vier RADIOSONDE INSTRUMENTS 
are provided with the thermistor mounted externally on an outrigger 
which exposes it at some distance from the radiosonde case. The hy- 
gristor is enclosed within an airduct to shield the element from direct 
exposure to precipitation. The radiosonde contains an aneroid baroswitch 
for measuring pressure, a white- coated thermistor for temperature, and 
a carbon hygristor for relative humidity. Radiosondes of this type will 
be considered the basic radiosonde and will usually be identified by a 
serial number containing no suffix. 
1.1 Serial Numbers of Radiosondes Differing From the Basic Radio- 
sonde, Serial numbers are used to identify radiosondes differing from 
the basic radiosonde. The following isalistof the suffixes used to iden- 
tify these radiosondes. 
a. Radiosondes for use with high-altitude balloons are equipped 
with hypsometers to provide more accurate measurements of 
pressure than that provided by the aneroid cell at very high 
altitudes. These radiosondes will usually be identified by the 
letter '"'H'' appended as a suffix to the serial number. 
b. Radiosondes for use with the transponder system are equipped 
with a receiver to intercept the ranging signal radiated from 
the transponder ground adjuncts. These radiosondes will usu- 
ally be identified by the letter ''R' appendedas a suffix to the 
serial number. 
c. Radiosondes equipped with both the hypsometer and the trans- 
ponder capability will usually be identified by the letters "HR" 
appended as a suffix to the serial number. 
d. (WB) Reconditioned radiosondes are identified similarly ex- 
cept an additional letter is placed aheadof the serial number, 
ate Radiosonde Frequency. Radiosondes currently in use by U.S. Sup- 
ported Upper-Air Stations and Ships operate on a nominal carrier fre- 
quency of 1680 or 403 MHz. These frequencies are used as follows: 
a. The 1680 MHz radiosonde transmits a 100 percent amplitude 
modulated signal at a nominal frequency of 1680 MHz. The 
frequency modulated 403 MHz radiosonde transmits a signal at 
a nominal frequency of 403 MHz. The transmitted signals of 
these radiosondes provide meteorological data and serve as 
the direction- finding or tracking signal for the rawin receptor. 
i= Oe) F MH#3 
