Campbell TGT1, Руководство оператора

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D-1
Appendix D. Detailed
Forward/Reflected Power Information
D.1 Impedance Matching
The reflected power to forward power ratio shows the degree of impedance
match between the transmitter and the cable/antenna assembly. The percent of
power reflected approximates the impedance match with the following
equation:
% power reflected = [((ref + 17.4)/(fwd + 17.4))
2
x 100] - 1
This equation is an approximation because some of the power reflected to the
transmitter can be reflected back to the antenna and then reflected back to the
transmitter. These multiple reflections can cause incorrect readings, especially
when the reflected power is large.
Impedance matching is also measured as reflection coefficient (
Γ
), Voltage
Standing Wave Ratio (VSWR), and Return Loss (RL). Table D.1-1 correlates
values between the different measurements.
Table D.1-1. Impedance Matching Correlation
% power ref
Γ
VSWR RL
1 0.1 1.2 20
2 0.14 1.3 17
5 0.22 1.6 13
10 0.32 1.9 10
20 0.44 2.6 7
50 0.71 5.8 3
80 0.89 17.9 1
D.2 Calculating Power-Out
The amount of power going out of the transmitter at the BNC connector is
approximated by the following equation:
Approx P
out
= (10 log[((fwd + 17.4) x 0.0100077)
2
x 1000/50]) + 20.8
This equation assumes the dBm is 50 ohms and the impedance match between
the trans-mitter and the cable/antenna assembly is good (% power reflected less
than 5). Table D.2-1 lists P
out
for various values of forward power.