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Making Measurements
Example 9: Adjacent Channel Power Measurement
ATT N
=
PdB
opt
ChBW
(
)log
+
10dB
---------------------
NBW
where:
ATTN
is the optimum choice of attenuation.
opt
ATTN is the attenuator setting chosen within 10 dB increments.
PdB
is the transmitter power in units of dBm.
TX
DANL
is the displayed average noise level specification for the
Ref
analyzer, in dBm, with no input attenuation.
ML
is the mixer level for which third-order distortion is
Ref
specified in the spectrum analyzer.
TODdB
is the ratio of the signal power to the distortion
Ref
component power for the third-order distortion specification, in
dB, a positive number.
ChBW and ChSpacing are the channel bandwidth and channel
spacing parameters NBWRef is the noise bandwidth for the
resolution bandwidth in which DANL is specified; the NBW is
1.055 times the resolution bandwidth for RBW less than or equal
to 100 Hz.
Given this optimum attenuation, and a 10 dB step-size in the input
attenuator, choose the input attenuator in the range:
Adjacent Channel Power (ACP) Computations
The analog method calculates ratios for the upper and lower adjacent
channels of the power within these channels to the total transmitter
power. The total transmitter power is computed as follows:
PWRT
where:
x1 and x4 are positions of the trace data points at the left edge of
the lower adjacent channel and the right edge of the upper
adjacent channel, respectively.
116
1
(
)
–
3.84dB
–
-- - DAN L
TX
Ref
3
ChSpacing
(
)
–
20dB
log
2
–
---------------------------- -
ChBW
Ref
<
ATTN
ATT N
+
5.80dB
opt
>
ATTN
ATT N
–
4.20dB
opt
x4
∑
(
)log
P x ( )
=
10dB
x
10
x1
+
2M L
+
TODdB
Ref
Ref
SPAN
-------------- -
600
-------------------- -
+
RL
NBW
Chapter 2
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