DTMF Tones

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dic

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Listening to the Lancaster/Tehachapi feed on railroad radio.net and am hearing DTMF (phone) tones.
What purpose do they serve?

Thank you
Dic
N1XBA
 

KiloEcho4ZDJ

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In this area Norfolk Southern has a phone patch on their repeaters and you can hear the tones. I believe CSX uses a tone when crews are trying to contact the dispatcher.
 

k6cpo

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Some Maintenance of Way (MOW) vehicles won't trigger automatic crossing gates. Those gates are triggered by manually entered DTMF tones transmitted by the radio in the MOW vehicle. The tones usually correspond to the milepost number of the crossing.
 

KiloEcho4ZDJ

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When the train crew is trying to call the dispatcher they will transmit a tone. The closest trackside repeater will pick it up and will then alert the dispatcher. Dispatch will then connect to that repeater and communicate with the crew.
 

PMJ2kx

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I've heard someone dial a 10-digit number, and then be greeted over the air with "We're sorry. If you would like to make a call, please hang up and try again." :) I think that was one of our Class IIs but I'm not 100% sure, as it was on a feed...

Like others have said, I always hear DTMF for either toning up the dispatcher or operating crossing warning devices (gates, signs, etc).
 

Mojaveflyer

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Here in Colorado the railroads use them for accessing local repeaters to call the Dispatcher. UP (and former DRGW) has area transmitters that cover large areas. BNSF uses repeaters at every siding (or every other one) that are much more local transmitters. The BNSF dispatchers east (Brush Sub) and north (Front Range Sub) will usually identify the transmitter they are talking to the train on. Different four digit tones will bring up the individual siding radio. UP has mountain top transmitters for the Denver Metro Area, north on the Greeley Sub, and south on the Joint Line. On the line going east to Limon and Kansas (Limon Sub) they use some more localized transmitters. BNSF has more widely spaced transmitters going south on the Joint Line to Pueblo.

Hoe that helps a little...
 

burner50

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The normal use of DTMF tones is to notify the dispatcher that someone needs to speak to them, or to control certain switches (never heard of them activating crossing circuits).
 

PMJ2kx

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(never heard of them activating crossing circuits).
Dick Samuels, owner and operator of the Oregon Pacific Railroad, explains that here for his specific shortline:
Altamont Press Discussion Board :: Discussion :: Re: Oregon Pacific Railroad's GMD-1 in Snow Action - Video link

At about 24:29 in the video they are discussing, you can see the sticky that shows the specific tones for each street (only two, in this case). :)

https://www.youtube.com/watch?v=ro8u61gF2SI#t=1469
 

burner50

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dsw760

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Back in the day railroads used to use PBX (Private Branch Exchange). Basically it was a phone-to-radio-to-phone interface where a special code is dialed to access the PBX, and then the phone number is dialed all using DTMF tones. CSX used to use it to call signal maintainers, yard masters, ect.
 

KDOXF

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Also used to have detectors repeat transmissions. Not sure what number they key in but on many installs on CSX, the detector will respond "Rebroadcast" and then repeat the last transmission.
 

burner50

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Also used to have detectors repeat transmissions. Not sure what number they key in but on many installs on CSX, the detector will respond "Rebroadcast" and then repeat the last transmission.
Many BNSF detectors still have this functionality.
 

Eng3ineer

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Back in the day railroads used to use PBX (Private Branch Exchange). Basically it was a phone-to-radio-to-phone interface where a special code is dialed to access the PBX, and then the phone number is dialed all using DTMF tones. CSX used to use it to call signal maintainers, yard masters, ect.
Good friend of mine and my family was a new signal maintainer back in early nineties . I still remember the look he gave me when asked if his supper was good last night and told him what all he had. He asked how did I know that. Told him everything he said over the radio comes across any scanners or radio's. He turned RED the next night he worked when he called his wife first thing said right off was that he was on the radio phone. LOL He did that every time he called her until they phased out using the PBX
 

jgroenke

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Regarding the DTMF tones Heard on Tehachapi Feed

The three digit DTMF tones are in fact used to light a light and sound a tone in the dispatcher's pod at the Harriman Center (or BNSF's dispatch center in Tx) to let them know somebody needs to talk to them. They don't normally listen to all the chatter that goes on and for good reason:

Depending on the territory's size, and terrain (mountainous or flatland or both) they could have upwards of 10 to 20 different Base Stations with which to talk/listen to the trains. (they may need 20 different sites just to be able to talk to everywhere on their district)

Thus all those receivers couldn't all be active at the same time putting audio into his speaker or headset or all he would hear is mush.. some receivers would just barely be hearing the intended signal and that poor noisey signal would cover up the excellent signal that the closest receiver is providing.. And of course there could be trains switching or talking to MOW or detectors going off many receivers away and they would all add to the jumble of different audios. And then there's the delay caused by the phone or data circuits used to back haul the radio communications back to the dispatch center. So they need a way to filter out and be selective as to where they are talking and receiving.

So the solution is: each Base station has a DTMF tone decoder that has a unique code to trigger it. The train crews know what that code is. When they need to speak with the dispatcher, they need to pick the radio site (they call them 'towers'), then they send the 3 digit tone and wait for the automatic answer back tone which is a long single lower pitched tone that tells them the base station has heard their tones, understood them, and the dispatcher has been signalled.

When the dispatcher can talk to the train (he may be talking to someone else far way in his district for instance) He'll acknowledge the call request which then connects the audio from the toned up receiver to his speaker and/or headset and they can then have their two way conversation with the person who just signalled him. When the dispatcher is done he puts that base station back into mute (so he won't hear anything from it until the next time he selects it or it's toned up by a train or MOW).

The train crews can also send a different set of DTMF tones to a detector and have it play back the details of the last test. This is so they can confirm what they think they heard.. Also, some older detectors will send out a tone that will ringdown the dispatcher (open up his speaker so he can hear the defect report) if it is a serious one. However, they are getting away from that practice now a days as all the detectors' audio output are being recorded in 'the back room' and they had the ability to play back the tape to listen to what's been recorded. Matter of fact ALL the radio communications are being recorded from all the receiver sites and of course the dispatcher's side of the conversation. But that's nothing new... been going on for decades.

Probably more than you wanted to know, but there you go...

Jim G
www.railroadradio.net


Listening to the Lancaster/Tehachapi feed on railroad radio.net and am hearing DTMF (phone) tones.
What purpose do they serve?

Thank you
Dic
N1XBA
 
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burner50

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Better late than never, I guess, but here goes anyway.


The three digit DTMF tones are in fact used to light a light and sound a tone in the dispatcher's pod at the Harriman Center (or BNSF's dispatch center in Tx) to let them know somebody needs to talk to them.
Yes, that's one use, as previously discussed in this very thread.


They don't normally listen to all the chatter that goes on and for good reason:
A good dispatcher will listen to as many radios as possible. In fact, many times while fueling, the fuel truck reports clear, and the dispatcher will go ahead and hang me a light before I can even get him toned up. He's monitoring the radio.

So the solution is: each Base station has a DTMF tone decoder that has a unique code to trigger it. The train crews know what that code is.
That's true in some situations. On the UP, all towers in a certain area have the same tone, and often when you tone the dispatcher, you'll hear multiple towers tone back. I've been on the BNSF before when trying to reach the dispatcher tone up a certain tower, and if the dispatcher is unavailable, I'll be out of range before he comes back to talk to me.

The train crews can also send a different set of DTMF tones to a detector and have it play back the details of the last test. This is so they can confirm what they think they heard..
Almost, but again, you're speaking in absolutes, and on some major railroads, that simply is not true. In almost all cases, if you miss the report, or it is otherwise unintelligible, You don't have an option to have it read back to you. You simply tone up the dispatcher and he either pulls up the detector results, or calls the desk in charge of inspecting detector readouts, and returns with the results a moment later.



It's far more accurate to simply state that DTMF is used on the railroads as a way for users to operate equipment, be it switches, crossings, remote radio's, detectors, or simply to notify people that they're needed. Sometimes, it's even an automated safety system emitting the tones.

For instance, when in remote operations, the chestpack worn by the crew has an accelerometer inside that can sense when the pack is not being worn properly. An improperly worn chestpack can indicate a crew member has fallen or become injured, and the engine will dial 911 on its own to alert people of a possible injury on its crew.

By saying that DTMF is only used in those very specific scenarios is facetious and misleading.
 

jgroenke

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Sorry for not being clear, and I didn't mean to be facetious or misleading. I was trying to answer back to the specific question posted about the DTMF tones being heard on the Tehachapi Area stream which I host.

I totally agree with you that what I was posting should not be construed as being applicable in all areas but I was trying to tailor my response directly to the poster's question about what the tones he was hearing do, and I wasn't trying to speak generally as there are many other posts in this thread that addresses other ways DTMF signalling is used.

Wasn't the most helpful first posting, was it....
 
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