The types of transmission systems which today are available for long
distance transmission of large numbers of telephone circuits are those for coaxial
cables and radio links. The number of circuits is increased in both cases in
step with development in technique.
Radio links have for several years been able to transmit 600 telephone
circuits per system. and are now being designed for 960 circuits.
The capacity of the coaxial cable systems is now being increased from
960 to 10800 circuits per system. Parallel with this increasing of capacity the
problems as Cross-Talk and Interference in this systems become more important.
The problem of Cross-talk between different systems on the same route
can be overcome nowadays using relatively simple means.
The main problem in both cases is the interference which arises within
systems at the many points of amplification. Interference ocurs there just as
inevitably as friction in a machine and it is a difficult technical problem to
design equipment in such a way that high transmission quality is obtained.
The types of interference which accur most often are «babale» and «noise»thermal
noise and itermodulation noise.
In this article emphasis has been placed on the noise specially intermo,
dulation noise and its relation with number of channels and repeaters in the
system. At the end for practical using of what is written in this article and also
for using C. C. I. T. T. recommendations about noise a repeated line is designed
for open-wire, as an example.
)