China Electronics Technology Instruments AV3672 Series, User Manual

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Appendix
Appendix 3 Frequency Offset Measurement
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2) The independent intermediate frequency bandwidth and independent sweep time are valid for the main setting
and non-coupling receiver and invalid for the source.
3) The independent power is valid for the main setting and non-coupling source mode and invalid for the receiver.
3.3 Calibration of Frequency Offset Measurement
In the traditional calibration process, errors are corrected through the measurement reference channel. The stimulus
frequency is different from the response frequency in frequency offset measurement. Therefore, the traditional
standard calibration mode cannot be used for error correction, such as the full double-port SOLT mode. The source
and receiver power calibration mode should be applied for error correction in the frequency offset measurement.
Click [Cal] > [Calibration...] > [Power calibration] on the front panel and open the [Power calibration] option.
For details, refer to “7 Calibration”.
1) Source power calibration
➢
On the premise of no consideration to the receiver accuracy, set the accurate power corresponding to the
stimulus frequency.
➢
No channel copying function.
2) Receiver calibration
➢
Set a calibrated source.
➢
No channel copying function.
3) Mismatch error
If the connector of different impedance is connected between measurement points, mismatch error will occur. The
mismatch error can be eliminated by means of full double-port calibration in S-parameter measurement. This
problem cannot be solved easily in frequency offset measurement. The simplest way is to connect a high-quality
attenuator between the input end and the mixer output port. The ports can be matched effectively by adding one
attenuator between ports, so as to increase the attenuation value to be more than twice. The larger the attenuation
value is, the better the improvement effect is good, but the smaller the dynamic range of measurement is.
4) LO accuracy and stability
If the LO signal is not accurate or stable in the frequency offset measurement mode, the output signal will be
beyond the edge or band-pass of the intermediate frequency filter. At the same time, the LO power also plays an
important role in mixer measurement. Therefore, the LO power accuracy and stability must be ensured.
3.4 Typical Application of Frequency Offset Measurement
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Frequency transformation loss (gain) measurement
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399
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Frequency transformation compression measurement
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400
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Isolation measurement ····························································································· 400
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Harmonic distortion measurement ················································································ 402
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Return loss and standing wave ratio measurement ······························································ 402
3.4.1 Frequency Transformation Loss (Gain) Measurement
The frequency transformation loss is defined as the power ratio of the output frequency and input frequency at the
given LO power. The LO power has the influence on the frequency transformation loss. The frequency
transformation loss reflects the energy conversation efficiency of the input signal of the mixer from the current
frequency into the output frequency. If the frequency transformation loss is not flat within the measurement
frequency range, part of valuable information of the output signal will be lost.
Transmission measurement should be applied to measure the frequency transformation loss. The input signal power
will be measured by entering the specific stimulus and LO signal power. If the output frequency is different from
the input frequency, the frequency offset measurement must be applied.