The Bolton Technical 4 way, Low-PIM splitter is an extremely low loss, high quality splitter designed for multiple indoor antenna runs. It splits the outgoing signal into four equal strength lines for continued cable runs, with a loss of up to -6 dB for each.PIM stands for Passive Intermodulation and is measured in dBs (decibels). PIM is defined as the unwanted signal or signals generated by the non-linear mixing of 2 or more frequencies. High PIM means poor cellular reception and limited bandwidth to the end user, which in turn means lost customers to the carrier. Low-PIM means strong signals with more bandwidth for more users - in other words, better signal and lower loss within your splitter, providing increased performance.A 4 way splitter is best used for high powered systems that want four separate antennas. The splitter breaks a single cable into four with only up to -6 dB of loss on one end, allowing you to bypass building material and increase the effectiveness of your cellular system.This allows one port for an indoor antenna to be multiplied into four with minimal loss. These are best used for powerful systems to send signal to four different areas of a large building. If you want four antennas on your system, this is an essential accessory.