Can anyone point me to a telephone line tester circuit on the web somewhere? I am looking for something that will indicate whether the line is alive and whether the tip and ring signals are reversed. Tried doing a Google search, but came up with ready, made ones. I have enough junk around here that I figure I can build one for nothing.
if you got a multimeter and a phone you can start testing. check the voltage across the pair, should be 48VDC in US, 60VDC in europe. place a 600 ohm resistor, 5W across the pair and measure the current should be 20 to 40mA (holding current) rw
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The usual way of doing this is to use a bicolor LED that glows read with one polarity and green when the polarity is reversed. You just put a resistor in series to limit the current. I think the ones I have usre 3.3k, maybe more if the voltage is high. the max current for a phone line is 60 mA, so it would be wiuse to put 3 or 4 diodes in series in each direction to absorb any excwess current above 20 mA or so. But the dissipation of the resistor may be more than a half watt. So use a couple in series or a 1 watter.
BTW, if you plug one of these into a wall jack, the polarity will be correct, but the modular line cord flips the polarity so that it's reversed at the phone jack. So you have to know where you're testing.
More info is on comp.dcom.telecom.tech newsgroup.
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They must have changed it then... but somehow I doubt it. See
Anyway, if the tech reversed the main frame jumper... the wire colors mean nothing. You need to check the polarity with respect to earth. The normal polarity is;
The 'A' leg (or TIP) is connected to earth at the exchange and therefore the 'B' leg (or RING) will be -ve wrt to the 'A' leg (or TIP).
Connect a digital voltmeter between both wires of the line. When the meter reads -52V the red lead will be connected to the 'B' leg (or RING) and the black lead will be connected to the 'A' leg (or TIP).
And I could provide the URLs I referenced that claim otherwise.
But I agree that it isn't very relevant anymore anyway. Seems likely that the contractors that work on phone wiring these days don't have the same attention to detail as the first couple generations of telephone technicians. Hard to distinguish brown with orange stripes from orange with brown stripes in the bottom of a dark manhole. :-)
And it doesn't really matter anymore anyway. All modern phone equipment will operate properly regardless of the polarity. The stuff that doesn't isn't properly designed or assembled. Note that it was (is?) common to reverse polarity to indicate certain things like call completion.
Ahhh... wait a moment. I understand you're referring mainly to "modern" phones, but I still take issue with that statement!
The older Bell System (Western Electric) phones from the 70's- early 90's are most certainly "properly designed and assembled" (as evidenced by their amazing service life -- my key system has been going, more or less continuously, for 20+ years), but earlier TouchTone sets will not dial out with reversed polarity.
In fact, it was common practice among telephone installers to flip the polarity on the connection to sets that the owner did not want people to be able to dial out on.
I've not heard of RP being used to indicate call completion (perhaps someone else has?), but I will say that it is common for most central offices in the U.S. to drop the line battery altogether for about two seconds, if a phone goes off-hook and you don't do anything for 30 or so seconds.
The reason for this dates back to the first key telephone systems, developed in the 40's. If a line were taken off-hook, and then immediately put on hold, or if a caller on hold hung up and the line went back to a dial tone state, AND the hold bridge failed to release, it could tie up common equipment at the CO.
That battery drop I mentioned above will force the hold bridge at the customer's end to release, thus clearing the line. Even the most modern of electronic CO's do the battery drop thing to this day.
This has been your Bell System trivia for today. We now return to your regularly scheduled Schickelgruber.
Dr. Anton Squeegee, Director, Dutch Surrealist Plumbing Institute
(Known to some as Bruce Lane, KC7GR)
But as time went on, apparently it got harder to find good help. So it became cheaper to put a 50-cent bridge rectifier in the dialpad circuit (which they actually did), than to pay the tech to debug why the old phone worked and the new one didn't.
Yes, I was assuming that >99% of the readers of this thread will not have access to polarity-sensitive, early TouchTone equipment.
When they converted the Waikiki exchange to ESS, half the subscribers lost the ability to dial. Seems there were a lot of reversed reversals in the middle of the wiring, and the installers just flipped the leads till it worked. :)
Even into the 80's I had no true DTMF service, though the telco charged for it. They put a tone to pulse converter on each line. "Beep"-Dit-Dit-Dit...
This was also a time when you couldn't dial 800 numbers from hawaii. Most frustrating when some companies had ads with only 800 numbers on them.
They had to pay for all those individual line tone->pulse converters!
Same in the Redlands (CA) exchange. As late as the mid-70s the DDD (Direct Distance Dialing) was implemented in Strowger relays. (Reputed to be the first DDD in the General Telephone territories.)
You could dial San Bernardino (opposite side of the freeway) and wait for 5 minutes of "tick-tick-tick-tick...". Or just call the Operator and tell her you call didn't go through. Some of us didn't even bother to try dialing first.
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Been there, done that, got the T-shirt. Damn installers ruined a lotta times and I get stuck with straightening out their abortions.
I had pulse dial, and got my 300 baud Smartmodem, with DTMF. I used the TT on it once, and the Pac Hell bastards tried to contact me and make me pay for the service. They wanmted a buck twenty a month!! For something that benefitted them more than the customer! Finally the Calif PUC came to their senses and made the telcos give everyone DTMF for free, so we could all call the 'voice jail' systems without having to switch from pulse to tone after making each call.
Yeah, lotta good that does the customer. Like when your number is
I had a Rat Shack TRS-80 Model 100 with the modem that dialed at 20 PPS, and it worked okay, too. Twice as fast as regular pulse. I believe it still would work today, too.
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I worked at LLU from 69 and moved to OR in 78. Back then, they still had
9-10 operators with cord sets handling incoming calls (no direct inward dialing). And the campus system was switched in a large room full of Strowgers and twenty-four 2v wet cells the size of refrigerators.
Heard that after I left LLU became so peeved with the Redlands CO (GTE) that they put up a private microwave and got service from across the freeway (Colton, PacBell).