ECN Forum Forums General Topics of the Trade General Discussion Area Taking readings from a telephone line?

Just wanted to add some specs for POTS (Plain Old Telephone Service)

**** "(NOM)" = Nominal, or Typical; "(LIM)" = Limits ****

On-Hook Voltage:
48 VDC (NOM), 4 - 105 VDC (LIM),

Off-Hook Voltage:
6 VDC (NOM), 4 - 105 VDC (LIM),

Operating Current (Also Known As "Loop Current"):
25 ma (NOM), 20 - 120 ma (LIM),

Telephone Set Resistance:
300 Ohms (NOM), 100 - 400 Ohms (LIM),

Subscriber Loop Resistance:
0 - 1300 Ohms (NOM), 0 - 3600 Ohms (LIM),

Loop Loss - In dB (deciBels):
8dB (NOM), 17dB (LIM),

Distortion (THD):
- 50dB

Ringing Frequency:
20 Hz (NOM), 16 - 60 Hz (LIM),

Ringing Voltage (RMS):
90 VAC (NOM), 40 - 130 VAC (LIM)

Ringing Current (RMS):
20 - 50 ma

Maximum REN (Ringer Equivalency Number):
5 REN (total of all sets not to exceed 5)
-suffix "A" devices ring @ 20 Hz,
-suffix "B" devices fing at any Hz.

Bandwidth: 3 KHz (180 Hz to 3.2 KHz)

Signal to Noise Ratio (SNR): 45dB (apx.)

Signal Levels - Average (at Tip / Ring): -9dBm (normal speech), +4dBm (peak speech)


DC Supply Is Positive Earth Grounded (the "+" side is grounded), so system is normally referred to with respect to Ungrounded Polarity - such as:
" -48 VDC "

"TIP" = " + " Polarity, "RING" = " - " Polarity.

Color Code (Simple Examples):

"Level 1" / "JK Cable":
TIP = Green, RING = Red

Multi Pair Cable (i.e. Level / CAT 3, CAT 5, etc.)- 4 Pair Cable Listed Below in first examples:

Pair #1:
TIP = White / Blue color band (stripe),
RING = Blue / White color band,

Pair #2:
TIP = White / Orange color band (stripe),
RING = Orange / White color band,

Pair #3:
TIP = White / Green color band (stripe),
RING = Green / White color band,

Pair #4:
TIP = White / Brown color band (stripe),
RING = Brown / White color band.

If Cable Has 5th Pair:
Pair #5:
TIP = White / Slate color band (stripe),
RING = Slate / White color band.

Pair Colors Passed The 5th Pair - Upto The 25th Pair:
(swap "White" listed above for Pairs #1 thru #5 with color listed below)

Pairs #6 thru #10: Red,
Pairs #11 thru #15: Black,
Pairs #16 thru #20: Yellow,
Pairs #21 thru #25: Violet.

I can add more if needed, or include Telephone relavent data (such as this list, plus more advanced details) in the Technical References section.

Let me know what sounds good - and if anyone can assist with documents.

Scott35 S.E.T.

As I said, we were college students. We called collect!

Scott35:

Thanks for the data--please do post what you can. I very much appreciate the reference material you (and others) make available!

pauluk:


Yes and no

What I am trying to do is to figure out where an imbalance (unbalance?) might be. That would be more along the lines of capacitance rather than resistance, right? I guess that's more of a job for a TDR (with a pro operating it...) rather than a DMM. Either that or one of these ...

Well, I took some readings just out of curiosity and one was quite interesting:

KHz, ring-to-ground, was 770.

That's WABC talk radio, the station that is heard on the phone line

Scott,

I started out my career installing burglar/fire alarms and we had one type of a system called a "BA" alarm. The central office would send out 130 volts DC over the phone line to our control box. The readings you got back told us if the alarm was off/on/ or in alarm. That 130 VDC would really sting if you got nailed by it.

Harold