Filtering

Harmonics, linearity, and spurious signals also introduce errors that are not removed by frequency response calibration. These errors are smaller with a narrowband detection scheme, but they may still interfere with your measurements. You should filter the IF signal to reduce these errors as much as possible.

Correct filtering between the mixer’s IF port and the receiver’s input port can eliminate unwanted mixing and leakage signals from entering the analyzer’s receiver. Figure 6-90 shows a plot of mixer conversion loss when proper IF filtering was neglected.

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Example of Conversion Loss versus Output Frequency Without Correct

IF Signal Path Filtering

Figure 6-91 shows the same mixer’s conversion loss with the addition of a low pass filter at the mixer’s IF port.

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Figure 6-91.

Example of Conversion Loss versus Output Frequency With Correct IF

Signal P&&I Filtering and Attenuation at all Mixer Ports

Filtering is required in both fixed and broadband measurements, but you can implement it more easily in the fixed situation. Therefore, when conllguring broad-band (swept) measurements, you may need to trade some measurement bandwidth for the ability to more selectively Alter signals entering the analyzer’s receiver.

6.160 ApplicationandOperationConcepts

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HP 8753E manual Filtering, J j j i