Chapter 2 117
Making Measurements
Example 9: Adjacent Channel Power Measurement
P(x) is the power ratio of the indicated trace data at point x to the
reference level. For example, if the trace data is −60 dB, P(x) is
0.000001.
SPAN/600 is the spacing of trace data points.
NBW is the effective noise bandwidth of the resolution bandwidth
used for the measurement. It depends on the shape of the
resolution bandwidth filter, the scale, and the detector mode. For
the ACP function, for most resolution bandwidths, the noise
bandwidth is approximately:
1.128 × 3 dB BW for RBW ≥ 300 Hz
1.055 × 3 dB BW for RBW ≤ 100 Hz
RL is the reference level in dB units.
The power in the lower adjacent channel is given by the same
expression, except that the upper summation limit is x2, the right edge
of the lower channel, instead of x4. Likewise, the power in the upper
channel includes summation limits from x3, the left edge of the upper
channel, to x4.
The ACP leakage ratio displayed as LOW (lower channel) is given in
decibels as the dB difference between the total power transmitted
(PWR Tx) and the power in the lower channel. UP is computed
similarly for the upper channel.
The edges of the adjacent channels, x1 through x4, are given by:
where:
Fc is the center frequency.
ChSp and ChBW are channel spacing and channel bandwidth.
RBW is the resolution bandwidth.
1/2 × 1/600 × SPAN is one-half of the spacing of trace data.
0.307 × RBW is a term that changes the effective passband shape
for the power measurement to a shape with a response that is −6
dB at the channel edges compared to the channel center.
x1 F
c
ChSp–
1
2
---
ChBW
– 0.307RBW
1
2
---
1
600
---------
SPAN
++=
x2 F
c
ChSp–
1
2
---
ChBW
0.307RBW–
1
2
---
1
600
---------
SPAN
–+=
x3 F
c
ChSp
1
2
---
ChBW
– 0.307RBW
1
2
---
1
600
---------
SPAN
+++=
x4 F
c
ChSp
1
2
---
ChBW
0.307RBW–
1
2
---
1
600
---------
SPAN
–++=
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