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How long can a telephone extension-cord be?

Discussion in 'Electronic Equipment' started by wylbur37, Aug 13, 2005.

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  1. wylbur37

    wylbur37 Guest

    Recently, at a Radio Shack store at the telephone accessories section,
    I noticed that telephone extension cords were available in lengths up
    to 25 feet (but I didn't notice any that were longer).
    Is that because 25 feet is the longest you can go before there's a
    significant loss of signal strength?

    And what about people who access the internet via 56K dial-up?
    For them, how long can the extension cord be and still have "clean"
    transmission for error-free downloads?
     
  2. 18,000 ft?
     
  3. Charles P.

    Charles P. Guest

    A phone cord is just more wire that connects to the phone company's wire
    that travels miles to get to your house. So you can make a cord about as
    long as you want.

    The technical details alter a bit, in that the typical phone cord (and a lot
    of home wiring) is straight conductors (i.e. side by side) but the cable
    outside tends to have pairs twisted together. The twists in the pairs of
    wire helps to block some interference (that is why computer cables have much
    tighter twists, too).

    A 56K modem can also work for a very long distance, again, interference can
    creep in, and that may slow the signal down. There are many other issues
    that will affect the modems too, so that they rarely get real 56K speed.

    Office type phone systems have more restrictions on the length of wire
    because those types of phones are doing more things and using more voltage
    that your average "single line telephone".

    Charles
     
  4. Joseph

    Joseph Guest

    You need to shop at Home Depot or Lowe's where you can get 50 foot or
    100 ft modular extension cords. When I was renting a room there was
    no wiring for phone and I used one of these 100 foot extensions to go
    directly into the network interface box and I was using DSL!
    - -
     
  5. speed.

    "56k" modems are limited by law to 53k, and seldom get that even that
    high.
    That's not necessarily true. Some PBXes use the same 48V as the central
    office, some use less - only 24V. Some use in-band signaling so they
    don't need any better wiring than the regular POTS telephone. The
    system I work on is digital, so it has a restriction of 2000 feet, but
    that's not necessarily true for other PBXes.

    One thing you might want to consider is that running phone lines greater
    than 25 feet is that they get trampled on, tripped over, and get in the
    way of other things. Radio Shack doesn't sell longer cords because
    there is little demand for them, and they sell only high demand, high
    volume stuff. You can buy flat 'silver satin' modular cable in lengths
    up to 1000 feet or more, and make your own with the crimp-on connectors.
    I regularly make up custom lengths from 2 inches to a hundred feet or
    more. But it's risky having things on the floor that people might trip
    over.
     
  6. However, the one thing to be careful of with long extension
    cords is that they must be *twisted* *pair* cable.

    Such extension cords are also commonly available in what is
    called "flat satin" type cable, which has parallel conductors
    that are not twisted. That might work if the extension is used
    with a telephone, but it should be avoided for data, whether it
    is a DSL or a v.90 modem.

    I wouldn't use anything longer than about 6 feet of flat satin
    cable to a modem.
     
  7. David Lesher

    David Lesher Guest


    Not even close. Ma did a loop plant survey back in the 1970's
    and one operating company reported a 100,000 ft loop....
     
  8. "Wolfgang S. Rupprecht"
    Old telephone lines that came out of a central office had no electronic
    equipment to help them out, so a dwelling that was, say, 5 miles (26,400
    feet) out of town had to have loading coils on the line every 6k feet.
    People don't realize it, but there are still a lot of those lines in
    use, even in cities and towns.

    If a phone line has loading coils on it, then it can't be used for DSL
    at any length. The loading coils have to be removed.
     
  9. That's 'only' 19 miles. If two cities were farther apart than that,
    then they would use inter office trunks that were longer than that. Of
    course, later, it was cheaper to use carrier or pair gain equipment than
    to put more copper in the ground. So later you saw a lot of T1
    circuits, which have repeaters every 6k feet. Then came fiber optic
    cable and everything changed.
     
  10. Found this one: 16 miles, back then longest in Calif. Another website
    says longest in the world, which might have been possible in 1882, but
    I'd say state is a safer bet.
    <http://www.chaffey.org/community/dailybulletin/1990s/1996/1996_11_14_ch
    affey_garcia_house.html>


     
  11. Interesting. Do you know if they had to use the more electrically
    shielded pairs in the center of the cable to get any sort of distance
    or was any old pair that the rats hadn't chewed on too much good
    enough?

    -wolfgang
     
  12. Don Bowey

    Don Bowey Guest

    That's not necessarily true either. PBXs with analog ports typically use
    "class A" port equipment, giving them a range of about 200 Ohms as I recall.
    A class C PBX port (used for off-premises stations) looks very similar to a
    CO POTS line interface which will reach to about 1800 Ohms.
     
  13. "Wolfgang S. Rupprecht"
    Standard telephone cable back in the '70s was pulp insulated, and for
    that long, it would have to have loading coils every 6kFt. Or if the
    line was installed decades before that, they might have had special
    loading coils.

    But this is not to say that it couldn't be something else. In order to
    get service to farms, some telcos used fenceposts to support the
    insulators, and strung something like 10 gauge copperweld wire along the
    fenceposts. Or if it was to a location where they didn't want to build
    a CO out in the boondocks, they may have used some kind of remote
    station to serve a small community. It's funny, but the droids back in
    the service centers still think that a line is copper, even tho it's
    mostly over pair gain such as fiber. Well, I guess you could blame it
    on their test equipment, which probably can't tell the diff. :-O
     
  14. Bill Janssen

    Bill Janssen Guest

    In Nevada we had a long line with carrier equipment part way (30 miles)
    and then 15 miles of
    Open Wire. The OW was ( I think) number 12 copper weld. We also had a
    circuit of ten mile single wire
    with ground return . So, not all circuits were on cable.

    Oh for the good old days.

    Bill K7NOM
     
  15. Terry

    Terry Guest

    In order to
    Getting a bit far from the original question.
    Right on. In this province of Canada we used "open wire" even for some
    subscriber loops in rural areas. Typically it was Number 8 hard copper, each
    pair spaced 12 inches, on ten pin crossarms.
    Stories abound about long, long lines with up to, or more than, 100 phone
    customers on one pair across farming areas of the Canadian prairies and
    western USA! If anybody had an emergency (such as barn fire) others on the
    line would respond to a general ring.
    Copperweld was/is copper coated steel wire.
    Just looking up Number 8 solid copper wire; noted it has a resistance of
    approx. 3.3 ohms per mile; so that is 6.6 ohms per 'Loop" mile.
    Assuming that a typical dial office loop could be around 1000 to 1200 ohms,
    that's a theoretical subscriber loop distance of, say 174 miles! And with
    those old fashioned carbon granule microphones, powered local by two 1.5
    volt cells, with quite a high output without any tubes or transistors it
    would probably work quite well, despite the transmission loss over that
    distance. And anyway some other party listening on that multiparty line
    could repeat the message down the line!
    I know we had one such line with 14 customers, each paying 1.75 per month
    which included the telephone directory and new local batteries whenever
    needed.
    Terry
    Trouble with those rural lines was that they were usually joint use with
    power lines. resulting in all kinds of induction hum, atmospheric noise
    pickup and various power switching transients.
    PS. I think I've seen 50 foot 'extensions' in a local dollar store.
     
  16. CJT

    CJT Guest

    Anything over a few hundred yards and you probably ought to think about
    things like lightning protection -- not your typical "telephone
    extension cord."
     
  17. Guest

    The 25' cable is probably what best fits on the sales display hook!
    Sure there are in-line couplers so the sky is the limit for length.
    For a long cable run rather than having the cable strewn about, why not
    use standard quad station cable, connect it to one jack, fish, staple
    or otherwise make a neat job and run to the other jack. Even if you
    live in a rental, it can easily be done. Remember there is space
    between the wall-to-wall carpet and the baseboard. Many a low voltage
    wire has been tucked in there to get around a room unseen.
     
  18. Rich Grise

    Rich Grise Guest

    Before my laptop died, I had a 100' Home Depot MEC that I'd cut the
    RJ-11s off and put on RJ-45s, and had TCP/IP from the LAN to my Motor
    Home. :)

    Cheers!
    Rich
     
  19. Bill Bowden

    Bill Bowden Guest

    Is that because 25 feet is the longest you can go
    If the limit were 25 feet, you would have a problem connecting your
    phone to the telco which may be several miles away.

    They usually use 48 volts to supply 20mA of current in series with your
    phone. The phone is about 600 ohms and drops 12 volts at 20mA which
    leaves 36 volts that can be lost in the line. If you use 22 gauge
    copper wire, the resistance is about .016 ohms per foot, and 36 volts
    at 20mA is about 1800 ohms, so the maximum length would be 1800/.016 =
    112500 feet or 21 miles. A larger gauge will increase the distance.

    -Bill
     
  20. Don Bowey

    Don Bowey Guest

    The phone is not 600 Ohms DC resistance. A tone dialer phone is 330 Ohms
    DC.

    Don
     
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