Telemetry & scanning

How far will a telemetry signal travel? Ie. how close to the tracks do you need to be with your scanner before you're able to pick up a telemetry signal? Thanks.

that all depends on how low you got your squelch and how far the train and or location of the transmitter is from you.. it could be miles or it could be less than that all depending on squelch and location.

1. what is a telemetry signal? [RR]
2. what frequency is it on?

a. the (VHF) answer, anyway, is, line of site + 3-10 miles, good generalization.

The EOT (457.9375) has very short range because it is a low profile antenna on the box on the rear coupler.

You can usually get better reception on the locomotive HTD (452.9375) since the antenna is on top of the locomotive and it is closer for a train moving toward you. This assumes a 2-way "telly" is in use and not just a one way EOT.

These are low power, short range devices, since they only need to communicate from one end of the train to the other.

If you use a scanner, you usually need to lock it on the channel since the packet transmissions are so brief the scanner is likely to miss it if it is scanning a lot of channels or the squelch setting is tight.

Kinda off topic , but I realize EOTs are low power. If 2 trains are passing each other, or in a yard together, is it possible for them to read each other's signal from the EOT or is each EOT system "tied" with a specific reciever?
Tied meaning like a PL system or something like that.

Each EOT has a unique digital ID code that is dialed in on the HTD and then the EOT is "armed". This establises a connection between those 2 devices and all data packets from devices on other trains are ignored. With the brief duration of the data packets, many pairs of devices can share the channel without interference or false operation.

If you are familiar with ham packet radio or computer LAN protocols, this is similar. Many digital devices share a communications link with multiple communications between specific pairs of devices going on with each pair having its own virtual direct connection.

LOL. I've heard crews saying the EOT is armed. I always thought that it meant that the air was up and ready to go, not tied to the HDT. Thanks for the insight.

The other significance of "armed" is that the EOT is in communication with the HTD so an emergency brake application can be made by the EOT on command from the HTD.

If the EOT fails to periodically receive signals from the controlling HTD after it is armed it sends a "FRNOCOM" (front to rear no communication) message to the HTD to warn the emergency application feature is not available. If it does not recover, the train must operate under safety restrictions (grade and speed) for failed telemetry.

anyone have enuff info on the packet format and what is sent ?
and is it worth unbuttoning? might be a fun thing to try, or record and try to unbutton..
but if all it contains is an ID, it might not be worth the time..

As for as I know, it contains the ID and information about the air pressure. If it's just the ID, it still could be worth it, especially in territory where they don't call signals or have ATCS. Hear a databurst, so you get out to shoot the train. After it passes, you keep hearing the databursts...until one of them turns out to be a different ID. Time to get out and set up again!

The only thing the data burst contains is EOT ID number, air pressure, armed signal for rear dump valve.
The unit does not send a train id or so, the locomotive reciever has to be set for EOT number ID for it to work.

EdM wrote:anyone have enuff info on the packet format and what is sent ?
and is it worth unbuttoning? might be a fun thing to try, or record and try to unbutton..
but if all it contains is an ID, it might not be worth the time..

There is a software program ATCS Monitor that decodes EOT as well as ATCS. But, don't know if it is worth bothering with for EOT since the only data is what has been described above.

http://www.atcsmon.com/

There is a software program ATCS Monitor that decodes EOT as well as ATCS. But, don't know if it is worth bothering with for EOT since the only data is what has been described above.


Yeh, that is what I thought. I still haven't got up the ambition to unbutton the aircraft stuff, and that is supposed to be really neat, so I guess the tail end stuff can stay in the closet.. Ed