Boonton PIM 31 User Manual - Manual (Page 77)

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11 What is PIM?
PIM distortion is caused by non-linear mixing of two or more frequencies in
passive devices like cables and connectors. Ideal passive devices are
considered linear. In reality any linear component has a non-linear factor that can
cause PIM distortion. For optimal operation of RF systems, PIM has to be kept at
a very low level that has virtually no influence on the network operation. PIM
signals are generally unwanted because they can interfere with signals in a
receive path.
11.1 What Causes PIM ?
Passive intermodulation can be caused by a variety of factors. PIM distortion is
often the result of flaws in component design and manufacturing processes. PIM
distortion may also be caused by wear and tear on components due to
mechanical constraints or environmental conditions.
11.1.1 Manufacturing & Design
• Use of ferromagnetic materials, such as nickel or steel, within the current
path. Especially at higher power levels, PIM can be generated due to
hysteresis effect of these materials and the non-linear voltage to current
ratio.
• Contaminations, like particles from machining operations or soldering
splatters that touch current carrying surfaces.
• Separation of current carrying contact zones through irregular contact
surfaces, corrosion and insufficient contact pressure.
• Dissimilar metals at contact areas.
• Insufficient thickness of plated metal causing RF heating through the skin
effect of RF.
• Bad solder joints.
11.1.2 Mechanical
• Poor mechanical alignment of components
• Too much or too little torque at connections
• Contaminated connectors