Hi Walter
The formula is derived from the general one that is: E =
SQR(30*P*G)/D. Being the gain G of an half-wave dipole equal to 1.64,
30*1.64 = 49.2, rounded to integer and written out of the square root it
becomes 7. E is the field strength in V/mt, provided that P is in Watts and
D in meter; in fact the field strength is independent from frequency.
73 Cesare
Cesare Tagliabue I 5 TGC
e-mail: [email protected]
url: http://www.dadacasa.com/i5tgc
-----Messaggio originale-----
Da: Walter Blanchard <[email protected]>
A: [email protected] <[email protected]>
Data: mercoledì 7 giugno 2000 11.58
Oggetto: LF: Formula
I found the following in an article recently.
Quote:
"The intensity E (known as the field strength) of a transmission
at a distance D from a source transmitting P watts of RF power via
a half-wave dipole in a free, unobstructed space, can be estimated
using the formula:
E=(7*sqrt (P))/D.
Thus, for a 2 watt transmitter, the theoretical field strength in free
space at one metre distance is approximately 10 V/m and at 100 metres
distance 0.1 V/m"
This formula is new to me and I can't find it in any
textbooks I have. Since it ignores frequency shouldn't
it be power flux per unit area and not field strength?
Can anyone tell me where it comes from?
Walter G3JKV.
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