An 800 Mhz Approach to Underground Data Communications

As part of a communications network designed for a computer automated rail haulage system, a UHF data channel was developed to exchange information between stationary wayside computers and driverless locomotives. The data link uses modified 800 Mhz FM equipment, and voice frequency FSK modems. The 800 Mhz channel frequency was selected after evaluating available wire and radiated wave approaches, including trolley wire, induction loop, leaky feeder and free space propagation. A major consideration was the relatively high EMI emitted by the locomotive chopper controller. The allocation and control of UHF channels is similar to cellular techniques in the reuse of UHF frequencies to cover different areas separated from one another by sufficient distances so that co-channel interference is insignificant.