198 BELL SYSTEM TECHNICAL JOURNAL 



ceivers and constructed several different types of these. All the 

 quantitative data, however, were obtained with a measuring set 

 employing a double detection receiver. 



This receiver is of much the sarrie type as the one described by Friis 

 and Bruce,^ the modifications in the short-wave circuits necessary 

 to reach the ultra-short-wave range being obvious if not exactly easy 

 to carry out. The intermediate frequency is 1300 kilocycles; there are 

 five amplifier stages preceded by a double tube short-wave detector and 

 followed by a single tube low-frequency detector. The band width 

 (6 decibels down) is approximately 80 kilocycles, and the over-all gain 

 103 decibels. The amplifier tubes are shielded grid type, and the 

 beating oscillator input is introduced, balanced, in the first detector 

 grid-filament connection. The ultra-short-wave tuning circuits have 

 commercial micrometer heads clamped to the condenser dials. This 

 has proved to be a satisfactory type of vernier adjustment. The 

 shielding extends to the individual tubes and coupling circuits and is 

 complete and thorough. By-pass filters to ground are on all the power 

 input connections. The range is 3.7 to 12 meters using several sets of 

 coils. Two photographs of this receiver are given in Figs, la and lb. 

 For some of this work a manually operated gain recorder was fastened 

 on the set base, with operating pen belted to the set attenuator handle. 

 This recorder is a remodeled sample of the type 289 General Radio 

 fading recorder. 



Experimental, Preliminary 



The first ultra-short-wave receptions, made in September, 1930, with 

 the superregenerative receiver, showed that a cross-country transit 

 was accompanied by marked variations in field intensity over even 

 rather short distances (one meter for example) . Locations were readily 

 found where the reception was very weak, usually areas, as gullies, 

 below the average land level. Hilltop reception was uniformly good 

 and a range of 50 miles (80.5 kilometers) was attained on the third 

 trip. At this site (Musconetcong Mountain, N. J.) the reception, weak 

 at the ground level, was greatly improved by carrying the receiver to 

 the top of an airplane beacon tower. A 75-mile (120.8-kilometer) re- 

 ception at the Pocono Mountains in Pennsylvania failed, the path 

 being unfavorable for the amount of power available at the trans- 

 mitter. There was ample indication that straight-line or "optical" 

 transmission was not the only possibility, and there were indications 

 that both earth-reflected and earth-diffracted radiations were present. 

 No fading and no static were noticed. Later trips added little of sig- 



^Proc. L R. E., vol. 14, p. 507 (1926). 



