Ceyear 4051 Series, User Manual

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4. Operating Instruction
4.2 Advanced operation guide
92
4.2.1.3 Distinguish measurements of two signals with constant amplitude
1) Basic Concepts
For frequency response of a simple-frequency signal, the Series Signal Analyzer has a trace of the shape of the
selected IF filter (usually referred as resolution bandwidth (RBW) filter). When the filter bandwidth is
changed, trace width shown by the analyzer will change accordingly. The resolution bandwidth is usually
defined as 3 dB bandwidth of the filter. Or sometimes, 6 dB bandwidth of the filter.
A basic characteristic of the Series Signal Analyzer is that it can separate each spectrum component from a
composite signal. While separation of such component depends upon the resolution bandwidth used. If the
resolution bandwidth is too large, it may be impossible to distinguish each spectrum component, thus
displaying only one signal.
To distinguish two signal of constant amplitude, the resolution bandwidth has to be less than or equal to signal
frequency interval. If the resolution bandwidth is equal to the frequency interval, a 3 dB dip will appear in the
spectral view between two signals. The smaller the resolution bandwidth is, the deeper the dip goes. Therefore,
distinction between signals will be clearer.
For Series Signal Analyzer in sweep mode, the sweep time is automatically set as 1/RBW
2
to ensure
measurement accuracy. With frequency span remaining unchanged, if the bandwidth is narrow, higher
frequency resolution should be obtained at the cost of higher sweep time. If the resolution reduces by 10 times,
the sweep time will increase by 100 times. In 4051, RBW can be set to as large as 20 MHz.
To optimize sweep time and maintain standard measurement of the analyzer, the sweep time (
【
Sweep
】
,
[Sweep Time]) and sweep type ( 【 Sweep 】 , [Sweep Setup] and [Sweep Type]) can be set as auto.
2) Measure two signals with frequency interval of 100 kHz
In this section, two signals of constant amplitude with frequency interval of 100 kHz are analyzed by reducing
their resolution bandwidth and video bandwidth. Attention should be paid to ensure that the resolution
bandwidth selected should be equal to signal frequency interval and that the video bandwidth should be
slightly smaller than the resolution bandwidth.
Step 1. connect two signal sources to the RF input port of the analyzer as shown in Fig. 4.7.
Fig. 4.7 Test instrument connection diagram of two input signals
Step 2. set frequency of one signal generator at 300 MHz and the other at 300.1 MHz and them set
output amplitude of both generators at -20 dBm.
Step 3. set the Series Signal Analyzer in spectrum analysis mode and reset:

Press 【 Mode 】 and [Spectrum];
 Press
【
Preset
】
.
Step 4. set parameters of the analyzer:
 Press
【
Frequency
】
, [Center Freq] and enter 300 MHz.