Anyone know what kind of "telegraph channels" are still supported today? I thought they were all obsolete and removed some years ago. (I recall seeing tariff announcements to that effect.)
In this month's Verizon phone bill, there is a notice of private line rate increases. Most items seem to be contemporary digital services, such as "DS1", "DDS", DSND, B-channel, D-packet, and VOI varieties. There are also various "analog channels" and a separate group of "voice grade channels" listed.
But there are some "Metallic Local Channel", "Metallic & Telegraph Grade Local Channel", and "Telegraph Grade Local Channel" groups. Would anyone know accurately what they are? There's a "Metallic transmission function" at 77 cents in high density areas, and $13.37 in low density areas.
I thought in telephone usage the term "metallic" refers to when they replaced single-wire--ground-return transmission with two-wire transmission 100 years ago. Also, "telegraph" meant very low bandwidth--50 to 100 baud--Baudot Teletype lines.
There's also a group called "Program Audio". Would this be high grade lines for radio station usage?
Lastly, there's a group called "Secretarial". Is this answering service?
Thanks. Public replies, please
***** Moderator's Note *****"Metallic" means metal: in other words, it means a circuit using direct current signalling on copper pairs instead of one that employs tone-based or digital transmission of some sort. They were used for central-station burglar alarms, such as those provided by ADT.
Burglar alarms used to be wired in series, since they used McCulloch loops for signalling, just like municipal fire alarm boxes: each station had a different code, and when the alarm was triggered, it would break the loop in a prearranged pattern to tell the central station which node was sending. At the central station, the signal was recorded on paper tape by a register that either marked the tape with a pen or punched holes in it for each pulse: this is exactly the same way Morse designed the original telegraph system.
When I joined Ma Bell, we were taught to troubleshoot burglar alarm circuits by using a Volt-Ohm-Milliammeter at the frame, checking from one pair to the next to find an open circuit, because they were wired with _SINGLE_ wires from the ring of the first pair to the tip of the next, and so on until the last pair's ring lead would be connected back to the first pair's tip.
I always loved working on BA's: it was a sure-fire four-hour overtime, because the pairs were _never_ in the same order as the circuit card called for, and there were often additional stations that had been added or existing ones disconnected, without proper record keeping. That meant that I and a cow-orker had to "pull" the leads from each pair to the next, correct the record, test the (newly documented) pair, and then pull to the next pair.
In the early 80's, the company switched to using "burlar alarm multiples", which were just frame blocks that had been allocated for connecting the pairs in a McCulloch loop together: the back of the block was wired to provide the ring-tip, ring-tip connecitons, and ordinary pair wire was run from each cable pair to the front side. This simple innovation meant that I could find an open pair by "running the block", i.e., by just moving the tips of my pliers across the lugs so as to short each pair in turn, changing four hours of overtime into (at most) four minutes of troubleshooting. When the open pair was identified, it was only a moments time to wire a short across it until the cable was fixed.
Metallic circuits are fairly rare these days: New England Telephone dropped them years ago, ostensibly because of high maintenance costs: however, I think it was really because too many companies were using them for data circuits. A sophisticated telecom manager, faced with a choice of paying thousands per month for a T-1 line or a few dollars for a metallic "burglar alarm" circuit, would just buy some line-drivers and make his own T-1. Of course, we testmen had a lot of fun "repairing" such lines when we found them: my favorite trick was to "Box change" them from a single pair onto two defective pairs that had each had only one side open, thus providing a "metallic" circuit that was utterly useless for data. Customers who complained of noise would hear me recite a speech about the lack of a noise specification in the metallic alarm tariff.
Yeah, I know, but I was young.
ADT and other central station providers changed over to computerized alarms and modems as quickly as they could during the 80's: the new equipment provided more data (building temperature, sprinkler pressure, individual "door ajar" info, etc.), and was also _much_ more difficult for burglars to bypass. The pairs assigned to metallic McCulloch loops were converted to low-speed data, and moved from BA-multiple blocks over to two-wire audio bridges. In the few cases where metallic circuits were still provided, mostly because of "grandfathered" circuits contracted to municipalities, we would wire the local cable at each end to special T-Carrier channel units that simulated McCulloch loop operation.
Program Audio lines are for radio stations, as you surmise. As a senior testman, I did a stint on the "Radio Board": we thought nothing of spending an entire day equalizing a pair so as to attain flat frequency response from 300 to 15,000 Hz., even for a one-time remote broadcast lasting only a few hours. The tariff called for it, we delivered it, no questions asked.
I'm not familiar with Secretarial service, but I agree it's probably for TAS.
Thanks for the trip down memory lane!
Bill Horne Temporary Moderator
(Please put [Telecom] at the end of the subject line of your post, or I may never see it. Thanks!)