492 BELL SYSTEM TECHNICAL JOURNAL 



to the transmitter tube grids. The transmitter grids thus received a 

 voltage pulse each time that the transmitter frequency passed through 

 one megacycle above or below the beating oscillator frequency. Each 

 transmitter frequency sweep was thus marked with two pulses spaced 

 two megacycles apart. 



The second transmitter had Lecher wire tuning elements, covered 

 the wave-length range of 3.5 to 1.2 meters and had a power output of 

 30 watts at 1.5 meters. It was in operation simultaneously with the 

 first transmitter for six months and then was replaced by transmitter 

 No. 3. 



The third transmitter was coil tuned, covered the wave-length range 

 of 4.9 to 2.8 meters and had a power output over this range of 55 watts 

 down to 35 watts. It was operated simultaneously with the first 

 transmitter except for the first six months. 



All three transmitters were arranged for voice modulation through a 

 simple grid input, and the first one was thus used for one-way com- 

 munication during the entire period of operation. 



Normally, unmodulated waves were transmitted and were observed 

 as rectified direct current in the output of the double detection re- 

 ceivers. These receivers had attenuators, variable in steps of 1 db, 

 in the intermediate frequency amplifier circuits and the attenuators 

 were geared to the pens of manual recorders. The operators kept the 

 output current constant by means of the attenuators just mentioned, 

 and there resulted a record of signal amplitude versus time. Some use 

 was made of the Esterline-Angus type of milliampere recorder for 

 automatic recording but no linear scale recorder of this type could 

 handle the amplitude range of the fading encountered. 



For the reception of the frequency modulated transmission a tuned 

 radio-frequency receiver, with a three-megacycle band-width centered 

 on 66 megacycles (4.55 meters), was constructed and its rectified output 

 was applied to one pair of plates of a cathode ray oscillograph. A 

 linear sweep voltage, manually synchronized with the transmitter 

 60-cycle power voltage, was applied to the second pair of plates. The 

 oscillograph pattern thus pictured the frequency-amplitude charac- 

 teristic of the radio circuit in toto. Over the frequency range where 

 the receiver band was flat (two megacycles) the curve gave the ap- 

 parent ether characteristic. With a motion picture camera this 

 characteristic was permanently recorded. 



Fading Characteristics, General 



The fading was always slow compared with that observed on short 

 waves. Except for the rapid fluctuations produced by airplane reflec- 



