hull: transmitter of modulated waves 321 



gave a power output in the antenna of 286 watts, at 600 meters 

 wave-length, using an effective value of filament current of 3.5 

 amperes, and operating at an overall efficiency of 35 per cent, 

 alternator terminals to antenna inclusive. This efficiency takes 

 account of the power expended in the filament supply trans- 

 former and in the filament. No data are available on the effi- 

 ciency of the tube alone, as ordinarily computed in terms of 

 input to the plate and output in the antenna. It was impossible 

 to adjust the coupling so as to obtain maximum output at the 

 shorter wave-lengths. 



TRANSMISSION AND RECEPTION TESTS 



Signals from this set, which suppHed 5 amperes effective 

 current to an antenna approximately 50 feet high in Washington 

 were copied at a distance of 100 miles by using an antenna 60 

 feet high, with an audibility of 10,000, using an autodyne re- 

 ceiving circuit with a two-step audio-frequency amplifier. Sig- 

 nals from this set working under the same conditions were re- 

 ceived through heavy interference by using a six-foot coil aerial 

 and a similar detector and amplifier, at a distance of 225 miles. 



It has been found in other tests that waves modulated in this 

 fashion cannot be received with high efficiency with a simple 

 non-oscillating detector. The voltages induced in a receiving 

 antenna by a logarithmically modulated wave will give a re- 

 sponse on the output side of the detector greater than that in- 

 duced by a sinusoidally modulated wave train radiated from 

 antennas in which the effective antenna current is the same, 

 provided always that we confine our attention to short wave- 

 lengths. The truth of this statement has been proven experi- 

 mentally by direct comparison of two such transmitters. It is 

 beyond the scope of the present paper to discuss quantitatively 

 the effects of sinusoidally and logarithmically modulated wave- 

 trains upon receiving antenna with rectifier and phones. How- 

 ever, a possible reason for such a behavior is suggested by the 

 accompanying diagram, figure 2, upon which are plotted to 

 the same scale the envelopes of spark and sinusoidally modulated 

 wave trains emitted by two transmitters operating at 500 cycles 



