S820E Microwave Site Masterâ„¢ User Guide : Vector Voltmeter : Relative Measurements
Relative Measurements
Often, absolute phase measurement of a DUT (cable in the following example) is not as important as the phase relationships among multiple DUTs. For the following example application, the Vector Voltmeter is used to make relative phase measurements.
The operations for relative measurements are described in the following steps.
1. Preset the S820E, then set up for this measurement by setting the frequency and the measurement type and format.
Measurement format may be LogMag/Phase, LinMag/Phase, SWR, or Impedance. LogMag/Phase measurement format is used in this example. You may change the measurement format at any time. If a reference value has already been recorded in a particular measurement format, and if you change the measurement format, then the reference value is automatically converted to the new selected measurement format.
2. Since many VVM measurements are made relative to a stored reference, vector error correction is not absolutely required. Absolute Reflection or Transmission measurements require calibration to remove residual errors, including port match errors. Refer to VVM Calibration for more details.
For A/B or B/A measurements, vector error correction of the instrument is not possible. In some cases where the measured results are unstable or not as expected, the overall measurement results may be improved simply by adding 3 dB or 6 dB attenuators on each measurement port (A and B). The process of storing the reference value will need to be repeated if attenuators are added after the initial reference value was stored.
3. Connect the first DUT (device under test).
4. If you want to use the measurement result of this first DUT as your reference (the golden DUT), then press the Save Reference submenu key.
5. As shown in Figure: Relative Reflection Measurement, the current measurement is saved and displayed as the Reference Value (at the top of the VVM display). The displayed values are now relative to the saved values, which are the difference between the current measurement and the saved reference. In other words, saving a reference will normalize the results to the current measurement.
The amplitude and phase windows now display Relative Value, and their text and data are displayed in green. If you clear the reference values, then the data are again displayed in black.
Relative Reflection Measurement
6. Additional DUTs may be connected consecutively (as required), and their relative results will be based on the stored reference.
7. To create a new reference, press the Clear Reference submenu key, then press the Save Reference submenu key while measuring the DUT for which you want to capture the new reference values.
If you are making many measurements, the display format can be set to Table. Refer to Table Display Format.
Clearing the reference while using the Table Display Format will immediately clear all of the relative measurement values that have been stored within the table.
Saving a new reference value while using the Table Display Format will immediately recalculate and display all of the relative measurement values with respect to the new saved reference.
You can change the current reference without pressing the Clear Reference submenu key. When the current measurement is desired as the new reference, press the Save Reference submenu key.
This completes the procedure for relative measurements.