PASSIVE INTERMODULATION (PIM) Testing （无源互调(PIM)测试）.pdf

PASSIVE INTERMODULATION (PIM) Testing Guidelines ADVANTAGE PASSIVE INTERMODULATION (PIM) Passive Intermodulation (PIM) occurs when two or more high power RF signals encounter non-linear electrical junctions or materials in an RF path. These non-linear junctions behave like a mixer causing new signals to be generated at mathematical combinations of the original RF inputs. In the figure to the right, f1 and f2 represent two Tx frequencies present at a typical cell site and ± m•f1 ± n•f2 are RX Band TX Band the PIM signals generated by those Tx frequencies. When these PIM signals fall in the Rx band of the Example: f = 869 MHz, f = 894 MHz cell site the noise floor rises causing increased 1 2 dropped calls, reduced data transmission rates and IM3 = 2x 869 MHz - 1x 894 MHz = 844 MHz decreased system capacity. The impact of PIM on IM3 = 2x 894 MHz - 1x 869 MHz = 919 MHz the network performance can be severe, especially IM5 = 3x 869 MHz - 2x 894 MHz = 819 MHz for wideband systems such as CDMA, UMTS or LTE. IM5 = 3x 894 MHz - 2x 869 MHz = 944 MHz PIM SOURCES AT A CELL SITE The primary sources of non-linear junctions at a - Solid inner conductors distorted in the cell site are inconsistent metal to metal contacts