-check box in use. 
13. Manual Baseline-Check. If a baseline-check box is not available, 
or is suspected of producing erroneous results, make the baseline-check 
manually. 
13.1 Preparation for Manual Baseline-Check. Place the radiosonde ona 
desk in the office with exposed thermistor andthe hygristor in line with 
the path of air blown by anearby fan. Maintain as nearly stable conditions 
as possible during the baseline-check. Forced air heating and air con- 
ditioning units should be turned off during the manual baseline-check. 
13.2 Making the Manual Baseline-Check. Use a short wire jumper with 
alligator clips or a dummy connector plug toconnect the black test lead 
to each of the other leads. Make the test connection in the following 
order: 
a. Black to blue (low reference) 
b. Disconnect all test leads (temperature) 
c. Black to red (high reference) or repeat low reference if the 
radiosonde does not have a high reference test lead. 
d. Black to yellow (humidity) 
Allow each circuit to transmit for about fifteen seconds. Repeat the se- 
quence until a satisfactory (see JB2-5.3.1 thru B2-5.3.4) baseline record 
is received. To avoid affecting the radiosonde signal, stand at least six 
feet away from the radiosonde after each test connection. If a stable 
baseline-check is obtained manually, when one could not be obtained with 
the check box, the check box was probably at fault and should be checked 
1-1-69 FMH#3 
