Ceyear 4041 Series, User Manual

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Chapter IV Spectrum Analyzer Mode
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1) Definition of adjacent channel power ratio
The adjacent channel power ratio (ACPR), also known as the adjacent channel leakage ratio (ACLR), refers to the
ratio of the transmitted power of a channel to its radiated power at adjacent channels. It is typically represented by
the ratio of the power in the specified bandwidth at different frequency offsets of adjacent channels to the total
power of the channel. The size of adjacent channel power mainly depends on the extension of modulated sideband
and the noise of transmitter.
The measurement method for adjacent channel power ratio can replace the traditional measurement method for
dual audio intermodulation distortion and be applied to the nonlinear system test, and the measurements of
adjacent channel power ratio can be expressed as power ratio or power density.
2) Measurement procedure
In traditional measurement, for narrow-band signals, dual tone signal intermodulation measurement is commonly
used to evaluate the distortion performance of the transmitter. However, the wideband modulation signals not only
have very close spectrum components, but also have very high spike signals (referred to as crest factors), these
intermodulation products of the signal spectrum components tend to fall around the spectrum. Since the
intermodulation measurement of WBFM signal is quite complex and the adjacent channel power ratio (ACPR) is
closely related to the intermodulation products caused by the nonlinear distortion, the adjacent channel power
ratio (ACPR) is a better way to measure the nonlinear distortion of WBFM signals.
The procedure for measuring the adjacent channel power ratio of WBFM signal with the adjacent channel power
ratio measurement function of 4041 series spectrum analyzer is as follows:
a) Set the signal generator so as to output WBFM signal:
Set the frequency to 1 GHz, the power to -10 dBm, the frequency modulation frequency offset to 500 kHz, the
modulation rate to 10 kHz, and then connect the output of signal generator to the RF input of spectrum analyzer
with the cable, as shown in Fig 4-1, in order to generate a FM signal with the signal generator. Turn on the
modulation output switch and the RF switch.
b) Preset the spectrum analyzer to default state:
Press
【
Preset
】
.
c) Set the reference level of the spectrum analyzer:
Press
【
Ampt
】
, [Ref Level] and -10 [dBm];
Press
【
Ampt
】
and [Scale/Div] successively, and then set the scale to 10 dB/division.
d) Set the resolution bandwidth and video bandwidth:
Press
【
BW
】
and [Res BW Auto Man] successively, and then set the resolution bandwidth to 30 kHz;
Press
【
BW
】
and [Video BW Auto Man] successively, and then set the video bandwidth to 30 kHz or less.
e) Switch to adjacent channel power ratio measurement:
Press
【
Measure
】
, [ACPR] and [ACPR Off On] successively, and then switch to the adjacent channel power ratio