Telephone Tip/Ring Question

OK, it's not my turn, but "on hook" means it's hung up, the current loop is open circuit, and "off hook" means it's in your hand, and the current loop switch is closed, and current is flowing.

Hope This Helps! Rich

Sorry, I just noticed my typo. I meant to say *why* is on, or off, hook called on, or off, hook? (not what it does).

Of course, we could also ask why is it called "hung up" when you put down the handset (or push end call)?

IIRC, step didn't reverse the line, but I don't remember the final stages of the connector that well anymore, so it is possible it did...

Charlie Former SxS Equipment Maintainer

I always thought that line-reversal (or applying a voltage) was used to hang up a call you didn't originate. ...Jim Thompson

Jim, did you finally get some useful info? Assuming that Verizon and others for traditional analog telephone service are following the old Western Electric (Ma Bell) standards, then the on-hook DC voltage between Tip and Ring should be nominally 48 VDC. If you measure (either Tip or Ring - I don't remember which one) to earth ground you will also see 48 VDC since one side of the central office battery is connected to earth ground. From an AC (voice frequency) standpoint both Tip and Ring are balanced to earth ground (for hum reduction) with a nominal line/set impedance of 600 ohms. The AC and DC aspects of the line are kept isolated via chokes and/or repeating coils, which are required in a common-battery (as opposed to local battery) telephone system in order to prevent the shorting out of the audio by the central office battery.

Now in "ancient" times two-party line ringing was accomplished by connecting the phone's ringer from Tip-to-earth ground on one subscriber's set and from Ring-to-ground on the other subcriber's set. This also had to be wired appropriately on the central office's ringing equipment. Connecting subscriber set ringers in this manner adds a very slight amount of hum due to the unbalancing of the phone line (but not much due to the ringer coil high impedance).

AFAIK all ringing these days is bridged (ringer connected Tip-to-Ring) so ringing-to-ground would probably not work. This is also worth remembering if you ever desire to hook-up an antique phone (e.g. a WE type 500 or 2500 set) to your phone line and find the ringer non-operative (unless you want it that way). The ringer should be connected to the incoming phone line red and green wires with no ringer wire connected to the yellow or black one. Sincerely,

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

Charlie is correct Jim. Polarity reversal indicated a call was answered.

Perhaps you recall the early days of third party long distance carriers... The tone pad on the calling phone was often disabled, presumably by the polarity reversal, which made it impossible to enter the long distance codes for a third party carrier. Personally, I carried a pocket dialer which stored touch tone sequences in a calculator size device. I would hold it to the phone transmitter to complete the call.

In the days of fiber optic links, a polarity reversal is ancient history.

Jon

--- news://freenews.netfront.net/ - complaints: snipped-for-privacy@netfront.net ---

The past... it's all coming back to me ;-)

The house has only 3-pair, but if I keep careful track of the wiring, this will work:

TIP1-----------o------------------o | | RINGER1 PHONE1 | | RING1----------)------------------o | | | TIP2-----------)------o-----------o | | | | RINGER2 PHONE2 | | | RING2----------)------)-----------o | | | | | | TIP3-----------o------)-----------o | | FROM BLOCKERS | NO PHONE LINE CONNECTION OR PHONE | | RING3-----------------o-----------o

The blockers will pass ring on legitimate calls only... all 800 numbers go bye-bye ;-) ...Jim Thompson

Right, they are at frame ground potential at the central office! And, there is no reason to be sure the two lines are from the SAME CO! Ours are not. One is from the real CO, the other is from an RT a couple blocks away.

Jon

Nope. That's been automagic for years. Hang up for X seconds. Step may not have had it; XB surely did. It came into being because the Jesse James Gang's successors would call all the bank's numbers, locking them up, THEN rob the place.

What's going away/gone is CPC; Calling Party Control. It momentarily dropped loop current on the CALLED line when the caller hung it.

It was there to handle the abandoned call, where you called Microsoft Support and were put on hold for 2 years; or Bell Repair, for that matter. It came into being with the 1A key system "HOLD" feature, but also helped on answering machines.

But that's almost all gone; many remotes (SLC-types) have no way to interrupt the loop current. Amazingly, the ARRIS ATA's used by ComCrap and other cable carriers do seem to have it.

.......................Bell's

Unless it was a long rural loop, which was where you found many party lines... Then the hum was an issue.

NotBell used tuned ringers; there were FOUR plans, as I recall:

I can no longer remember all the names....

Fail....I bet.

Why not just leave the ringers on the third pair? You can either use one side to ground, or bias: a ringer [not a tweedledeedle, a ringer..] can be set so DC bias one polarity to inhibit it from ringing. Pick up a Lorain Products Sub_Cycle to make the

Naaaah! That works. Trace it out. ...Jim Thompson

Digikey was selling a small ring generator module, the last time I looked.

That's no fun; a SubCycle will make a nice hum, and it's 100% short circuit proof; an elegant piece of magnetics...

It's heavy and wastes energy. It's big, and the ones I have laying around have nice, sharp corners. Not everyone likes things to hum mindlessly. If it didn't bother anyone, there would be no need for kill filters on usenet. :)

There was one in every 1A2 phone system, and I've junked about 100 of them.

I've read all the answers so far looking for mentions of hum and this is the first I've seen. As I recall, there is an earth ground rod at the entrance, but the installer can tie it to either line of the balanced pair to minimize hum.

Ring voltage used to be about 90 volts - can you use a bridge rectifier feeding a voltage comparator to detect it, then some dc circuit to ring.? 48 volts is normal idle, the phones are low enough inpedance to drop it near 0 when off hook, but the ring voltage emulates the old hand-cranked generators with about 90 volts AC out.

Then again, I've never worked for a phone company and haven't tried this stuff since the 70s.

Alan

This is a pretty neat group.

J.B. Wood:

As far as I know the Tip should be to ground (only at the central office's side) and the Ring at -48 VDC. This was due to prevent corrosion and ion migration.

The off-hook voltage should be between 6 and 10 V.

No! If you ground tip or ring anywhere except via the line card, the imbalance will destroy the line.

Both T & R do have a overvoltage protector that shunts to local ground, and that is tied to the building/power ground (MGN - Multi Ground Neutral).

Party line ringing disturbed this balance, but in theory the L-C ringer circuit limited the imbalance.

There's a ground rod, yes, but neither tip or ring are 'tied' to it on the subscriber end.