31 8 hull: transmitter op modulated waves 



watts in an antenna having 8 to 15 ohms resistance and a natural 

 wave-length below 200 meters; (3) a readily adjustable range of 

 wave-lengths from 500 to 1000 meters; (4) transmission of com- 

 pletely modulated waves, making possible their reception with 

 crystal detectors; (5) sharply tuned waves, in order to avoid 

 excessive interference over long series of tests. The set has been 

 used in fog signaling and direction finding experiments, and in 

 transmission tests carried out as part of an investigation of 

 wave propagation. 



In designing the set the average power output in a given 

 antenna was taken as the criterion of its merit as a transmitter 

 of radio waves. The kind and degree of modulation of the waves 

 radiated determine to a large extent what type of receiving cir- 

 cuits should be employed to utilize this power effectively. How- 

 ever, if it be understood that an appropriate receiving circuit 

 is to be used, the effective current output in an antenna of given 

 radiation resistance at a given wave-length determines the merit 

 of any transmitter of modulated or unmodulated waves. 



Figure i is a diagram of connection of the final form of this 

 transmitter as put into service for radio direction finding and 

 fog signaling. 



Owing to the fact that the 500-cycle voltage, when using a 

 2 kw. alternator, dropped enough to decrease the filament cur- 

 rent by as much as 15 per cent when the load was thrown on in the 

 plate circuit, it was found necessary to include in the filament 

 transformer a series compensating winding. This is rendered 

 doubly imperative by the fact that when operating a tube at 

 high plate voltage, the power output changes to a much greater 

 extent with slight changes in emission than when operating at 

 lower plate voltages. The system is always kept adjusted for 

 maximum output at the maximum safe filament current, /, 

 effective = 3.6 amperes, and even a slight decrease in this cur- 

 rent decreases the power output considerably, and the current 

 output to a corresponding extent. In order to be able to adjust 

 this transformer to give suitable compensation for the drop in 

 primary voltage, and still be able to use it at different values of 

 generator voltage, when it is found desirable to transmit at 



