Hi Randy,
Horn commands should be repeated every 100 ms. That will give you a sustained blow as long as the commands keep coming.
If you have access to the LCS WiFi module, the free LCS WiFi Monitor Windows program would give you an easy way to see what commands the Lionel Remote is generating. TMCC commands may be enough for your application and these can be injected directly into the Lionel command base's serial port.
Sending Legacy commands requires an LCS SER2. But again, from reading your description of the desired operation, I think TMCC-style commands should be sufficient.
(http://www.lionel.com/lcs/LCSproducts/page/index.html)
Rudy
