Phone line through an XLR cable

Discussion in 'General Electronics Chat' started by electronewb, Aug 24, 2012.

  1. electronewb

    Thread Starter Member

    Apr 24, 2012
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    I need to use an XLR cable to carry the signal from a phone jack How can I wire the RJ-11 to a 3 pin XLR? I will use pin 2 and 3 on the XLR but what pins or colors from a phone cable carry the signal on a phone line?
     
  2. DMahalko

    Active Member

    Oct 5, 2008
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    The center pair is line 1, the wires out around those are line 2. You only need two wires in a twisted pair for phones to work.

    It is the same for an 8-wire Ethernet cable, which also works to carry telephone signals. The center pair is line 1, and the two wires out around those are line 2. The two edge wires are each grouped as pair rather than using the symmetrical arrangement of the four center wires.

    Since balanced cable is also a twisted pair, you should be able to connect the two center phone jack wires to the twisted pair in the audio cable and have it work okay.


    Though, the XLR cable may have a different impedance so sending telephone audio may not work for very far. I don't know the technical details for this part.

    Also, I don't know if telephone pairs are considered balanced but it is possible that they are, due to the twisted pairs and only two signal wires.
     
  3. electronewb

    Thread Starter Member

    Apr 24, 2012
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    OK thanks Also is there a +,- on the center pair or both wires carry the signal? usually pin 2 XLR is the hot (+) and 3 is the cold (-)
     
  4. #12

    Expert

    Nov 30, 2010
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    + and - don't mean anything unless you tell them to. A telephone line starts out with +48 volts while waiting. A "ring" is about 105 volts RMS at maybe 20 to 45 HZ. When the receiver is connected, the polarity reverses to a low voltage, like about -18 IIRC.

    For Dog's sake, do not give them a path to earth ground. Even a meg to ground and you'll get a buzz that is significant.

    All this is antique information. I bet you can find it on the internet.
     
  5. gerty

    AAC Fanatic!

    Aug 30, 2007
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    And the off hook voltage is about 6v.
     
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  6. electronewb

    Thread Starter Member

    Apr 24, 2012
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    Interesting I found 2 phone cables in a pile of junk that I have and both cables only have 2 wires a red and a green!!! I thought for sure all phone cords were 4 wires!!!!
     
  7. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    I remember phone wires as two wire - a red and green. The other two wires were for two line phones. If you got red and green reversed, touch tone dialing would not work. All dialing today is touch tone. The old way of dialing was called pulse dialing, which would still work with the wires reversed.
     
  8. electronewb

    Thread Starter Member

    Apr 24, 2012
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    Is the red and green an official standard? I found 2 more cables one has green and yellow wires and the other cable has red and black
     
  9. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    I haven't read all the posts in this thread, so what I write may be somewhat redundant. But to answer this question, most subscriber wire drops contain 4 wires, which are normally organized into 2 pairs: a red and green pair and a black and yellow pair. One pair is required for each line, and the red/green pair is usually the first one used in the cable. If there is a second line, it uses the black/yellow pair.
     
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  10. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    What you have are line cords for individual telephones, which only require two wires. If you were to look inside the jack on the wall, you would find a 4 wire cable as I described in my previous post.

    Some line cords do have four wires, and are required on dual-line telephones.
     
  11. electronewb

    Thread Starter Member

    Apr 24, 2012
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    On a side note anybody can use that DC to be use for something else? Like powering up a lamp in your living room???
     
  12. #12

    Expert

    Nov 30, 2010
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    Don't try. There are only a few milliamps available and the phone company will get really irritated with you.
     
  13. electronewb

    Thread Starter Member

    Apr 24, 2012
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    I wasn't gonna try I just thought about it.... free electricity :D
     
  14. absf

    Senior Member

    Dec 29, 2010
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    But when the phone rings, the ringing current is gonna blow you LED in mS.

    But many use its current to power a FM bug transmitter. That I think only consumes 1 or 2 mA.

    Allen
     
  15. kagana8

    New Member

    Jan 22, 2012
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    you use only 2 twisted wire to connet
     
  16. kagana8

    New Member

    Jan 22, 2012
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    can you show us this configuration in photo?
     
  17. JMW

    Member

    Nov 21, 2011
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    Red/Green are line one. Yellow/Black line two. As another pointed, out do not go to ground. The lines are balanced 600 ohms.
     
  18. electronewb

    Thread Starter Member

    Apr 24, 2012
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    So 2 wires.... one is talk and the other one is listen?
     
  19. #12

    Expert

    Nov 30, 2010
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    No. Two wires form a circuit. An old fashioned telephone pair has several duties and they change across time. The 48 volt DC is a "waiting" signal. When your telephone makes a connection, the signal is reversed in polarity and reduced in voltage to supply your dialer. If the interaction starts with somebody else's phone, the pair is used for a ring signal of over 100 volts AC. When a connection is made between two parties, the pair is used to convey audio signals.
     
  20. dataman19

    Member

    Dec 26, 2009
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    Telephone (ie: Telecommunications) wiring is standardized in a tip/ring/sleeve configuration. Red is "Tip", Green is "sleeve", and Yellow is "Ring". The black wire is ground. (Note sleeve is common, but not ground).
    ...
    This is the original balanced pair configuration where the + is Red and the - is green (the balanced pair). When a balanced line 600-Ohm transformer is connected its center tap is connected to the "yellow" (sleeve) wire in the Telephone Central office (most are still connected this way too).
    ...
    The old Bell system used the following protocols"
    ...
    The 48VDC talk battery is applied to the center tap of the 600-ohm center tapped transformer (+ goes to the center tap, and - goes to the ground. This way the 48VDC talk battery is even across the red/green wires in the pair. (Note: This is also where the term "phantom" power comes from).
    ..
    When a telephone is on-hook (hung up and not in use) the center tap is isolated and there is no current drawn across the pair. There are .1 uF electrolytic capacitors placed in-line with the phone ringer (one for the red and one for the green wire) - this provides an AC path for the 20Hz 105V ring signal to ring the bells. The capacitors also keep the 48VDC from energizing the bells, so the bells require AC - the 20Hz, to ring.
    ...
    When the phone is taken off-hook, these caps are switched out and the hook switch connects the common to the sleeve - causing the phone to draw power. At the central office a relay/shunt is activated that causes a warbling dial tone to be placed across the line. This is an indication that the phone line is active and that a number sequence can be dialed.
    ...
    Should the phone be ringing (because the 105V 20Hz intermittent ring tone is being received, and passed to the bells) the ringing stops when the phone is taken off hook and drawing talk battery and receiving dial tone.
    ...
    The number sequence determined whether the call was a local call, a regional call or a long distance call. The phone numbers were like IP addresses (In fact the magic jack system uses IP addressing in their numbering schemes).
    ..
    Phone lines always have and are two-conductor pairs (red and Green). The old yellow wires were used to source the party line call rings. In the late 1960s the idea of using the yellow and black wires in a telephone quad for a second line was adopted for inside premise wiring.
    ..
    The reason a four wire phone cord has a center pair (red and green) and two outer wires (one on each side) was due to the old telecomm standard whereby the black was the ground lead for the phone handset chassis, and the yellow was the common sleeve (only used for party/Duplex line signaling - whereby the red lead of the ringer could be placed on the yellow wire, giving an alternate ringer position. In this configuration two phone number could share a single pair and one each phone would have its own ringer. This also tied up an additional pair - but the trade off was that three pairs could support six phone (doubling the phones on any given rural cable).
    ....
    XLR are balanced audio cable. While telephone circuits may be touted as 600-ohm circuitry, the telephone lines are actually 900 ohm. XLR cables are 600 Ohm 3-wire cables. The reasoning is that 48VDC traveling down a balanced 900-ohm pair yields a smaller signal loss that 48VDC traveling down a 600-ohm balanced cable pair. The DC component in the telephone signal gave it longer runs with less signal loss (the voice was superimposed onto the DC component, and was equal in magnitude across each wire - ie: Balanced. Should noise be induced by inductance, what ever, it generally was not uniform across and wire in respect to the center common, and therefore attenuated at the destination device. Since the phone hybrid (the active device in the phone) combined the voice component across the pair into a hearing and speaking component, it effectively shunted imbalanced noise to common and eliminated most unwanted noise.).
    ..
    Not with standing, phone lines did in fact have noise issues, but given the 10,000+ foot cable lengths from central office to individual phones, it worked quite well for its time.
    ..
    Repeater coils were nothing more than capacitive/inductive loading coils that effectively balanced the lines and neutralized stray capacitance (a characteristic of long cable pairs) and realigned the inductive properties to bring voltage and current lags leads into proper balance. They actually gave a better that 3db gain of voice signals over cable noise - which effectively made the voice signal louder.
    ....
    Now you know why there are four wires is telephone station wire. But the cable coming from the pole was only two wires (the ground was in fact the earth ground - which explains why all the phone DEMARCartion (Entry Points) had ground rods installed. Not only did the ground rod provide a path to ground from the gass line lightning shunts at the telephone entry point - it provided the common signal ground back to the central office. The pair was essentially a floating energized circuit, but the ground signal path was the common reference that made the balanced cabling work. In the XLR the 3rd wire is the common signal ground, since XLR Balanced pairs do not involve an active earth ground - the 3rd wire provides a direct common interconnect.
    ....
    Hope I haven't bored too many. I know it is a lengthy post, but there was a lot to cover.
    ..
    Yes telephones are considered 600-ohm but there are impedance mismatches involved when XLR (true 600-ohm) cables are used for telephones (which actually use 900-ohm cabling .
    ..
    Note: in the long haul system the telephone circuit is actually four wire. The transmit pair is at -16 dbm0 and the receive pair is at +7 dbm0. This gives the ability of the facility to attenuate the receive signal to 0 dmb0 to allow for cross patching (both send and receive is at zero dbm0 - the transmit/or send is then further attenuated down to -16dbmo so that it can be transmitted by radio to the distant end. This was the basis that allowed repeaters to receive signals and send them down the cable to the central office without expensive and power hungry line amps. Since the Radio output was at +7dbm0, and the radio transmit input was at -16dbm0, there was a level budget of 23db. This allowed for long cable runs from pone radio site to another, and even the ability to run cable from a microwave site down the hill, or downtown to the telephone central office..
    ...
    Incidentally, these were the standards of the old Tropospheric Scatter(150+ Mile Range) 800-900MHz Radio systems of the 60s and 70s. The 800MHz and 900MHz bands were gobbled up by the Cellular Systems, which resulted in the elimination of Tropo Radio Links worldwide in the late 1980s. Tropo radio Sites used multiple receivers capoable of receiving minute signals. Tropo Transmitters were capable of +100db and even +200dB signal strengths, and the receivers were capable of using signals as low as -102db. Hence the extremely long ranges, aided by the reflective properties of the Troposhere at 800-900MHz, naturally.
    ..
    Add the 600+ Telephone channels that were stacked in groups of 12-channels, and further combined in Supegroups of 10 or more groups, and then Master groups of up to five supergroups and you have a 600-channel wideband radio set. Each channel was naturally 4-wire (two send and one receive wires - wouldn't work any other way).
    ...
    The early adoption of four wire telephone sets was a dismal failure - since four wire phones effectively cut existing cable plant capacity in half. Still, in the 70s and 80s Ma Bell did offer four-wire phone service for some business and corporate customers. In fact Basic Rate ISDN (BRI - one quad/line w/2-phone lines) and Primary Rate ISDN (PRI - One quad/line with 24-Phone lines) were and still are four wire, because of the nature of how the lines communicate. They are also the analog equivalent of digital service - since each channel is 64Kbs and each BRI/PRI uses a 16Kbps control channel.
    ..
    But I am digressing into a book and have exceeded the intention of my original reply.
    ..
    Needless to say. Phone lines "are" one pair/two-wire. But now you know where the four-wire telephone systems originate from, not the local phone lines, but the long haul phone lines.
    ...
    Dave
    Phoenix, AZ
     
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