B1-10 INSPECTING AND TESTING THE RADIOSONDE 
1, Radio-Frequency (see §B1-2.3) 
2. Radiosonde Signal (see §B1-2.4) 
3. Low Reference (see §B1-2.5) 
4. Stability Check (see JB1-2.6) 
5. High Reference (see §B1-2.7) 
6. Temperature (see §B1-2.8) 
7. Hypsometer (see JB1-2.9) 
8. Humidity (see §B1-2.10) 
9. Relay Defects (see §B1-2.11) 
2.3  Radio-Frequency (r-f). Check and adjust the r-f of the 1680 MHz 
radiosonde to within +2 MHz of 1680 MHz. Check and adjust the fre- 
quency of the 403 MHz radiosonde to within +1 MHz (N, +2 MHz) of 
402.5 MHz. In order to preclude the possibility of erroneous bearings, 
and fading or unstable signals, the frequency of the radiosonde used for 
a second release should also be adjusted to the frequency specified 
whenever the wind speed and direction are such that interference will 
not result from the first radiosonde released. Duringa period of light or 
uniform winds, when there is a strong likelihood that the second radio- 
sonde will be in a direct line with the first, thereby causing serious 
interference, the r-f of the second instrument should be adjusted to 
either 401.5 MHz, or 1675 MHz. - 
2.4  Radiosonde Signal.Tune in the radiosonde signal in accordance with 
instructions for the receiver used. Check to determine that the contact 
point is raised from the commutator. If a signal is not received, check 
that the receiver is operating and that all tuning controls and switches 
are properly adjusted. If the trouble is not found, test by connecting the 
red or blue test lead to the black test lead. If a signal is not now re- 
ceived, reject the radiosonde. If several successive radiosondes are 
rejected under these circumstances, suspect trouble with the ground 
equipment. If a radiosonde with a separate transmitter is used and a r-f 
signal is received but not an audio signal, replace the radiosonde trans- 
mitter and retest. 
2.5 Low Reference. With the INPUT or SIGNAL SELECTOR switch in 
the 60 Hz position (if ground equipment has no 60 Hz position, use the 120 
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