n7maq wrote:
As you are hearing there are two tones, the first one (this could also be a DTMF string) the second one will be the base station's transponder to acknowledge the call. If the train crew does not here the transponder then they know they need to tone the dispatcher again.
Jim
Yea, I've been listening a little closer over the past few days. I occasionally hear the mobile DTMF strings, followed by the base station with the "acknowledgement" tone. Most of the time, I guess I don't hear the DTMF input, because the trains are likely out of range - but the base station is not.
Thanks for the clarification, all.
Brad.