Boonton PIM 21 User Manual - Manual (Page 8)

8 | PIM 21 User’s Manual
Purpose, Function and Features
Purpose, Function
and Features
Purpose
The PIM 21 is a portable test instrument for the detection of non-linear components and as-
semblies in radio base station installations.
Non-linear Radio Frequency (RF) assemblies cause Intermodulation Distortion (IM) and the
purpose of the Test Set is to specifically test for this distortion in passive components.
Components such as coax feeder assemblies, filters and antennas all fall into this passive
category, the common term to describe this distortion is Passive Intermodulation Distortion or
PIM.
This tester is designed to aid communications technicians in the field locate components and
assemblies which are creating PIM and degrading the performance of the installation.
The PIM 21 is not intended to be a laboratory instrument or replace such instruments. It has
been specifically designed for field portability and fault location.
Effects Of PIM
A non-linear transfer function is deliberately created in some devices such as mixers. When
two RF frequencies are applied to a mixer other frequencies or products are created. It is the
creation of these additional products which can cause problems in radio base station installa-
tions. For example, if the products of two transmitters fall on a receive frequency used at that
installation blocking may occur.
Measurement Theory
All passive RF components have some degree of non-linearity and the function of the PIM 21 is
to evaluate the amount.
Measurement of Passive Intermodulation distortion is typically performed with two excitation
frequencies (RF carriers) and a receiver tuned to the 3rd order IM product.
The frequency of the 3rd order product(s) can be calculated by the following:
IM3 = (2 x F1) – F2 or (2 x F2) – F1
Where IM3 = 3rd order product
F1 = First carrier frequency
F2 = Second carrier frequency
Results can be reported as absolute power measurement (-dBm) from the 3rd order receiver or
as a difference between the excitation carrier power and the receiver measured power (-dBc).
For all test cases the excitation carrier powers must be noted as this will affect the measured
PIM result.