TRANSATLANTIC RADIO TELEPHONY 



135 



10 minutes of disconnected spoken words. 



10 minutes of a succession of five-second tone dashes separated by 

 five-second intervals, (for measurement of the received field strength, 

 the intervals between the dashes being used for throwing on the local 

 receiving source and adjusting its strength to equal that of the receive 

 signals by alternately listening to one and then the other). 



Transatlantic Radio Transmission Measurements 



Diurnal Signal & Noise Variation 



Jenl-Febr23, 1923. 



12 M I 2 5 4 5 6 7 6 9 10 11 12 1 2 3 A 5 6 7 8 9 10 11 \2j A 

 78 910 11I2M1 2 3 456789 10 11 12 1 2 5 4567 



■ New York Tun e ^ ^^— — ^^^^^^^^^1W 



Fig. 9 



Immediately following this test period the London observers 

 measured the noise level. 



This unit test period was repeated every hour over a period which 

 varied from several hours to as long as two days' duration. Most of 

 the test periods ran for about 28 hours, starting about eleven o'clock 

 Sunday morning and continuing until about three o'clock Monday 

 morning, London time. During this time the telegraph load through 



