262 



HI-:LL SYSTh.M TECHNICAL JOCRXAL 



Hague Conference of the C.C.I.R. has recommended it as a principle. 

 The carrying of it out in practice means that, in general, communica- 

 tions over the shorter distances should be carried out on the lower of 

 the high frequencies (and possibly at the extreme high frequencies). 

 It logically calls, also, for making the maximum use of existing wire 

 networks for overland services, in order to free the radio channels for 

 uses for which they are most needed. Finally, there is, of course, the 

 need for coordinating the transoceanic links among themselves and 

 minimizing unnecessary duplication. 



In the Washington, 1927, Convention the world took a construc- 

 tive step forward in organizing the use of radio channels by blocking 

 out the high-frequency spectrum in respect to classes of service, thus: 



aooo 



DISTANCE -STATUTE MILES 



Fig. 11 — ^Frequency-distance characteristic. 



point-to-point, relay broadcast, mobile services. It is of interest to 

 note that there is a further line of distinction which might be availed 

 of for the purpose of reducing interference. As matters now stand, 

 powerful and expensive stations which can well afford to live up to 

 the highest standard of frequency stability, radio receiver selectivity, 

 etc., are intermi.\ed in the frequency spectrum with stations which 

 cannot justify living up to these standards. Wide differences, in the 

 caliber of station in accordance with the different needs is, of course, 

 to be expected. This would appear to call for some grouping of sta- 

 tions in the various frequency bands in accordance with the frequency 

 tolerance which they are prepared to meet. Some indication of the 

 prevalence of interference on these short waves is given by the experi- 

 ence which has been had in operating the transatlantic short-wave 

 telephone circuits during the lirst six months of 1930. Of some 3,000 

 operating hours in which the short-wave circuits were commercially 



