Calculation of surface noiae power can now betjin with selection of the fre- 

 quency aad the determination of the three coefficients of equation (1). Sub- 

 stitution of the coefficient values into equation (1) and setting k equal to 

 2.5 miles allows the calculation of surface noise power as a tunction of dis- 

 tance. 



Figure 4 shows the surface noise power function, p , in units of power, 

 watts per bandwidth, graphed as a function oc distance from the center of a 

 business area for 30, 50 and 70 Kilz. 



-» h 



8 5 18 13 



DISTANCE <HRES> 



Figure 4. Surface man-made radio noise power, in watts per 



bandwidth, calculated for 30, 50, and 70 MHz, and plotted 



as a function of distance from the center ot a business area. 



3.0 AIR30FNS MAH-KADB RADIO NOISE 



Airborne man-made radio noise measurements have been made above many 

 American cities at various altitudes in the frequency range from 1 MHz to 1 

 GHz. Measurements using forward-directed an^.ennas have detected man-made 

 radio noise ir. excess of 200 miles from large cities. They indicate that air- 

 borne man-made ladio noisa from a distant metropolitan area can be detected 

 once the airciaft rises above the local optical horizon. At high altitudes, 

 above ^0,000 feet, measurements made with a low-directivity antenna show a 

 broad noise signature that is representative of the entire metropolitan area. 

 Measurements nusdft L-elow 10.000 feet with a high-directivity antenna show more 

 detail of local noin-a sourceo dve to the smaller surface area subtended by the 

 antenr.s oattern. 



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