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Eliminate signal degradation in wireless network
By Ray Butler Vice President of Engineering Base Station Antenna Systems Andrew, a CommScope Company

SIGNAL

For wireless operators, usingpassive intermodulation distortion (PIM) equipment correctly requires greater care than standard voltage standing wave ratio (VSWR) site sweeps or distance-to-fault transmission line testing. Wirelessoperators have invested a lot of money into 3G networks and will continue to do so for the next generation of technologies, whether it’s HSPA+, LTE, or others. These investments are often overlaid on theexisting network, utilising existing tower equipment such as feeder coaxial cable lines and base station antennas. Operators are increasingly taking steps to avoid potential signal degradation thatcan result from overlays, especially when adding new frequency bands. One such concern is PIM distortion, and it’s enough of an issue that many operators are deploying PIM testing equipment to thefield. However, using PIM equipment correctly requires greater care than standard voltage standing wave ratio (VSWR) site sweeps or distance-to-fault transmission line testing. Two or more signals need tobe present for PIM to be created. Figure 1 shows examples of where it can be produced. PIM usually results from transmit signals mixing in the presence of an imperfect (or imperfectly installed) pieceof hardware, causing interference signals in the receive band. PIM is a major problem when the base receiver is at the same frequency as the PIM distortion, and the PIM is of sufficient level todegrade the desired signal. The probability of PIM distortion being an issue is higher with nextgeneration network broadband

Figure 1: Intermodulation – Where can it be produced? (diodes representnon-linear IM generator). This diagram provides an overview of the sources that generate or contribute PIM into your system.

signals such as LTE and when new frequency bands have been added....