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A study of intermodulation interference due to non-linearities in metallic structures

Lui, Pak-Leng (1990) A study of intermodulation interference due to non-linearities in metallic structures. Doctor of Philosophy (PhD) thesis, University of Kent. (doi:10.22024/UniKent/01.02.86014) (KAR id:86014)


Intermodulation products are spurious frequency components generated when two or more signals mix in devices with non-linear characteristics. In multifrequency communications environments such as communal antenna sites, intermodulation products generated by active devices (transmitters and receivers) and passive components (metallic contacts and conductors) can cause serious radio interference. The interference caused by passive intermodulation products is a well known phenomenon and is sometimes called the 'rusty-bolt' effect. This study is directed towards the characterisation, detection and location of external passive intermodulation interference sources at land mobile radio sites used by the UK Emergency Services. The thesis describes the development of computer-controlled passive intermodulation product measurement facilities. The laboratory and field measurement work investigates the parameter related to the generation of intermodulation products. The measurements concentrate on the lower order products and results are given for combined input powers of up to 63 W at 150 MHz. The types of test conditions and samples used are similar to a typical radio site environment. A review of previous investigations related to passive intermodulation is presented. The various non-linear mechanisms at metallic contacts are described and the most dominant one is identified. Some analytical techniques for predicting intermodulation signals are considered and the theoretical results based on a power series model are compared with measurement results. The basic principles of detecting and locating non-linear metallic contacts are explained. Experimental studies of audio and radio frequency detection techniques are conducted and strategies for detecting and locating external passive intermodulation interference sources are outlined.

Item Type: Thesis (Doctor of Philosophy (PhD))
DOI/Identification number: 10.22024/UniKent/01.02.86014
Additional information: This thesis has been digitised by EThOS, the British Library digitisation service, for purposes of preservation and dissemination. It was uploaded to KAR on 09 February 2021 in order to hold its content and record within University of Kent systems. It is available Open Access using a Creative Commons Attribution, Non-commercial, No Derivatives ( licence so that the thesis and its author, can benefit from opportunities for increased readership and citation. This was done in line with University of Kent policies ( If you feel that your rights are compromised by open access to this thesis, or if you would like more information about its availability, please contact us at and we will seriously consider your claim under the terms of our Take-Down Policy (
Uncontrolled keywords: Electromagnetic compatibility
Subjects: T Technology > TK Electrical engineering. Electronics. Nuclear engineering
Divisions: Divisions > Division of Computing, Engineering and Mathematical Sciences > School of Engineering and Digital Arts
SWORD Depositor: SWORD Copy
Depositing User: SWORD Copy
Date Deposited: 29 Oct 2019 16:24 UTC
Last Modified: 10 Dec 2022 06:45 UTC
Resource URI: (The current URI for this page, for reference purposes)

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