116 Chapter2
Making Measurements
Example 9: Adjacent Channel Power Measurement
where:
ATTN
opt
is the optimum choice of attenuation.
ATTN is the attenuator setting chosen within 10 dB increments.
PdB
TX
is the transmitter power in units of dBm.
DANL
Ref
is the displayed average noise level specification for the
analyzer, in dBm, with no input attenuation.
ML
Ref
is the mixer level for which third-order distortion is
specified in the spectrum analyzer.
TODdB
Ref
is the ratio of the signal power to the distortion
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:
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.
ATTN
opt
PdB
TX
3.84dB()–
1
3
---
DANL
Ref
2ML
Ref
TODdB
Ref
10dB()log
ChBW
NBW
Ref
---------------------
20dB()2
ChSpacing
ChBW
-----------------------------–log–
++
+
–=
ATTN ATTN
opt
5.80dB+<
ATTN ATTN
opt
4.20dB–>
PWRT
x
10dB()log
10
Px()
SPAN
600
---------------
NBW
---------------------
x1
x4
∑
RL+=
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