[Scan-DC] Information about railroad radio system?

[John Pak]

Hello,

I have started to listen to more railroad radio trafic.  Can any one tell me a good comprehensive source that explains how railroads radio systems works?  Basically I am looking for railroad radio listening 101.  Forexample, I have been listening to 160.9200 which I understand is the mtrack road for this area.  What does ctac mean?  Where is ctac?  Thanks for any help.