To use parametric equations (10), (11), and (12) for the calculation of 

 airborne man-made radio noise power the values of integration constants A, h Q f 

 k, B and C must be known. Calculation of these constants requires airborne 

 man-made radio noise data for at least two different altitudes directly above 

 and offset from a business area. 



4.0 AIRBORNE MAN-MADE RADIO NOISE MODEL 



To evaluate how well the above parametric equations describe airborne 

 man-made radio noise, a search tc locate airborne man-made noise data as a 

 function of altitude and distance from a metropolitan area was initiated. The 

 goal was to find data with sufficient detail to allow construction of an air- 

 borne man-made radio noise model valid for altitudes between 30 and 70 thou- 

 sand feet and horizontal distances from the city center out to 300 miles in 

 the frequency range of 30 to 70 MHz. It was felt that a model in this region 

 would be most useful for a KBCS radio noise model. 



An extensive search located only a limited amount of data at frequencies 

 and distances of interest. However, one set of contours was quite complete, 

 showing vertical (0 to 100 thousand feet) and horizontal (0 to 100 miles) 

 values of daytime 1 MHz airborne radio noise power measured and computed 

 for the Seattle area. 3 These contours were replotted by Gierhart, Hubbard and 

 Glen 7 and noise power curves for 30 and 80 thousand foot altitudes were 

 digitized to provide data for the airborne man-made radio noise model. At 

 distances greater than 10f miles, the above curves were extended using the 

 1/R 2 distance dependence exhibited by the near field data at low angles. 



To make use of this 1 MHz data for a radio noise model in the 30-70 MHz 

 frequency range, it was assumed that the curves of reference 7, properly 

 scaled, would be representative of the spatial distribution of man-made radio 

 noise at higher frequencies. Additional Seattle data taken at three other 

 frequencies of interest but at only one altitude and two different horizontal 

 distances, were used to check this assumption. 3 ' 4 ' 6 Table 2 shows airborne 

 vhf radio noise power data at an altitude of 5000 feet for frequencies of 29, 

 49, and 73 MHz compared to corresponding scaled data points from the complete 

 set of data at 1 MHz. 



Frequency (MHz) 



29 



49 



73 



Distance (miles) 



16 



16 



16 



Data (refs 2, 4, 6) 



38.0 28.0 



31.7 22.0 



27.8 17.7 



Scaled 1 MHz data 



39.1 27.2 



31.6 22.0 



26.6 18.6 



Factor 



.596 



.482 



.406 



Table 2. Comparison of radio noise power, F & (dB/'kTb) as 

 a function of frequency for distances of and 16 miles. 



As can be seen, the scaled 1 MHz curve was found to fit the 29 to 73 MHz noi3e 

 data at 5000 feet to within about 1 dB. It was assumed that scaled curves at 

 the higher altitudes of 30 and 80 thousand feet would also fit. 



The scaling factors shown at the bottom of table 2 are used in a Lagrange 

 interpolation formula to scale the 1 MHz noise power data to any frequency in 



