A procedure for the wear prediction of collector strip and contact wire in pantograph–catenary system

In multifrequency communications environments, such as land mobile radio sites, satellite earth stations, ships and surveillance aircraft, passive intermodulation products (PIMP) generated by nonlinear materials and metallic contacts can cause serious radio interference This problem is well known and a wide range of coaxial cables, connectors and materials have been investigated The paper gives an overview of passive intermodulation interference in communication systems It describes briefly the theory of intermodulation, types of passive nonlinearities, mechanisms responsible for the generation of PIMP, guidelines for minimising PIMP generation and techniques for locating PIMP sources Previous investigations of PIMP are summarised and the design of PIMP measurement systems is discussed An example of PIMP measurement is also included

Passive intermodulation interference in communication systems

A new model is presented for the calculation of passive intermodulation (PIM) in waveguide connections. The model considers the roughness of interconnecting waveguide surfaces and the presence of an insulator layer (oxide and contaminants) on these metal surfaces. This results in the generation of a contact resistance, which can excite the PIM level. In particular, the case in which metal-insulator-metal regions are the PIM source is especially investigated. The intermodulation level response is calculated for different waveguide junction parameters like applied mechanical load, surface finish, or metal properties showing qualitative agreement with the measured data published by previous authors.

Passive-intermodulation analysis between rough rectangular waveguide flanges

Effect of arc discharge on wear rate of Cu-impregnated carbon strip in unlubricated sliding against Cu trolley under electric current

Coaxial connectors are frequently the dominant contributors to passive intermodulation (PIM) distortion in high-frequency networks. This paper reports on a circuit model enabling estimation of PIM distortion by coaxial connectors in the design of high-frequency networks. A method of modeling the effect of multiple point sources of PIM is applied to coaxial connectors, allowing the prediction of the PIM of networks with several connectors. Typical ranges of PIM produced by common connectors in a two-tone test are reported. The stability and repeatability of PIM produced by a single connector is examined. Nonlinear current-voltage curves for coaxial connectors are given that predict the PIM distortion output by coaxial connectors over a broad range of input powers. An experimental verification is given showing that PIM of a system can be predicted if the characteristics of the individual components are known.

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Prediction of Passive Intermodulation From Coaxial Connectors in Microwave Networks

Generation of intermodulation products arising from nonlinearities at metal-to-metal contacts for microwave frequencies has been investigated. Detailed studies concentrated on the intermodulation products generated at contacting faces between both similar and dissimilar metals, and included contact materials of copper, beryllium-copper, brass, oxygen-free nickel, mild steel, stainless steel, aluminium, and twelve home-made steels with various compositions. The surface properties of the materials were found to be of prime importance. Measurements were carried out at frequencies around 1.5 GHz. The variations of the 3rd- and 5th-order intermodulation product levels with power levels of the fundamental signals and with the axial force applied to the contact were studied.

Nonlinearities in Metal Contacts at Microwave Frequencies

Wear in simulated railway overhead current collection systems

Intermodulation interference arising from nonlinearities in braided coaxial cables at microwave frequencies is discussed. Detailed investigations have been carried out using a large number of commercially available and specially constructed cables to isolate and assess the relative contributions of different parameters of coaxial cables responsible for the generation of intermodulation products (IP's) at L-, S-, and C-band frequencies centered on 1.5, 3, and 5 GHz. Ambient temperature in the case of polythene dielectric cables and oxides on copper-wire braids affect considerably the IP's generated in a coaxial cable.

Coaxial Cables as Sources of Intermodulation Interference at Microwave Frequencies

The electromagnetic interference (EMI) from various forms of electrical discharges was investigated, and the measured levels were compared with civilian and military statutory limits of interference. The more stable arc forms, such as moderate-current (50-250A) arcs in argon flow, gave low levels of EMI conforming with all statutory limits throughout the frequency spectrum (0.1-1000 MHz). The interference from high-frequency/high-voltage spark discharges, used for arc initiation, was found to exceed statutory limits if used on a continuous basis.

Electromagnetic Interference from Electric Arcs in the Frequency Range 0.1-1000 MHz

The stability of free-burning copper arcs in air has been investigated using a variety of electrode configurations. The longest lifetimes are obtained using a hollow-cratered cathode which yields lifetimes of more than 10s in the current range 50–250 A. These times are more than one order of magnitude higher than the lifetimes obtained with a pointed-rod cathode. Distortion of the electrode surface, due to prolonged arcing, reduces the arc lifetime.

Frank A. Benson

Papers

Nonlinearities in Metal Contacts at Microwave Frequencies

Wear in simulated railway overhead current collection systems

Coaxial Cables as Sources of Intermodulation Interference at Microwave Frequencies

Electromagnetic Interference from Electric Arcs in the Frequency Range 0.1-1000 MHz

Lifetimes of free-burning arcs in air