METEOROLOGICAL EQUIPMENT FOR PROPAGATION STUDIES 



99 



SONDE 

 ELEMENTS 



R H, 



CABLE 



0-50 

 MICROAMP 



I.S V 



T 

 METE 



(7) 0-50 





MOTOR 

 60 R PVI 



\k 



r 



RELAY 



6 V DC 



Figure L Wired sonde circuit. 



The potentiometei- P applies a constant voltage (0.3B v at low and 0.18 v at high HH) to both of the independent circuits of the sonde proper. 

 The currents, determined by the resistances of the relative humidity and temperature elements respectively, are read on the RH meter and 

 T meter. S3 commutates these currents at half-second intervals: Si and -S2, actuated simultaneously with 53. maintain constant polarity at the 

 meters. The l,000-;if condensers CC smooth the currents through the meters. S1S2S3 are contained in the pile-up of a single relay which is actuated 

 by a miniature worm-geared motor as shown. The 10,000-ohm protective resistance R is shorted out during measurement. Connections to the 

 ground end of the cable are made through slip rings (not shown) mounted on tlie cable reel. All components, excepting the sonde, cable, and 

 6-v storage battery, are housed in a single case 20.x9x7 in. 



but is short euoiigli to allow of smoothing the curreuts 

 through the meters. 



Tlie circuit illustrated in Figure 2 has been devel- 

 oped by the Propagation Groirp at the Radiation Labo- 

 ratory, MIT.* The apparatus includes two Sanborn 

 resistance elements, one of them surrounded by a mois- 

 tened wick. The current flowing through the resistors 

 originally was fed into an amplifier which drove a 

 recording milliammeter. However, after a number of 

 amplifiers had been tried, the simple scheme shown in 

 Figure 2 was adopted and, at the time of the writing 

 of this report, is being used for all measurements made 

 by the Radiation Laboratory, those from planes as 

 well as those from captive balloons which will be 

 described later. 



The dry and wet elements are placed in the circuit 

 alternately by means of a hand-operated switch. The 

 device can be calibrated by means of a set of fixed 



precision resistors and the balance of the bridge is 

 checked before each flight. An advantage of this 

 method is the possibility of using a commercial d-c 

 recorder (0 to 1 ma) immediately at the plate ter- 

 minals of the amplifier tube. This is particularly 

 favorable for use in airplanes and dirigibles. 



It is well known that the ordinary thermocouple is 

 not readily adapted to recording purposes. Only at sta- 

 tionary installations such as towers, where multi- 

 junction thermopiles can be used, is it possible to 

 record the indication of the sensitive galvanometers 

 required. 



^■^•^ Anemometers 



Wind measurements are of importance iu connec- 

 tion with off-shore winds at coasts which give rise to 

 pronounced refraction of short and microwaves. The 

 ordinary commercial anemometers become quite un- 



