Table of Contents
Advertisement
3.6 Cable Compensation (Extension)
In order to connect the instrument and DUT, usually we can calibrate on the end
of the RF cables; but in some restricted occasions, users can either appeal to the
system calibration or just calibrate it by manual, thanks to the compensation function
that erases the influences by the cables on measurement. Of course the second
method brings about lower accuracy rate than the first method does.
Firstly, strictly follow the steps shown in Section 4.3 to test the exact electrical
length of the cable. If the cable's velocity coefficient is already known, electric length
can derive from calculating cable's mechanical length. But it will be less accurate than
actually measuring it.
When the cable cannot be disconnected from the antenna easily, users can again
turn to Section 4.3 to test the electric length. Choose those frequency bands whose
phase variation tendency is steady, meanwhile phase-frequency characteristics curve
should be rather straight. In this way, usually the tested electric length will extend to
antenna's feed point, which is a more effective way to do the calibration than
adjusting the antenna. This method also applies to the occasion where calibration is
executed on the end of the feeder in that by doing so, users can maintain the phase
plane extended to feed point.
Press FUNC to enter system setting interface. There is an item
Enter the testing result into "Cable Length".
"Cable attenuation" means antenna's single attenuation in "Cable frequency".
The best way to measure cable attenuation is using S21. But sometimes in reality,
users may be set back from performing the calibration on the other side, in other
word, fail to do the S21 measurement. There we need to enter the data from the
cable's factory. Of course we can also appeal to S11 to measure it in far-end open
circuit: if there are fluctuations in the curve, take the wave crest of less attenuation
near the final-expected frequency band. Pay attention that the reading number
should be divided by 2. When the attenuation is unsure, set it as 0.
Once "Cable data" is set, instrument will try to cancel the cable influence with it.
After the measurement is done, reset the parameters in time to prevent mistakes in
future use.
Cable parameter is also effective in S21 measurement.
3.7 Using the External Bridge
Access the "Advanced Settings" via combined keys SHIFT + 7 in the FUNC menu,
and make sure if the S11 BRIDGE is on EXT mode. Then the input port should go with
the left port of the instrument (Port 2), the output port should go with the right one
(Port 1). In this situation, attenuators in series are generally recommended.
Additionally, S11 calibration must be done before measurement.
Higher accuracy rate can be achieved through an external bridge with better
configuration than an internal bridge.
3.8 Necessary Preparation
- 21 -
Cable data".
"
Advertisement
Table of Contents
