Calibration for CAT, NA, and VVM Modes 67
o Higher than 0 dB indicates that you should recalibrate.
Verifying Phase Accuracy
Connect a LOAD standard at the calibration reference plane (where calibration
standards were connected).
In NA Mode, select a S11 Reflection with Polar or Smith Chart format.
Because all LOAD standards have delay, you should see a small amount of
phase rotation as a function of frequency.
In general, the measurement result should agree with the characteristics of the
calibration standard.
Test the Jumper Cable
With the LOAD standard still connected, move the jumper cable while observing
the trace.
If the measurement trace is relatively stable, the jumper cable is of good
quality.
If you observe significant movement in the peaks of the measurement trace
when moving the cable (>5 dB), the jumper cable may need to be replaced.
Using QuickCal to Calibrate at the End of a Long Cable
The QuickCal process requires that there be sufficient resolution (data points) to
unwrap the cable reflection phase correctly. This requirement is met by having a
step frequency (frequency span between data points) with a wavelength = (4*
length of cable(m)) / (velocity factor).
For a 5 meter cable with a velocity factor of 0.7:
wavelength = 4* 5m / 0.7
wavelength = 28.57
step freq = speed of light/wavelength.
step freq = 3e8 / 28.5
step freq = 10.5 MHz
Resolution = frequency span / step freq
For a 2 MHz to 6 GHz sweep:
Resolution = 5.998e9 / 10.5e6
Resolution = 571 points or greater.
On the FieldFox, select 601 points before calibrating.
In addition, for VERY long cables (100 ft) there may be too much loss to obtain
distinct measurements of the open, short and load.
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