Chapter 2 113
Making Measurements
Example 9: Adjacent Channel Power Measurement
ACP Analog Method Definition
When using the analog method and the ACP auto measurement
function for making adjacent channel power measurements, the
spectrum analyzer center frequency should be set to the transmitter
intended center frequency. The reference level should be set to optimize
the displayed range to minimize the number of data points above the
top or below the bottom of the range of the chosen display scale. The
display scale should be set to LOG 10 dB/division. The input attenuator
should be set to optimize the tradeoff between analyzer-induced
third-order intermodulation distortions and noise.
When
ACP AUTO MEASURE is used with the analog method selected and
the number of alternate channel pairs is set to zero, the display reflects
the following:
• ACP ratio results in the lower channel (LOW) and upper channel
(UP), located in the active function area,
• channel spacing (CSP) and channel bandwidth (CBW) parameters,
located in the active function area, and
• total power transmitted (PWR Tx) and maximum adjacent channel
power (MAX ACP), located in the display title area.
Figure 2-53 illustrates how the channelbandwidth and channelspacing
parameters are defined. For more detailed information regarding how
an ACP measurement is determined, refer to "Adjacent Channel Power
(ACP) Computations" below.
The adjacent channel power measurement, as performed by the
spectrum analyzer using the analog method from the
ACP AUTO
MEASURE softkey, responds to signals in an rms fashion. This means
that the total power transmitted and adjacent channel power ratios are
accurately reported, whether or not the transmitted signal contains
tones, noise, or both. If the instrument state violates any of the
following constraints, the response of
ACP COMPUTE to signals is no
longer rms, and errors of up to −2.51 dB can occur for noise-like signals:
• Video bandwidth is at least 10 times the resolution bandwidth.
• Detector mode is SAMPLE.
• Resolution bandwidth is less than or equal to 100 kHz.
• Video averaging is OFF.
• Neither MAX HOLD nor MIN HOLD trace mode is selected.
When
ACP AUTO MEASURE is pressed and the measurement setup is
suitable for rms detection, the following adjacent channel power
message is briefly displayed in the active function area immediately
before the measurement is made.
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