TROPOSPHERIC PROPAGATION AND RADIO METEOROLOGY 
free space while the fluctuations varied between 10.5 
db above to more than 30 db below free space. The 
level was 5 db or more below the undisturbed value 
during 0.01 per cent of the time in January and 
during 0.4 per cent of the time in July. On the 2,800- 
me circuit the undisturbed level was —2 db below 
free space; the maximum was 12 db above and the 
minimum more than 25 db below free space. During 
0.15 per cent of the time the signal was 5 db or more 
below the undisturbed level in January; the corre- 
sponding figure for July was 3.6 per cent. The conclu- 
sion may be drawn from this and similar experiments 
that over optical paths transmission becomes gradu- 
100 
Be ee ee a TET 
ne ee 
envi aaa Re PA esl 
(eee iS A en al 
ils Ba oe SI 
DED ae hy) 7 Ee ee 
ee AAR een 
10 —O— 474 MC HAUPPAUGE can Cee ce 2d a eee er 
< —X— 2800 Mc HAUPPAUGE iano Gal meet amas Sore 
3 +TO=— 45.1 MG RIVERHEAD Racha a7 a [| | 
2 -—X—- 474 MC RIVERHEAD | OPTICAL Fan ere aah eae 
= En ee aa ae 
| (See [eT] eA I ne 72] Re 
5 UC ae Pie Ee a ae oa (Sa AT A 
2 AE el i es a ee 
2 | RS ae a Se 
= 1.0 _—— a SS S=  — S 
) San Ree Re ny |e Gey a a DE Sl 
rr) (Scr?) ee PS Pa ae ET Al ay A eT ey (ay | ET a ae 
[aE Ee (ya By A SS ae 
vi i eo Ee HATS) al 
: rere fv =| nae ee 
f z ee el 
a @ 
= a 
: Zen 
(=) 
i 3 
0.! 
01 
-20 “15 al 
163 
ally less reliable as the frequency is raised. 
Over the nonoptical path, New York to Riverhead, 
the margin of fluctuations was much larger. On the 
45-me circuit the undisturbed value was 35 db below 
free space, the maximum 18 db below, and the 
minimum more than 50 db below free space. During 
1.6 per cent of the time the signal was 5 db or more 
below the undisturbed level. On the 474-me circuit 
the undisturbed signal was 30 to 35 db below free 
space, the maximum 10 db above, and the minimum 
44 db below free space. During 0.47 per cent of the 
time the signal was 5 db or more below the undis- 
turbed value. At 2,800 me the undisturbed signal 
= as 
Oo 5 10 
RELATIVE SIGNAL STRENGTH IN DB 
Figure 38. Reliability of circuit. Average of July 1943 and January 1944. (Empire State Building to Hauppauge and 
Riverhead, L. I., N. Y.) 
