When making Distance‑to‑PIM measurements, the ability to individually resolve two PIM sources that are physically close together is determined by the swept bandwidth of the IM (intermodulation product) product being measured. The more IM product frequency bandwidth available, the closer together two PIM sources can be resolved. Table: Typical Calculated Resolution of Sample Frequency Bands shows the calculated resolution for several of the MW82119B frequency bands, assuming a propagation velocity factor of 0.88. As can be seen in the table, some frequency bands have inherently better resolution than others.
Typical Calculated Resolution of Sample Frequency Bands1
The Enhanced Resolution feature typically improves the standard resolution by a factor of two during Distance‑to‑PIM measurements. This feature is enabled by default (refer to Figure: DTP Setup Menu). In Enhanced Resolution mode, the location of PIM sources on the line is estimated, and up to 4 impulse bars are displayed. The impulse bars mark the predicted location of the measured PIM sources. The vertical impulse bars are easy to read, and they clearly identify the location of multiple PIM sources (when they exist). See Figure: Example of Impulse Bars with Enhanced Resolution.
An error checking function is employed to compare the magnitude of the enhanced resolution prediction to the magnitude of the standard resolution prediction. If correlation between the two estimates is not good, then the impulse bars are not displayed.
Occasionally, false PIM locations will be predicted by the enhanced resolution algorithm. False predictions are more likely to occur when measuring an unstable PIM source (magnitude changing versus time), when measuring very low magnitude PIM signals, or when testing in a noisy RF environment. Even with the occasional false prediction, this technology can help operators find and eliminate PIM sources more quickly in the field.
