Ceyear 4041 Series, User Manual

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Chapter IV Spectrum Analyzer Mode
27
signal to obtain the occupied bandwidth of the signal. The percentage of power mentioned above may be set by
the user.
b) dBc down method:
This calculation method defines the occupied bandwidth as the distance between the two frequency points when
the signal power on both sides of the frequency point where the peak power of the signal is located is reduced by
dBc. The power down dBc of the signal is to be set by the user.
2) Measurement procedure
The procedure for measuring the occupied bandwidth with the 4041 series spectrum analyzer is as follows:
a) Set the signal generator so as to output FM 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 center frequency:
Press
【
Freq
】
and [Center Freq] successively, and then set the center frequency of spectrum analyzer to the
frequency of the measured signal (i.e., 1 GHz) with the numeric key.
d) Set the resolution bandwidth:
Press
【
BW
】
and [Res BW Auto Man] successively, and then set the resolution bandwidth to an appropriate
value.
e) Set the video bandwidth:
Press
【
BW
】
and [Video BW Auto Man] successively, and then set the video bandwidth to an appropriate value.
To improve the accuracy of measurement, it is recommended that the ratio of RBW to VBW be greater than 10.
The ratio of RBW to VBW can be changed by pressing [RBW/VBW].
f) Switch the spectrum analyzer to the occupied bandwidth measurement mode:
Press
【
Measure
】
, [OBW] and [OBW Off On] successively.
After the occupied bandwidth measurement function is enabled, the spectrum analyzer switches to the occupied
bandwidth measurement, with the results displayed at the bottom of the screen. The schematic diagram of
occupied bandwidth measurement is as shown in Fig 4-3. The two vertical white lines on the screen visually
indicate the frequency range of occupied bandwidth. When the occupied bandwidth measurement function is
enabled, the detection mode will be switched to the RMS detection mode automatically if the spectrum analyzer is
in automatic detection mode. The user can change the measurement method, occupied bandwidth span and other
parameters through the corresponding menu and thus to obtain more accurate measurements.