ETS-Lindgren 3147 Log Periodic Dipole Array Antenna - Manual (Page 35)

8.0 Power Requirements
The Model 3147 Log Periodic Dipole Antenna may also be used as a transmitting
antenna. The power input requirements for a desired electric field strength level
are provided in the Power Requirements table on page 36. The power is
computed 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
In the Power Requirements table on page 36, R is 3 meters. It is measured from
the center of the antenna as per ANSI C63.5. The power limitation is 80 Watts
maximum continuous power for frequencies below 1 GHz and 40 Watts
maximum continuous power above 1 GHz. An asterisk indicates where the power
required to generate a certain field level exceeded the maximum continuous
power rating. As an example, to generate a 20 V/m electric field at 1 GHz, 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:
Pt =
|E| 2 R 2
=
(20 2 )(3 2 )
= 24
30 g 30(5)
Power Requirements | 35