Anritsu S331C - Manual (Page 74)

Antenna Calculations
The following is a list of various antenna calculations should you find it necessary to con-
vert from one to another:
Conversion of signal levels from mW to
mV in a 50-ohm system:
P
V
R
=
2
where: P = power in Watts
V = voltage level in Volts
R = resistance in Ohms
For power in milliwatts (10
-3
W), and voltage in microvolts (10
-6
V):
( ) ( ) VdB V P dBm m
= +107
Power density to field strength. An alternate measure of field strength to electric field is
power density:
Pd
E =
2
120
p
where: E = field strength in V/m
P = Power density in W/m
2
Power density at a point:
Pd
PtGt
r
=
4
2 p
In the far field, where electric and magnetic fields are related by the impedance of free
space:
P
d
= power density in W/m
2
P
t
= power transmitted in Watts
G
t
= gain of transmitting antenna
r = distance from the antenna in meters
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Chapter 5 Spectrum Analyzer Measurements