ESCO Technologies ETS-Lindgren 3147, User Manual, Page: 39 / 49

Power Requirements | 39
8.0 Power Requirements
The Model 3147 Log Periodic Dipole Antenna may also be used as a transmitting
antenna. Please note the maximum power specification in the specification table
on page 13. The power needed to generate a given field strength in free space
can be estimated according to the transmission equation:
Power transmitted =
(field strength)
2
(distance in meters)
2
(30 x Numeric Gain)
Pt =
|E|
2
R
2
30 g
where E is the field strength (in V/m), R is the distance from the transmit
antenna. g is the antenna gain (in linear unit). The power limitation is 80 Watts
maximum continuous power for frequencies below 1 GHz and 40 Watts
maximum continuous power above 1 GHz.. As an example, to generate a 20 V/m
electric field at a given frequency, the measured antenna factor is 23.2 dB(m
-1
).
The gain in dB is computed using:
G(dB) = 20 log
10
(F
MHz
) – 29.79 – AF
G(dB) = 20 log
10
(1000) – 29.79 – 23.2 = 7.0
Converting this value to obtain numeric gain:
g = 10 0.7 = 5.0
Applying the formula for the power transmitted, at 3 m distance from the antenna
boresight,
𝑃
20 3
30 5
24 𝑊