Ceyear 4051 Series, User Manual

Page: 131 / 751

4. Operating Instruction
4.2 Advanced operation guide
117
Step 5. move the marker to 500 MHz:

Press 【 Marker 】 and turn the knob on the front panel to set noise marker reading as 500 MHz.
The noise marker value is derived by multiplying the number of sweep trace points with 5% and the marker
position is the center of such trace points. The noise marker will not be at the signal peak since such position
has no enough trace points for calculation. Therefore, when the resolution bandwidth is narrow, the noise level
will average trace points below the signal peak. As shown in Fig. 4.32.
Fig. 4.32 Measure noise with the noise marker function
Step 6. set the analyzer as zero frequency span with the marker as the center:
 Press 【 Marker → 】 and [Marker → Center Freq].

Press Span/X Axis] and [Zero Span].
 Press
【
Marker
】
.
The amplitude reading of the noise level is correct at the moment since all points are averaged under the same
frequency without being affected by the shape of the resolution bandwidth filter. The noise marker is derived
by averaging frequency points of interest. When measuring the power of discrete frequency points, the
analyzer should be tuned to the frequency points of interest and then the measurement should be made under
zero frequency span.
4.2.6 AM signal demodulation
4.2.6.1 Definition of modulation
Modulation refers to the process of transforming low frequency or base bad signals (sound, music and data) to
high frequency signals. During modulation, some characteristics of carrier signals (usually frequency or
amplitude) will change in proportion to transient change of base band signal amplitude. When demodulating
AM signals, the analyzer can serve as a fixed-tuned receiver (time domain), which means to use zero
frequency span mode to restore amplitude-modulated carrier signals.