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Telephone line amplifier

Discussion in 'Electronic Design' started by Anthony C Smith, Jun 30, 2004.

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  1. does anyone have the schematic or a link for a telephone line amplifier for
    the speech line of a standard telephone?
    The type I am looking for is a two wire line in and two wire line out (the
    type telcos put in the cable in the street) when reaching outlying areas.
    regards

    Anthony
     
  2. Dbowey

    Dbowey Guest

    Anthony posted:
    << does anyone have the schematic or a link for a telephone line amplifier for
    the speech line of a standard telephone?
    The type I am looking for is a two wire line in and two wire line out (the type
    telcos put in the cable in the street) when reaching outlying areas.
    You are asking for something that does not exist. The 2-wire repeater (E6
    repeater for example) exists as Central Office equipment, but none were placed
    out of a C.O. environment.

    Don
     
  3. J M Noeding

    J M Noeding Guest

    would you like something simple like a negistor? Philips made it in
    the 70's, but was not much success when a circuit had several
    different cable types

    In the other way, you must use 2W/4W hybrids and separate amplifiers
    for the different directions and somewhat limited gain, dependent on
    the line balance

    -jm
     
  4. Bubba Jones

    Bubba Jones Guest


    I recollect that some telcos had pole mount enclosures for remote
    areas, equipped with Lorain SRM803 & LLE 121 modules to extend loop
    length and VF gain. However, it has been many years (& beers) since I
    was involved with outside plant equipment.
     
  5. Alan

    Alan Guest

    British Telecom had some "negative impedance" amplifiers in the late
    60's. These were based on (if I remember rightly) a "T" attentuator
    network where the 3 resistors were replace by gyrators to produce the
    negative impedance, and therefore gain. I can't remember now what the
    gains were but the amps had to be carefully tweaked for the line
    impedance.

    As somebody else noted, you can use a pair of hybrid transformers to
    convert a 2w to 4w and back again and use two separate amplifiers, one
    for each direction. Again the hybrids have to be matched to the line
    impedances to get the required rejection.

    A third way may be to use an echo canceller type of circuit.

    And if this is for your home phone why not complain to the telco about
    low levels?

    Alan

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  6. Dbowey

    Dbowey Guest

    JM posted:

    <<
    would you like something simple like a negistor? Philips made it in
    the 70's, but was not much success when a circuit had several
    different cable types

    In the other way, you must use 2W/4W hybrids and separate amplifiers
    for the different directions and somewhat limited gain, dependent on
    the line balance
    The E6 repeater was a "negative impedance" *2-wire* repeater - no hybrids. It
    was very successful and was found in large quantity in Bell Central Offices.
    GTE also had an excellent version of the "2-2" repeater. They both used
    optional networks to enable them to balance to most any combination of standard
    cables on loops to 1600 Ohms DC. Beyond that distance, signaling became a
    problem and other technologies were used.


    Don
     
  7. Thanks for this- I was trying to see if I could avoid using back to back 2-4
    wire hybrids
    anthony
     
  8. The application is not for a home phone- I am trying to place a fire
    telephone system line 5Km from the rack, client wants to use existing copper
    network, I am trying to use known technology for the link- hence the use of
    extenders- someone mentioned the BT extenders- I could not find referance to
    them on Google so I thought I would ask
    Any body got a schematic- or am I left with back to back hybrids?
    regards
    Anthony
     
  9. Joop

    Joop Guest

    If you only need a single remote telephone set you may want to try a
    simple cordless home phone kit. Leave the base station at the rack.
    Take the mobile set remote and connect the antennas to each end of the
    the wire. You may need some terminator resistors.
    You never know, it might just work and cost is low to try it out. I
    suggest not to use DECT but the cheap stuff that has a much lower
    frequency band it operates in (49MHz?)

    Joop
     
  10. Not realy practicable- the fire phones must be monitored, I don't want to do
    a complete product redesign so I am looking for basic phone technology
    Anthony
     
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