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Bird AT-400 Antenna Tester
18
Measurement Units
Rho (Reflection Coefficient), VSWR (Voltage Standing Wave
Ratio), Match Efficiency (%), and Return Loss (dB), are
different units of measurement that can be used to present
the same information. (Similarly, Celsius and Fahrenheit
are different units of measurement used to express the same
temperature). These units can be used to express the degree
of match between an antenna system and a transceiver.
Rho is the ratio of reflected wave voltage to forward wave
voltage. A perfect antenna would not have any reflected
waves, hence would have a 0.00 reflection coefficient.
VSWR refers to the ratio of maximum and minimum
voltages that are set up on a transmission line resulting
from the combination of a forward wave and reflected wave.
If the antenna system is perfectly matched, the VSWR would
be 1:1 and shown as 1.00.
Match Efficiency (%) indicates how much of the
transmitted power is being used and how much is wasted. If
the antenna system is perfectly matched, the Match
Efficiency would be 100%.
Return Loss (dB) is a comparison of the reflected signal to
the forward signal in decibels. If the antenna system is
perfectly matched, the Return Loss would be negative
infinity dB.
Figure 5
Single
Frequency
VSWR
1.2
1.5
1
.
3
5
260.00 MHz
Freq
MHz
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