5.0 COBCLOSIOHS 



The airborne man~mfid« radio noiae model ia expected to be representative 

 of almost all large cities, tiew York City r*»ii.g the only known exception. 

 Existing data show that there appears to be a maximum density of man-mad* 

 noise sources, such as automobiles, in a metropolitan area. Continued growth 

 shows a tendency to turn surrounding residential noise areaB to business noiso 

 areas thus increasing the area classified as bu^lnecs. All noise sources used 

 to produce the continental United States nwis-mtide. radio noise maps are assumed 

 to be business areas. 



The airborne radio noise model was developed to cover the frequency range 

 of 30 to 70 MHz and altitudes from 30 to 80 thousand feet. However, the model 

 shows good agreement with scaled Seattle data for altitudes from 5 to BU tuou- 

 sand feet. Further verification of the model must await the collection of 

 data in the frequency range of interest for many different areas. An improve- 

 ment to the model, as indicated in the data of reference 3, would ln± the 

 addition of ground conductivity along the propagation path. In addition, 

 other modes of propagation besides line-of-signt should be considered. 



Examination of figures 9 through 16 shows that very little of the conti- 

 nental United States is free from man-made radio noise during daytime. 

 Because of the height gam, increasing the altituc up to 80 thousand feet 

 does not significantly reduce the noise 2<;vel. Changing frequency in the 30 

 to 70 MHz range has some effect, due mainly to a reductic.i in galactic noise 

 at higher frequencies. It is recommended that to reduce the interference of 

 man-made radio noise on the operation of 4BCS reception of these signals U* 

 carried out, as much as possible, at low altitudes, in rural areas, at night 

 and/or over large bodies of water of at least 100 aules diameter or more. 



19 



