Specifications

74 Chapter 9
Measuring Digital Communications Signals
Making Adjacent Channel Power (ACP) Measurements
Measuring Digital Communications
Signals
Making Adjacent Channel Power (ACP)
Measurements
The adjacent channel power (ACP) measurement is also referred to as
the adjacent channel power ratio (ACPR) and adjacent channel leakage
ratio (ACLR). We use the term ACP to refer to this measurement.
ACP measures the total power (rms voltage) in the specified channel
and up to six pairs of offset frequencies. The measurement result
reports the ratios of the offset powers to the main channel power.
The following example shows how to make an ACP measurement on a
W-CDMA base station signal broadcasting at 1.96 GHz.
Step 1. Using an ESG, setup a W-CDMA signal transmitting at 1.96 GHz and
−10 dBm. Connect the RF OUTPUT to the spectrum analyzer RF
INPUT.
Step 2. Preset the analyzer, set the analyzer center frequency to 1.96 GHz.
Press
Preset, Factory Preset (if present).
Press
FREQUENCY Channel, Center Freq, 1.96, GHz.
Step 3. Set the analyzer radio mode to 3GPP W-CDMA as a base station device:
Press
Mode Setup, Radio Std, 3GPP W-CDMA.
Press
Mode Setup, Radio Std Setup, Device (BTS).
Step 4. Select the adjacent channel power one-button measurement from the
measure menu and then optimize the reference level and attenuation
settings suitable for the ACP measurement (see Figure 9-6):
Press
MEASURE, ACP.
Press
Meas Setup, Optimize Ref Level.
NOTE Optimize Ref Level protects against input signal overloads, but does not
necessarily set the input attenuation and reference level for optimum
measurement dynamic range.
To improve the measurement repeatability, increase the sweep time to
smooth out the trace (average detector must be selected). Measurement
repeatability can be traded off with sweep time.
To increase dynamic range,
Noise Correction can be used to factor out
the added power of the noise floor effects. Noise correction is very useful
when measuring signals near the noise floor of the analyzer.