Abstract:
Power line carriers are used throughout the world by electricity supply utilities
for telecommunication purposes. These systems are unique as they have
the ability to provide communication over distances that can exceed one
hundred kilometer without the aid of repeaters. The power line acts as the
transmission medium.
In the research the occurance and effect of third-order intermodulation
products on the signal-to-noise ratio of power line carriers in Eskom, were
investigated.
Power line carrier manufacturers do not provide adequate specifications
about the behavior of their products with regard to the generation of
intermodulation products under operational cond itions. This information is
required by designers of communication systems utilizing power line carriers
to ensure optimal performance of such systems.
Detailed specifications might also be valuable in the identification of
equipment suitable for specific applications. Power line carriers are often
connected to a mismatched load and an important aim of this research
project was to determine the effect of a mismatch between a carrier and its
load. A test unit, consisting of a bandpass filter and a variable load
impedance, was developed to facilitate measuring the generation of
intermodulation products under simulated load conditions. The accuracy of these measurements was also investigated.
An important conclusion that can be made on completion of the research is
that a mismatched load does not impact much on the amplitude of third-order
intermodulation products at the two-wire side. However. it has been found
that load mismatching has a big influence on the trans hybrid loss. This loss
is an important factor in the final signal-to-noise ratio at the receiver.
