Steamal-there was a post on the previous version of this site regarding an experiment the New York Central did in the early 1920s for locomotive to caboose communications. I also unearthed some photos a couple of years ago of some Union Pacific equipment, equiped for radio communications in that same time period, that I presented at a meeting of my local amateur radio club.
I think the drawbacks of HF communication and the power requirements of vacuum tube technology did not allow for effective (and widespread) use of radio communication. World War II provided the impetus for the development of FM communication and smaller, more shock resistant types of radio. The post-war period, when dieselization was rampant, coincided with the adoption of radio by more railroads.
I'll see if I can uncover those photos and provide a link, if it is still active. In the interim, I'm sure there are more knowledgeable folks who frequent this forum that can provide a better answer than I have.