Ceyear 4051 Series, User Manual

Page: 82 / 751

4. Operating Instruction
4.1 Function operation guide
68
The measuring sensitivity of Series Signal Analyzer is closely related to the attenuator, so the higher the
attenuator is, the greater the inherent noise inside the Series Signal Analyzer is; and the measuring sensitivity
of Series Signal Analyzer will decrease with the increase of noise floor in the trace display area. The
attenuator is usually set as 0 dB to obtain higher measuring sensitivity. The measuring sensitivity will
decrease by 10 dB and the corresponding average noise level displayed increases by 10 dB as the decrement
increases by every 10 dB. Therefore, the decrement of attenuator should be decreased usually to improve the
SNR of measuring signal. However, the greater decrement set can prevent the Series Signal Analyzer from
intermodulation or harmonic distortion, and, in such case, the RF amplification circuit at the back of mixer
can re-amplify the signal.
Accordingly, the attenuator can be set as distortion measurement or high sensitivity measurement to complete
the complicated measurement. If you have not understood the functions of attenuator thoroughly, it is
suggested that the attenuator should be set as auto coupling.
Prompt
Benefits of setting attenuator manually
When you are executing the distortion measurement, such as harmonic distortion or intermodulation
distortion, the greater decrement set is of great help and helps to determine whether the distortion is caused by
Series Signal Analyzer.
When you are executing the weak signal measurement, the attenuator is set as 0 dB, which is an effective
method for increasing the measuring sensitivity of Series Signal Analyzer.
Two types of attenuators including mechanical attenuator and Elec Attenuator are provided for the 4051
Series Signal/Spectrum Analyzer. Wherein the mechanical attenuator includes one mechanical attenuator with
step of 2 dB, maximum decrement of 6 dB and AC/DC switch function and one mechanical attenuator with
step of 6 dB and maximum decrement of 66 dB, which jointly form the attenuator component with minimum
step of 2 dB and maximum decrement of 72 dB. The connection relation is shown in Fig. 4.1.
Fig. 4.1 Connection Relation of Attenuators of 4051 Series Signal/Spectrum Analyzer
 Set mechanical attenuator manually
Generally, the mechanical attenuator is set automatically based on the reference level set with step of 2 dB.
The Series Signal Analyzer will automatically set the attenuator based on the following formula:
Decrement of attenuator = reference level + gain of PreAmplifier + external gain - reference level offset -
maximum mixer level + IF gain
Wherein: if the options of PreAmplifier are not set, its gain is 0 dB; IF gain is the variable gain amplifier at the
back end of the circuit of mixer, invisible for the user, which is set automatically by the Series Signal
Analyzer based on the reference level.
In addition, the attenuator values automatically set are greater than or equal to 6 dB. The decrement of
attenuator calculated based on the formula above is rounded up to an integer and parameters are set based on
the step of mechanical attenuator, automatically selecting the closest decrement. E.g., if the decrement of