A thin film electron source comprising a substrate, a lower electrode formed on one main face of said substrate, an insulation layer formed in contact with said lower electrode and an upper electrode formed in contact with said insulation layer. Accordingly, in multi-hop communication, frequency efficiency is improved by not using different RF frequencies between a control channel and service channel, and applying a control channel and service channel through the TDM method, and the channel efficiency is improved by WAVE channel switching. An exhaust cam assembly is operated to move an exhaust valve between a first position a second position.