Oh yea I forgot to distinguish between mid train DPUs vs end of train DPUs. So the locomotives have a program to be EOT's if they are run as end of train DPUs so therefore the EOT would be using the DPU's antenna for EOT transmissions
So the EOT number would be the number of the DPU? If the end of train DPU is the same unit as the EOT except with additional EOT payloads would be attached to the DPU payload packets right because it would be broadcasting not only its power fields but also the brake pressure so this would all feed into the same central computer. I'm not 100% familiar so please correct me
So if a train was using a DPU as end of train there would be no EOT transmissions on the usual EOT frequencies? And if it was a mid train DPU the EOT would be broadcast along with the DPU freqs so thats 2 freq data transmissions among the unit. so That would be how you'd distinguish if a train was rear DPU or not by the lack of EOT freq transmissions as its included with rear DPU tranmissions?
They don't act as an EOT. An End Of Train Device serves a specific purpose. A DPU serves some overlapping functions, but covers far more than what an EOT would do. If there is a rear DPU, there is no EOT unless there is an EOT deadheading for some reason. So, once you realize that they're completely separate things, you'll have an easier time understanding.
Not all circumstances dictate the use of an EOT, and their use is declining. There needs to be a marker on the rear so that other trains can verify that the train they're meeting is complete and intact. An EOT is a common modern way to accomplish this, but it can also be accomplished with a lantern, a person riding the rear, a DPU, a fusee, etc... Something to indicate that the train is complete and there isn't random cars left somewhere on the main line.
As far as what is contained in the data for a DPU, there is all sorts of things. A DPU can be operated almost completely as any other engine independent of the lead engines by radio control. As far as how to determine which you're hearing I can't say that I have ever tried to monitor DPU data. It's been several years since I left the railroad, but I believe DPU data is also on UHF.
The most surefire way to determine if there is an EOT vs a DPU is to look at the rear end.