atcomsystems.ca/forum Forums Other TDM Phone Systems 1A2 and Comkey Telephones & Systems Greetings and a Request for Some Info on How to Setup Small Keyset System

"Instead of just going off hook and completing the loop to get Dial Tone, you (the PBX) have to apply a momentary ground to the Ring side of the line. The CO recognizes a request for DT and returns a ground on the Tip side of the line. The PBX recognizes the confirmation signal and connects a load to the circuit, completing the loop. When the distant end hangs up, the CO opens the Tip side of the line and the PBX recognizes the disconnect signal and hangs up the line."

OK, another question (questions rather) if I may. What exactly do you mean by Central Office? Like the telco HQ?

Second, how can you "return grounds"!? I know that across the live tip (+) and ring (-) connectors you have a certain amount of negative voltage (-48?), which is made possible by "putting ground on the positive" (another concept I'm confused about). How can you put ground on the positive? Very confused!

The central office is a mechanical or electronic switching system that provides dial tone phone service to your particular geographic area. In most cases, it is housed in a nameless, faceless building. This building may house multiple switches, including ones that belong to other phone service providers.

With regard to your question about grounds: Each phone line is usually delivered to the premises over a perfectly-balanced twisted copper pair. Unlike electrical wiring, the only time that either of these wires is associated with a ground is through an intentional and temporary connection. In the previous descriptions, the CO switch and the customer's PBX "talk" to each other by "touching" one wire or the other to a true earth ground. A lot more communication than voice occurs over that copper wire pair, and it happens very quickly.

Telco power plants have the positive side of the output grounded. This confuses many people because they are so familiar with automobiles, which are predominately negative-ground.

Most vehicles, cars, trucks, farm tractors, were originally positive ground until the mid-50s. In other words, the frame was "hot", not grounded. That is why in rainy weather the battery on the car would go dead as the insulating tires would get wet and drain the battery. Positive ground.... :nono:

Thanks Ed and Ken. You're all a great help!

I sincerely hope that you wrote that with your tongue in your cheek. I have never heard anything quite as preposterous.

There is no "ground" in a car. There is + and there is -. They are floating, and they have no reference to the earth. If you need proof, take an ohmeter and go from either side of the car battery to the earth. Tell us what you measure.

I remember the positive ground (frame) on the early tractors especially. Wasn't an earth ground, but it was still called ground.

I'm with Bill and Ken on this one Arthur. It's not a true "ground" but it's what it was always called.

At least that's what we always called it in Brooklyn.

Sam

I've never heard it called anything but ground. Negative battery terminal to car frame.

The interrupter is a 10Vac motorized device that has cams and contacts that deliver interrupted electricity as the cams turn. Steady generator and steady lamp battery are connected to the sets of contacts respectively, and the output leads deliver interrupted generator (1 second on/3 seconds off) for common bells, and interrupted lamp battery as follows:

60 ipm / 50% break for lamp flash ("LF"). Used to indicate an incoming call.

120 ipm / 5% break for lamp wink ("LW"). Used to indicate call Hold.

"Flutter" is a lamp supply that has an extremely rapid interruption rate (I seem to recall that it is 5 interruptions per second) that is not provided mechanically by standard interrupters. It is provided by an electronic timing circuit, and is used to indicate a call that has been placed on "I Hold" (pronounced "eye hold" -- the "I" stands for the person who placed the call on Hold, like "me").

I-Hold is a feature that is used in a large office (today they are called call centers) where it is is imperative that the person answering the call be the only one who can place it on Hold and retrieve it from Hold. This is important for a business that wants to ensure that an agent is the only one to talk to a caller, so that the caller is not inconvenienced by having to start his story all over again when the first agent places him on hold and goes to get some information.

Generally, I-Hold could only be offered on Call Director type telephones, with replaceable 598-type key strips. The first key strip usually has a red Hold key, and 5 clear (uncolored) line keys. Each successive key strip has 6 uncolored line keys. An 18-key Call Director (630 series) has three key strips, of 6 keys each, and a 30-key Call Director (631 series) has 5 key strips.

For I-Hold, the first key strip is replaced in the field with a special key strip that has a red Hold key, followed by a green I-Hold key, followed by 4 line keys.

To place a call on "regular" hold, the user presses the red Hold key as usual, and anyone who has access to the Held line can go back into the connection.

To place a call on I-Hold, the user presses the green key, and the line being placed on Hold can only be accessed by that person. The line lamp flutters at the "I" person's phone, and stays steady (or winks, depending upon the type of service requested by the customer) at all other appearances of the line.

This feature can be provided these days through software on electronic key systems. I am only vaguely familiar with electronic key systems, predominately the Samsung ones. On a Samsung Prostar system, if the user presses the red Hold key once, he puts the call on Hold. If he presses the Hold key twice in succession, he puts the call on "I-Hold." (I think they call it "priority Hold" or something like that.)

If you would like to chat about the various 1A, 1A1, and 1A2 systems and their oddities, feel free to email me to set up a phone call. It's easier to ramble on and on about this stuff by voice, rather than by teletype, like this.

AWWWW-----the good old days....and if the battery was low/dead....grab the crank. The starter just spun the engine to get the magneto firing....same for the crank.