MOBILE RADIO TRANSMISSION 1085 



These data bring out another interesting and significant fact. Where 

 noise collected i)y a dipole anteiuia is discernible over set noise, the noise 

 collected by the 7 db gain antenna at the same site is, surprisingly, less. 

 This means that the gain antenna picks up less noise power than a dipole. 

 Since it picks up 7 db more signal from a distant car, a gain antenna 

 thus provides a double impro\'ement in liaiismission at those sites for 

 which ambient noise is controlling. 



An explanation of this behavior maj' l)e surmised if it is assumed that 

 the sources of noise are numerous and are scattered around at street le\'el 

 (motor vehicles, mostly). The overall noise received is a sum of contri- 

 Initions from all sources, weighted for distance and the receiving antenna 

 pattern. A gain antenna of the type considered here tends to ignore the 

 strong nearb}^ noise sources because they are below the antenna beam. 

 The sources, which are nearly enough in the beam to count, are also 

 further away and are attenuated by distance. 



The amount of data given in Table I does not seem sufficient to war- 

 rant stating a firm figure as to the amount of improvement obtainable 

 from a gain antenna. However, substantial improvement at 150 mc is 

 indicated, and this might have the effect of bringing the value of mobile 

 transmitter power required at 150 mc down to the value required at 

 450 mc, assuming gain antennas in both cases. 



ACKNOWLEDGMENTS 



A number of people participated at one time or another in setting up 

 and carrying through these tests. It is not possible to name them all, 

 but the principal participants were R. L. Robbins, R. C. Shaw, W. 

 Strack, D. K. White, and F. J. Henneberg. The program was supervised 

 b}^ D. jMitchell. The special radio equipment required was designed and 

 furnished by W. E. Reichle and his group. 



