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If the dBc method is selected, you can press [Measure], [OBW] and [dBc -3.00dB] and use the number keys,
UP/DOWN keys or knob to change the dBc value. The dBc range is -0.1dB to -100dB, with the minimum step of
0.01dB. The default setting is -3dB.
j) Change the occupied bandwidth span:
Press [Measure], [OBW] and [Span], and enter the occupied bandwidth span with number keys. Press
corresponding soft keys to enter the unit. The default setting is 3MHz.
k) Disable the occupied bandwidth measurement:
Press [Measure], [OBW] and [OBW Off
On], and disable the occupied bandwidth measurement. The interface will
change into the spectrum measurement interface.
3 Adjacent channel power ratio measurement
Taking the measurement of the adjacent channel power ratio of the FM signal for example, this section describes
how to use S3302 series spectrum analyzer to measure the adjacent channel power ratio.
1) Definition of adjacent channel power ratio
The adjacent channel power ratio (ACPR), also known as the adjacent channel leakage power ratio (ACLR) refers
to the ratio of the transmitted power of one channel to the radiation power of the adjacent channel. It is generally
expressed as the ratio of the power within the specified bandwidth under various offsets of the adjacent channel to
the total power of the channel. The adjacent channel power mainly depends on the extension of the modulated
sideband and noise of the transmitter.
The adjacent channel power ratio measurement can be applied, as a substitute of the traditional dual-audio IM
distortion measurement, in nonlinear system tests. The measurement result of the adjacent channel power ratio can
be expressed in two forms: power ratio and power density.
2) Measurement procedures
In the traditional measurement of the narrow-band signal, the distortion performance of the transmitter is evaluated
generally by means of dual-audio signal IM measurement. The broadband modulation signal includes both the
dense spectrum components and high peak signal (also known as the crest factor). IM products of spectrum
components of the signal are always around the spectrum. The IM measurement of the broadband FM signal is
complex, while ACPR is closely related to IM products arising from nonlinear distortion. Therefore, ACPR is a better
method to measure the nonlinear distortion of the broadband FM signal.
The ACPR of the broadband FM signal can be measured with the ACPR measurement function of S3302 series
spectrum analyzer according to the following procedures.