  We present the theory for the signal formation in a multi conductor detector
with cylindrical geometry and long length. There exists electromagnetic wave
propagation along the large dimension of the detector. The system is equivalent
to a multi conductor transmission line. The treatment is in the TEM
approximation. Each conductor is fed by its current source which is the same as
in the case of small size detectors. A simple example is given for a long
length Monitored Drift Tube (MDT). One could apply the result to a long
micromegas-type detector or any long microstrip detector, ignoring propagation
that is transverse to the strips.
