134 



AUSTIN: RADIOTELEGRAPHIC SIGNALS 



apparatus is as follows: A buzzer-driven circuit of fixed induc- 

 tance and capacity has its high frequency current square measured 

 by a sensitive H. & B. hot wire watt meter giving full scale for 

 0.03 watt. To the buzzer-driven circuit is coupled a second cir- 

 cuit with fixed condenser and two fixed inductances tuned to the 

 buzzer circuit. This intermediate circuit is introduced to prevent 

 any direct effect of the buzzer on the detector. To this second 

 circuit is coupled with a fixed coupling a third circuit consisting of 

 a fixed inductance, stopping condenser and the detector to be 

 tested. A Paul microammeter of about 250 ohms resistance, 

 giving two divisions per microampere, is placed around the stop- 

 ping condenser in series with the telephones regularly used with the 

 detector. 2 The plan of the apparatus is shown in the figure, 

 and the value of the inductance and capacities are shown in the 

 table. 



,07 



Hd&^ 



S-Jr 



t 



FsnCiT 



!l-2 



1-3 



J 



:.D 



Fig. 1. Radio-Detector Tester 



B, Ericsson buzzer, 3 ohms. 



>S, 1 or 2 dry cells. 



R, Variable resistance. 



A = 2000 m.3 



Li = L2 = L3 = Li Inductance = 0.4 m.h. 



Ci, Fixed air condenser = 0.0028 m.f. 



C2, Fixed air condenser = 0.0014 m.f. 



W, H. & B. hot wire wattmeter, 6.5 ohms. 



M, Paul Microammeter, 250 ohms. 



T, Telephones 2500 ohms. 



D, Detector under test. 



2 The object of placing the telephones in the circuit is to ensure an approximately 

 normal amount of resistance in series with the detector. 



* Shorter wave lengths do not give enough energy to be measured on the watt- 

 meter without using too much current thru the buzzer contact. 



