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by its self-contained calibration (where applicable).
Then, attach the mismatched calibration
(see Figure 2) load to the test
port of the hybrid tee. Note: A short circuit cannot
be used to calibrate a hybrid tee. Apply a signal to the input of the coaxial directional coupler. Ensure that the flange of the calibration load is securely attached to the test port of the tee. Loosen the setscrew and slide the mismatched load completely in towards the tee. This moves the tip of the load into the hybrid tee body and beyond the flange junction. While observing the oscilloscope, slowly withdraw the mismatched load and note the first maximum and minimum readings. Convert the readings to reflection coefficients (see Mismatch Conversion Table) and calculate the mean of the two. Then reconvert to return loss or VSWR. This represents the value of the mismatch at that frequency. Adjust the calibration controls of the associated equipment accordingly. Repeat the process to check that the mean value corresponds to the calibration of the load. |
Without further adjustment to the calibration controls,
determine the mean measured values for the other frequencies in
the band. The figures so obtained for reflection coefficient
should agree with the calibrations of the mismatch to within
an accuracy of ± 5% (typically ± 1 or 2%). Further improvement in accuracy can be obtained by averaging the calibration errors across the band. Provided that the mismatch calibration is correct, this test confirms that the detectors and sweep equipment are operating properly. The calibration of the test set is complete and the measurement may proceed. In the process of calibrating the sweep equipment, the directivity of the hybrid tee may be confirmed. This procedure is described in the following section on sliding loads. Caution: Always fully withdraw the sliding load into the load body and tighten the setscrew before removing the load body from the hybrid tee as shown in Figure 3. This prevents damaging the fragile tip of the load element. |