226 BELL SYSTEM TECHNICAL JOURNAL 



Beer's Hill reflection, vertical polarization +1.5 decibels 



Beer's Hill reflection, horizontal polarization + 5.1 decibels 



McCatharn Hill reflection, vertical polarization + 0.68 decibel 

 McCatharn Hill reflection, horizontal polarization + 2.76 decibels 

 giving finally: 



Vertical polarization transmission 8.1 decibels below free space 



transmission. 

 Horizontal polarization transmission 2.3 decibels below free space 



transmission. 



Measured Field Values 



The actual field intensity measurements were made using a split 

 half-wave antenna with a transmission line which gave a total loss of 

 about one decibel. Knowing the radiation resistance of antenna and 

 grid circuit input impedance, the transfer voltage ratio could be calcu- 

 lated, and from the grid-to-grid over-all amplification of the receiver 

 the voltage step-up for a given set output determined. The field 

 intensity in microvolts per meter was thus obtained. The measured 

 values were 



Vertical polarization 21.6 microvolts per meter 



Horizontal polarization 38.5 microvolts per meter. 



The transmitter antenna current was 0.05 ampere, and the free space 



field to be expected at 39.2 miles equal to 47.5 microvolts per meter. 



Summarizing the results we have: 



Predicted vertical polarization -f 8.1 db below free space field. 



Measured vertical polarization -f 6.8 db below free space field. 



Predicted horizontal polarization -(- 2.3 db below free space field. 



Measured vertical polarization + 1.8 db below free space field. 

 The measured values are thus within 16 and 6 per cent, respectively, of 

 the calculated values, a satisfactory agreement. 



Appendix IV 

 We have given three methods of field intensity measurement a trial. 

 These are: 



1. Comparison of field intensity with the mean first circuit noise 

 voltage of the receiver. As shown by Johnson ^ the latter can be cal- 

 culated, and by knowing the transfer voltage factor of the antenna- 

 transmission line-input circuit combination and the difference in 

 receiver set amplification for the two voltages the field intensity can be 

 calculated. 



2. Local oscillator comparison.^" Here a local oscillator, with a 



9 Johnson, Phys. Rev., vol. 32, p. 97 (1928). 



'" Described in the Schelleng, Burrows, and Ferrell paper. 



