CALCULATION OF RADIO GAIN 
411 
wes 
Ne 
MNAL | 
AKAAL | 
ASS 
Sa 
NE 
\ 
\\ 
\ 
S 
 \ 
x 
Nae 
‘ 
VAT AA SAAS 
‘ 
IN 
MN 
. 
INN 
\ 
ANA 
| | VA\M\A 
FEN 
sag 
o Gases he 
oceans Be 
ef Aoi SS es a 
(Jae ae 
AEDZesEeeser 
120 Ese eee s 
100 Bees e eee se 
\eseeeeeeese 
eee ee 
(22222 a 
eee ia 
eae isl 
G 
16 17 18 19 
Coors 
Sear 
ene: 
meee 
(eae 
Zo sd or sy! 
TicureE 38. eh2 = eu versus sd = sv. 
3 
BOTH ANTENNAS LOW nt <30)" 
2 
20109 A= 20 log A-20 log h, 
Figure 39. ehz = eu versus sd = sp. 
elevation at the distance d is lowered in changing 
from 4a/3 to ka. At this distance the height of the 
line of sight is hy, and 
Jig a aw (an 2p) es) 
a 
83 
becomes 
[de d My 
Vie == = Vi 166 
f V2ka i ee) 
so that there is a downward shift of approximately 
3a ( 4 ) Eee ( 2) 
figs pegien eee (in aes a A Teale \. 
ma Mersil, 8G 3h) ~ 2VaNg, 3k 
(167) 
If h, 1s small compared with hz, and hz’, the result is 
approximately 
4 
Bee ee eA 
eee i 1 a ) 
Receivers situated between hz and hz’ were formerly 
below the line of sight but are now above it (assum- 
ing k > 4/3), with a consequent substantial gain in 
signal stréngth at some points and loss at others. 
The chances of detection in the region, however, have 
improved. 
If both antennas are low, a change of 4a/3 to ka 
gives a field strength change such that the field 
which was formerly at a point d well within the 
diffraction region will now-be found at a distance of 
appr oximately 
3 k 2/3 
( ) 
4 
except for the decrease in free-space gain (20/3) log 
3k/4, occasioned by the increase in distance. If, for 
instance, k = 12, the free-space gain is equal 
approximately to —7 db, and the ratio of the new 
distance to the old is equal to (8k/4)? = 97 = 4. 
More generally, if A/Ao is known at a point 
(he,d) for a transmitter height A; and for k = 4/3, 
the same value of A/Apo will be found at hy’, he’, d 
where Ee 
3 - 5 
h's,2 — ina() 5 
—2)3 
d=d (2) : 
4 
(168) 
(169) 
(170) 
