448 



TABLE 461.— F 2 -LAYER CRITICAL FREQUENCIES AND MAXIMUM USABLE 

 FREQUENCIES FOR 4,000-km TRANSMISSION DISTANCE IN Mc (concluded) 



June 



Sept. 



Dec. 



June 



Sept. 



Dec. 



TABLE 462.— FACTORS FOR OBTAINING F 2 -LAYER MUF, AND COMBINED 

 E, F,-LAYER MUF AT OTHER DISTANCES, FROM F 2 -4,000 km MUF AND 



E-2,000 km MUF 



The accompanying table presents (a) factors, F2ooo B - E < F i, by which the 2,000 F-layer 

 maximum usable frequencies may be multiplied in order to obtain values of maximum 

 usable frequencies by combined E- and Fi-layer transmission for other distances, and (b) 

 factors, F t oooF2-F2, by which 4,000-km F 2 -layer maximum usable frequencies may be multi- 

 plied in order to obtain values of F 2 -layer maximum usable frequencies at other trans- 

 mission distances. These factors become less accurate with decreasing transmission 

 distance. 



For obtaining the maximum usable frequency for practical radio transmission, the 

 following procedures may be used : 



1. One-hop transmission: — Obtain both the combined E-, Fi-layer, and F 2 -layer maxi- 

 mum usable frequencies pertinent to the midpoint of the transmission path. The higher of 

 the two will be the MUF for the path, neglecting possible transmission by sporadic -E 

 ionization. 



2. Long-path transmission: — For transmission paths exceeding 4,000 km, the following 

 procedure generally affords a sufficiently good value for practical use: 



(a) Determine the 2,000-km F-layer MUF for a point 1,000 km along the transmission 

 path from the transmitting station. Determine the 4,000-km F 2 -layer MUF for a point 

 2,000 km along the transmission path from the transmitting station. Select the higher of 

 two values, for comparison with a value to be later obtained in procedure (b). 



(b) Determine the 2,000-km F-layer MUF for a point 1,000 km along the transmission 

 path from the receiving station. Determine the 4,000-km F 2 -layer MUF for a point 2,000 

 km along the transmission path from the receiving station. Select the higher of these 

 two values, for comparison with the value obtained in procedure (a). 



(c) Compare the values obtained in procedures (a) and (b) above. The lower of the 

 two will be the MUF for the transmission path, neglecting possible transmission by 

 sporadic-F ionization. 



For more detailed and accurate procedures, and for inclusion of sporadic-F layer effects, 

 reference is given to National Bureau of Standards Circular 462, "Ionospheric Radio 

 Propagation," and to reports of the Central Radio Propagation Laboratory, Series D, 

 "Basic Radio Propagation Prediction." 



SMITHSONIAN PHYSICAL TABLES 



