AUSTIN: RADIOTELEGRAPHIC SIGNALS 135 



It will be seen that this detector tester differs from others in 

 that the wave lengths, inductances, couphng, etc., are fixed 

 and the test becomes simply the measm-ement of the response of 

 the detector to a definite amount of high frequency excitation. 



The sensitiveness of the detector is determined by observing 

 the deflection on the microammeter corresponding to a reading 

 of 0.005 watt on the wattmeter in the buzzer circuit. The ratio 

 of wattmeter to microammeter reading may be expressed in terms 

 of energy requii-ed to produce a response, arbitrarily taken as the 

 least audible signal under average conditions. This energy cali- 

 bration of the detector tester is made once for all by means of a 

 detector calibrated immediately before by the thermoelement 

 and galvanometer method. 



For example, a certain detector, which by the method already 

 mentioned^ has been shown to require 3.1 X 10"^ watts to pro- 

 duce an audible sound in our standard laboratory telephones, 

 produces when placed in the tester a deflection of ten divisions on 

 the microammeter for a reading of 0.005 watt on the buzzer cir- 

 cuit wattmeter. Now, if some other detector be placed in the 

 tester and gives five divisions for the same wattmeter reading, 

 it is half as sensitive as the first and requires 6.2 X 10"^ watts 

 for audibility in the standard telephones. 



Experience has shown that the amount of energy required to 

 produce a certain strength of signal from the detector is indepen- 

 dent of the wave length and approximately independent of the 

 spark frequency.^ It has also been found that, when the detector 

 circuit is coupled to the antenna just closely enough to produce 

 maximum strength of signal, the energy is equally divided between 

 the antenna and the detector circuit.^ From this it follows that, 

 if we know the energ}^ in the detector, we have a measure of the 

 received energy and, if the total resistance of the antenna, includ- 

 ing that introduced by the coupled detector circuit be known, and 

 the effective height of the antenna be also known, ^ from the 



^ Bulletin, Bureau of Standards, 7: 295. 1911. 



5 Entirely so for galvanometer deflection. 



6 Bulletin, Bureau of Standards 7: 301, 1911. 



^T. Ruedenberg, Ann. d. Phys. 25: 446. 1908. Journal of the Washington 

 Academy, 1: 275. 1911. 



