9. Tips for Getting the Best from the RTF System
9.1
RTF System Practices
There are a number of practices that will allow the best to be gained from the RTF system:
9.1.1 Cable & Connector Care
• Good quality connectors and test cables are essential for making accurate PIM vs Distance and Return Loss vs
Distance measurements.
• Take good care of the RF connectors on the RTF module and associated cables. Do avoid damaging the connectors
in transit.
• Care should be taken when mating the RTF module to the 7-16 Output Port connector on the iQA/iPA, or when mating
a cable to the 7-16 Test Port connector on the RTF module. Ensure the mating surfaces line-up correctly, and the
coupling nut does not cross thread. Tighten the locking nut by hand initially, and then only do a final torque using a
spanner. DO NOT allow the body of the RTF module to rotate. DO NOT over-torque, as this can cause permanent
damage to the 7-16 connector.
• Ensure that the 7-16 connectors on the iQA/iPA and RTF module are cleaned regularly, as lack of cleanliness is one of
the major causes of PIM problems. A cleaning kit is supplied within the iQA/iPA accessories kit for this purpose. Clean
connector mating surfaces using a cotton bud and an isopropyl wipe to remove dirt, dust & small metal filings.
• Keep protective caps installed on all RF connectors whenever they are not in use.
9.1.2 Making PIM vs Distance Measurements
•
The accuracy of PIM vs Distance measurements can be adversely affected by large return loss faults in the device
under test. Therefore it is strongly recommended that all large return loss faults be repaired prior to performing any
PIM vs Distance measurements.
• It is very important to ensure that the Max Distance setting is greater than or equal to the total length of the device
under test. The correct operation of the instrument cannot be guaranteed if this condition is not satisfied.
•
Be aware that some RF devices like filters, combiners and TMAs can have very long electrical lengths. Therefore
the Max Distance setting should be chosen to reflect the “apparent” length of the system, and not simply its physical
length. The apparent length can be determined by performing a Return Loss vs Distance measurement with an open
circuit termination at the far end of the device under test, and noting the location of the last peak on the trace. The
location of the last peak should be used as the Max Distance setting.
9.1.3 Making Return Loss vs Distance Measurements
•
The accuracy of Return Loss vs Distance measurements can be adversely affected by the presence of interfering
signals in the transmit band of the instrument. This situation frequently arises when performing Return Loss vs
Distance measurements on a system with an antenna installed, in which external interferers from other cell sites enter
the system through the antenna and cause errors in the measured return loss.
•
The presence of external interferers often shows up as a high noise floor on the Return Loss vs Distance trace. As
a rule of thumb, if the noise floor of a Return Loss vs Distance trace is less than 20 dB below the largest peak on the
trace, there is a good chance that external interferers are to blame.
9.2
Recommended Procedure for PIM Troubleshooting
9.2.1 Static and Dynamic PIM Faults
PIM faults in RF infrastructure generally fall into one of two categories: static or dynamic. The term “static” is used
to describe PIM faults that are relatively stable over time, and do not vary greatly when the system is perturbed by
mechanical stresses or vibrations. It is primarily this type of fault that the RTF system has been designed to detect.
By contrast, “dynamic” PIM faults are usually highly sensitive to mechanical disturbances, and can produce PIM levels
that vary widely from measurement to measurement. The RTF system cannot be relied upon to detect this type of fault.
In most cases the only way to detect dynamic faults is to perform a fixed-frequency PIM test on the RF infrastructure while
applying a percussive stimulus to each component and interconnect in turn.
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