EMC Test Standards Recommend Fibre Optic Links

Why use a Fibre Optic Link?

Introduction

A Fibre Optic Link (FOL) has many advantages over conventional galvanic conducting cables, such as coaxial cables and this has lead to their wide use in many diverse areas. The main benefits include immunity to interference, very low loss and electrical isolation.

Most FOLs are designed for a specific application, i.e. a digital data link, and can not readily be reconfigured for an alternative use. However there are many applications where it would be beneficial if a coaxial cable could be directly replaced by a FOL. In fact many EMC test standards, i.e. DO-160, ED14, Def. Std. 59-41, IEC, CISPR, EN, etc., recommend the use of a FOL to ensure isolation and signal integrity. There are also many other test and measurement applications that can be greatly enhanced by the use of a FOL.

For the above reasons PPM have designed a range of analogue FOLs that can be used as a direct coaxial cable replacement. These links not only afford all the advantages of optical fibres but also include many useful features such as multiple inputs, signal amplification and adjustable input attenuation, all of which can be controlled via RS232 or IEEE488 interfaces.

2. Why Use a Fibre Optic Link?

· EMC test and measurement

· HIRF testing

· Shielded effectiveness / attenuation measurements

· Insertion Loss / coupling assessments

· EMP and Lightning monitoring

· Detected HPM measurements

These applications exploit the following three benefits of a Fibre Optic Link:

· Immunity to Electromagnetic Interference

· Minimal Signal Distortion

· Electrical Isolation

The following sections describe the main advantages of FOLs and highlight some typical applications.

2.1 Immunity to Electromagnetic Interference

Unlike conventional cables, optical fibres are immune to electromagnetic interference they therefore make an excellent alternative to coaxial cables when routing through a dirty RF environment is required.

Interference will reduce the signal to noise ratio of a system and this in turn will reduce the dynamic range and lower the sensitivity. The use of a FOL in a dirty RF environment will therefore maximise the potential signal to noise ratio and sensitivity of any measurement system.