INSTRUMENTS AND TECHNIQUES FOR METEOROLOGICAL MEASUREMENTS 
where f is the audio frequency, rt a constant propor- 
tional to the pulse width, b a constant, R the grid- 
circuit resistance, and C the grid-circuit capacity. By 
reducing the pulse width to 65 microseconds and main- 
taining the product bRC constant, r was made quite 
small compared with bRC. Thus, the inverse propor- 
tionality between audio frequency and resistance was 
markedly improved. The accurate evaluation of the 
meteorological data is based upon maintaining a strict 
proportionality between two frequencies for two values 
of R. 
The power requirements for this transmitting unit 
are supplied by a newly developed cuprous chloride- 
magnesium battery, whose capacity and discharge char- 
acteristics are superior to the lead acid cells. When 
required, the battery is actuated by the addition of 
water. Considerable internal heat is generated during 
discharge, hence the usual precautions of thermal in- 
sulation for protection against low ambient tempera- 
ture are unnecessary. A battery pack of sufficient ca- 
pacity to operate the radiosonde for three hours weighs 
less than 600 g. The “A” portion of the battery can 
supply 6.8 v with a 250-ma drain and the ‘‘B” section 
115 v with a 30-ma drain. A comparison of the dis- 
charge characteristics of the lead acid cell and the new 
cuprous chloride-magnesium cell is shown in Fig. 6. 
130 10 
110 8 
ne 
290 6 "my 
> 4," CUPROUS CHLORIDE- 
LEAD ACID MAGNESIUM CELL 
CELL 
“ B" 
{e) ! 2 3 4 
HOURS 
Fie. 6.—A comparison of the discharge curves of the new 
cuprous-chloride magnesium cell and the standard lead acid 
cell. 
The ambient temperature of the cell was changed 
during discharge from room temperature to —58F. 
The radio transmitter represents an important link 
in the radiosonde-radiowind system, for serious errors 
may occur in the meteorological measurements if extra 
precautions in design are not exercised. For example, 
it is necessary to keep the frequency drift of the 1680- 
me oscillator to within a few megacycles in order that 
direction finding should not be impaired. In the present 
design, this drift is maintained in the range of —2 to 
4 me sec. Also, changes in the blocking-oscillator 
rate due to causes other than true changes in the mete- 
orological elements must be kept to a minimum. Audio- 
frequency shifts of 2 cps on release of the radiosonde 
and a gradual change of 2.5 eps during an hour flight 
have been noted. Compensation for these shifts can 
1211 
readily be made in the ground recorder. However, it 
is estimated that random variations in the blocking- 
oscillator rate will introduce probable errors in tempera- 
ture measurement, for example, of about -+-0.2C. These 
newest radiosonde transmitters are quite efficient and 
reliable and represent a real advance in the telemeter- 
ing art. 
Radiosonde Ground Equipment. The ground direc- 
tion-finder shown in Fig. 2 serves the dual role of an 
electronic theodolite [18] and a receptor for radiosonde 
data. These two functions are discharged by the direc- 
tion finder in this manner. The essentially continuous 
waves from the radiosonde transmitter are received by 
the seven-foot parabolic antenna and its scanning sys- 
tem. As indicated in the block diagram of Fig. 1, the 
scanning mechanism places a 30-cps modulation on 
the carrier, the amplitude and phase of the modula- 
tion being a function of the vectorial deviation of the 
target from the axis of the parabola. For radio signals 
arriving along the axis, the amplitude of the modula- 
tion is zero. The modulated carrier is amplified by the 
receiver, detected, and passed through a band-pass 
filter to an electronic commutator which yields a pair of 
d-c voltages, one indicating an elevation error and the 
other an azimuth error. These error voltages are then 
applied to their respective thyratron amplifiers for 
control of the elevation and azimuth drive motors. 
The receiver also detects the pulses that contain the 
meteorological data and passes them along to special 
circuits that amplify and shape the pulses suitably 
for the remote meteorological frequency-meter and 
recorder. 
As an electronic theodolite [18], the direction finder 
measures elevation and azimuth angles as basic data. 
To determine wind speed and direction, it is necessary 
to know either the height of the radiosonde above a 
ground plane or the slant range. In the present sys- 
tem, the height of the radiosonde is computed by 
means of the hydrostatic equation from data obtained 
during flight. Given the height above the ground for 
prescribed time intervals and the corresponding eleva- 
tion and azimuth angles, the horizontal wind velocity 
may be computed by following the standard theodolite 
procedure. 
In analyzing the sources of errors present in wind 
measurement, it is necessary to consider the internal 
precision of angle measurement of the theodolite under 
dynamic conditions, the errors introduced through the 
radio transmitting link, and the errors introduced 
through height determinations. It is estimated that 
the over-all probable error in elevation and azimuth 
angle measurements is 0.05 degrees. This figure takes 
into account random errors due to the swinging of the 
radiosonde, propagation errors, dynamic errors in angle 
measurements at the ground, and errors present in the 
angle recorder. In estimating this error it is assumed 
that the elevation angle is in excess of 6 degrees and 
that a line-of-sight range of approximately 125 miles 
is not exceeded. Tracking accuracy deteriorates rapidly 
for elevation angles less than 6 degrees due to ground 
reflections. For distances in excess of 125 miles, the 
