Abstract. This paper reports the transmission measurements made on 40 km of graded-index fibre which have been cabled and installed in operational ducts for use in 8 and 140 Mbits−1 systems. Extensive loss and bandwidth measurements were made at all stages of the programme, both before and after cabling and also in the field using two mobile test vehicles. The problems of obtaining meaningful and reproducible measurements are discussed and the stability of the measurements between the various cabling and installation stages is assessed. The results have been analysed in conjunction with additional laboratory measurements and a number of important propagation effects have been brought to light.
