I'm way over here on the west coast (KC area), but most metro areas have some railfan sites that might help you understand what you're hearing.
Here are a few "railfanning St. Louis" sites I Googled up:
St. Louis Railfanning - Hotspots (unknown date)
http://www.gregariousrailfan.com/files/St_Louis.pdf (2013, has map)
St. Louis Railfan Guide (1996!)
Most of the time these will just have the frequencies, and not the details on PL or other tones. Also, some of them are kind of old, but I have found that railroads usually don't change things around
too often.
A lot of people here probably already know this, but if you hear an engineer identify their train as the "NS 1234", that doesn't necessarily mean it's a Norfolk Southern train - it just means it happens to have an NS engine on the front. If you can catch the dispatcher, they will almost always identify with the accurate name of the railroad.
The feds have a map with all the big railroads, but it's not working for me at the moment. No frequencies, but it does have the mileposts.
https://fragis.fra.dot.gov/GISFRASafety/
For UP only, a (now retired) engineer posted his own versions of track charts for most of UP's system. Archive at
http://web.archive.org/web/20160330215920/http://fogchart.com/FOGCHARTED.htm . The St. Louis area ones don't seem to have radio information, but they do have the mileposts, station names, etc, that might be interesting. (The radio information on those charts is usually the AAR channel number, and not the frequency, but you can look it up.)
BNSF apparently doesn't mind about having their employee timetables online, as long as they are at least 10 years old. These will have the radio frequencies as AAR channels, station names, mileposts, and other goodies. For the St. Louis area, you want the Springfield division:
BNSF Timetables – Phase 4 – FOBNR.ORG