26 TECHNICAL SURVEY 
U 2 3 4°75 6 7 8 92 wo WI 12 03 I@ 1S 16 (7 W 19 20 21 22 23 24 25 26 27 28 28 BW 
a rE 
FFD, FAS a 
1 a 
ey ON A 
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0 LA 
7 oon te 
|, 
1G iecwor la OMeNLU Les Co neetdam a WECM CA 
‘ 2 3 4 5s 66 vO 9 10 2 
ot a Ne ot at oa eit oa 
Ao Nt “ae 
B aerate r WHR J Tracey 
1314 «15 
een 
YT YE Vsranonno [4 WV | 
Figure 1. Signal strength in decibels above 1 uv receiver input. S band hourly means, June 1944. (Irish Sea experiment.) 
(C = cold front, W = warm front, O = occluded front.) 
fronts, are shown at the top of the diagram. W indi- 
sates warm, C cold, O occluded. Note in particular 
the standard and the free space level indicated on 
the lower record and the ‘free space level on the 
upper. The standard level for the latter would be 
about 33 db below the zero line. This record, which 
is by no means exceptional, gives a fair idea of how 
vastly the signal exceeds the magnitude calculated 
for standard conditions. At the same time it shows 
the highly irregular character of these phenomena 
and the difficulty of correlating them in a simple 
way with the weather or other conditions. 
OVERLAND PaTH 
An experimental overland path 38 miles has long 
been operated in the neighborhcod ‘of London between 
the Admiralty Signal Establishment at Whitwell 
Hatch and the General Electric Laboratories at 
Wembley. The wavelength is in the 10-cm band, 
and transmission, monitoring, frequency control, and 
recording are fully automatic. The path is optical 
except for some houses and trees near the receiver 
30,16. 17, 18, 19 | 20,21 , 22, 23 Tea 
Figure 2. Whitwell Hatch-Wembley path, March 1944. 
S band hourly mean intensities in decibels above 1 pv 
receiver input. 
which introduce a diffraction loss estimated at 30 
db. As is generally the case with paths that are 
optical or nearly so, the fluctuations of received 
intensity are far less than in the case of long non- 
optical paths. Figure 2 shows a record for one month 
in 1944. The large diurnal fluctuations in amplitude 
with maxima above normal in the early morning 
hours occur in the beginning of the month and at 
several occasions later, especially from the 21st to 
the 26th. These are related to weather conditions 
with clear skies, as will be explained in Chapter 4. 
The work undertaken in England on experimente] 
transmission paths of various types is quite extensive, 
and the preceding description hardly gives an idea 
of the variety of experiments made and results 
obtained. Most of the experiments are of a smaller 
size than the ones described here. 
EXPERIMENTS AT THE EASTERN 
COAST OF THE U.S. 
In the early years of the war a transmission 
experiment was undertaken by RCA Communica- 
tions, Inc., between New York and two points on 
Long Island.13!% The short path of 42 miles was 
optical, but the long path of 70 miles was nonoptical, 
the receiver being about 400 ft below the trans- 
mitter’s line of sight calculated on a 4% earth’s radius 
basis. Transmission was carried out on 45, 475, and 
2,800 me. The results show what has been confirmed 
by later experiments, that the amplitude of fluctua- 
tions is larger the higher the frequency. On the 
optical path the range of fluctuations of the 45-me 
signal averages only +3 db, whereas over the same 
path the 475-me and 2,800-me signals exhibited 
fluctuations which were in excess of 40 db, so far as 
they could be measured. As was to be expected, the 
2,800-me signal fluctuated more than the 475-me 
one. Over the nonoptical path all three signals show 
