Ceyear 4051 Series, User Manual

Page: 133 / 751

4. Operating Instruction
4.2 Advanced operation guide
119
Fig. 4.33 shows the AM signal displayed on the screen of the analyzer. Press 【 Peak Search 】 to define
carrier signal frequency.
Caution
Amplitude different between upper and lower sideband indicates that there is residential frequency modulation
on the input signal. Residential frequency modulation will reduce modulation depth and measurement
accuracy.
Step 3. define parameters of modulated signals easily with carrier and sideband via following
operations:
 Press
【
Peak Search
】
, [Delta Marker] and [Next Peak] to get the difference between the carrier and the
sideband signal. The frequency difference of two signals can be read via the delta marker, which is the
modulation speed of the measured AM signal and used to determine modulation depth as shown in Fig.
4.34.
Fig. 4.34 Relation graph of modulation depth and amplitude difference
When the amplitude difference in dB is obtained, the following formula can be used to calculate modulation
depth:
Where:
Δ dB refers to the amplitude difference of the carrier and the sideband.
4.2.6.3 Measure amplitude modulation speed with demodulation waveform
Step 1. connect output of the signal generator to the input port of the analyzer:
 Set the signal generator with an AM signal with output carrier of 300 MHz, amplitude of -10 dBm,
modulation signal of 1 kHz and AM depth of 80%.
Step 2. reset the analyzer and set center frequency, frequency span and sweep time:
 Press
【
Preset
】
.
 Press 【 Frequency 】 , [Center Freq] and enter 300MHz.