Southern Road Channel 2

[D300]

Its has been a few years since I last lived on any ex-SR lines. When I did in the 80s and 90s, NS made use of road channel 2, an unusual duplex of two separate frequencies for a single back and forth communication. Now days when I fan I end up on N&W lines most often.

160.830 and .245 were the freqs. if I remember the numbers correctly.

Of the times I have been on ex-SR lines most recently I do not remember seeing -- seeing as in noticing the numbers on the scanner -- this channel in use. Is this channel still in frequent active use on the ex-SR lines?

D300

[E.M. Bell]

Ch 2 and 3 are still very much in use. While you wont hear much on them on some lines (like the CNO&TP) they are used a lot on lines that are TWC instead of CTC. Case in point, the Louisville Districts, where the dispatcher is almost constantly on Ch 2 give out track authorities, ect.. 

[Fly Device]

Does anyone happen to know the background on the Southern's choice of full-duplex? Do or did any other roads use full-duplex?

I can understand using separate channels for road and dispatcher communication on busy lines, but allowing the dispatcher and crew to talk to one another simultaneously does not seem useful in a railroad context. It's not a phone conversation. You wait for "over" before you talk. Maybe I'm missing something.

[Backyard]

  That is exactly the point...two road channels, one for talking, the other for receiving.

This allows for instant communication without having to wait, in case a condition changed the current orders.

If one signal "dropped-out," the other allowed instant alert of the missed communication.

[Batman]

NS Ga Div lines and CT Dispatch use channel two all the time.

[D300]

I can not answer the why, but to the crew it is almost invisible. On the radio you select an input and output freq, such that the radio reads say -- 0808 -- (for talking and receiving on the same AAR freg) and 0814 for talking on a duplex. Once the radio is selected, it is like every other conversation.

Yes, other lines have it but they are rare.

My only guess is so high powered radios, like yard towers, don't overpower lower powered radios like engine radios in critical communications like reading back trainorders and now TWCs..

D300

[Backyard]

  There are repeaters installed today, because of the use of the radio trains in the past, all along the routes.

Topographic features of hills & tunnels used to cancel-out radio signals, as well as sun-spots(magnetic interference), etc.

If I know the Southern Railway System, this was tested to death, and therefore approved as the standard radio setup.

Braswell Mt. in Northwest Georgia, was the only tunnel on the line(now daylighted), but it was at the top of the grade, on what's now the North Atlanta District.

Even though things have improved now, with repeater towers at both sides of tunnels, etc, you still cannot give on the spot replies to the dispatcher on the same channel.

[E.M. Bell]

D300, you nailed it. Southern and then the NS do that for the simple reason that avoids channel bleed over and interference that could cause problems with the crew hearing what the DS is saying, and the DS hearing the repeat back.

There are a lot of lines where verbal authority is the only means of traffic control, and it has to be done perfect every time...lives are at risk if not.

[Fly Device]

If one signal "dropped-out," the other allowed instant alert of the missed communication.

Fair enough. A crew is in the middle of a lengthy readback, gets something wrong or is momentarily walked on. Dispatcher doesn't have to wait for him to finish to tell him to stop and try again.

D300, you nailed it. Southern and then the NS do that for the simple reason that avoids channel bleed over and interference that could cause problems with the crew hearing what the DS is saying, and the DS hearing the repeat back.

Understand. Perhaps the full-duplex played a role in letting Southern get by with using the same set of frequencies systemwide (if I'm not mistaken), rather than alternating channels for adjoining dispatcher territories as is sometimes done on other roads.