Railroads don't use repeaters and in some instances, railroads may use a pair of frequencies for train to dispatcher and dispatcher to train. The Motorola Spectras found in locomotives are capable of selecting separate TX and RX frequencies. In this case, you'd have to scan between both frequencies to hear both sides of the conversation.
Depending on terrain, I can usually pick up locomotive radios from about 2-3 miles away with the cheapo rubber duck antenna on the my handheld scanner. Going through my 2m antenna on the car, I can receive locomotive radios from 10-20 miles away. I regularly get yard chatter from Tilford yard in Atlanta just a few miles from my home, which is about 15 miles straight line distance between the two.
The dispatchers talk on one frequency to the trains, and the trains talk back on another as has been stated.Is it common to only get one side of a conversation? I have no problems hearing the dispatchers. I just can’t seem to pickup the other half. Could it be because my antennas are mounted inside? Thoughts?