Why is Dry Loop cheaper?

Discussion in 'General Science & Technology' started by AcrossSkylight, Jan 29, 2013.

  1. AcrossSkylight Registered Member

    Messages:
    13
    Please I ask that only those that wish to participate positively in this discussion do so.
    There have been a few when I have asked a question their response made it seem like I am being a bother.
    Just know that I’m am vision impaired asking questions is a normal approach among those like me who needs to understand
    visual observations.
    If anyone asks of me a subject that I know I would be willing to answer in a letter. I’m accustomed to writing long answers on posts. I just need to improve in this field. I’m hoping this forum can be a good place to start in my research.

    Now I have these few questions. I read online to try to figure out what this “Dry Loop is? Sort of I understand sort of I don’t. It seems that dry loop is the Telephone Line separate from the Internet line. We had gotten Magic Jack. So now I ask this, does Dry Loop mean the phone line is separate from DSL? And now I ask why should this be any cheaper doing it this way?

    Now can anyone please answer about the Dry Loop?
     
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  3. Read-Only Valued Senior Member

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    10,296
    As an old phone guy, I can help you with this one.

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    First off, an ordinary phone line has some specialized equipment attached to it at regular intervals between your home (or office) and the telephone company Central Office that serves you - they are called "load coils." Their purpose is to correct for the poor frequency response of plain, twisted copper wire pairs. That frequency response problem results in the higher voice frequency being "rolled off" (attenuated) and would make your voice sound unnatural at the other end of the line. So the load coils add electrical capacitance ( just ordinary capacitors) to make up for the inductance introduced into the line by the wires running alongside each other.

    Then, to make up for that attenuation (lowering of the speech volume), amplifiers are installed in the telephone Central Office.

    A "dry loop" is needed to handle the higher frequencies and levels used in DSL and other data services and this is accomplished by removing ALL that extra equipment from the line, along with removing the "battery" (voltage) that provides dial-tone.

    With that said, practically all modern DSL service is a hybrid that allows for the DSL signal and ordinary telephone service to work simultaneously over the same pair of wires.

    The reason for any difference in price is due to the tarrifs (charged or allowed) by your state regulatory agency - they go by different names like Public Service Commission or Public Utilities Commission or something similar. And believe me, those tarrifs (rates) vary widely between different states.
     
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  5. AcrossSkylight Registered Member

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    Thanks for helping me with the phone issue. I kind of understand and sort of not. Some of these terms like load coils I’ve never heard in my life due to phone lines.

    Common words like dial tone, beeps, call waiting, redial and so on. That anyone should know. Now you are uncovering a whole new level of phones and telephone lines. As if like on a computer to look at the outside of the tower box and to open it up. Surely a difference from the inside to the outside like that of our own make up of our physical body.

    I’ll need to learn more about these load coils and other stuff. But I can’t devour all this in one day. I am a step by step day by day to grasp a bit here and a bit there.

    I have not repaired any electronics or repair inside the tower of a computer. However we all have to start from somewhere. Pieces on the table pick them up and study. This is just the stuff an operator would never share with you including state by state cost.

    I don’t wish to put phones out of service. But so far Magic Jack is working. We paid seventy dollar at Wal Mart. Her brother explained how to set it up. But then came the dry loop a part which I did not understand.

    Here is another thing I will share. AT and T is not a very good phone company in my opinion that in fact they set us up. They tell you it is certain amount each month to make it look like you got the best deal. But they require replacing for a new modem. Then they will charge for that and for the installation. Wow is that being sneaky.

    Well in that case we are looking for a new Internet Service provider after getting the MJ phone hookup. I don’t know who the best ISP is. But it is certainly not AT and T. We got to try to catch one of the promotions from one of these places.

    Have any of you ever heard of QualGuard? Several years ago a friend of mind got us on Qualguard. We only paid a one time fee of ten dollars. But then this was also dial up computers. Not DSL or cable. For one whom had cable got 20 dollars off but suddenly QG disappeared. Everyone said where did they go? I paid my fee and now they are gone. They were good while they lasted. Anyone ever had or heard QualGuard?
     
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  7. leopold Valued Senior Member

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    17,455
    loading coils are used to allow maximum energy transfer, they are impedance matching devices.
     
  8. AcrossSkylight Registered Member

    Messages:
    13
    Now about these loading coils where are they located? Are these located at the phone company? Outside or inside the house where the wires connect? Or is it located inside the phone itself?
     
  9. Read-Only Valued Senior Member

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    10,296
    You must have missed something in my original response to you.

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    I clearly said that the load coils were placed at specific intervals between your location and the Central Office that serves your phone. They are mounted on the utility poles.

    And no, Leo, they are not impedance matching devices. To be technical, they are nothing more than high-pass filters. Their purpose is to reshape the slope of the voice band back to a much flatter profile. The natural inductance of twisted pairs attenuates the higher frequency and the load coils (actually, a network of capacitors) attenuates the lower frequencies - the final result is a much more normal-sounding voice signal.
     
  10. leopold Valued Senior Member

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    17,455
  11. Read-Only Valued Senior Member

    Messages:
    10,296
    Even though my memory had failed me I stated the capacitance and inductance backwards (drat - the fact that they are 'coils' should have alerted me), the rest of what I said still stands. In telephony, the impedance matching is ALWAYS done by a device called a NBO (network build-out).

    And from the very link you provided, carefully note this, especially the first paragraph as it says the exact same thing I did:

    " Voice circuits
    A common application of loading coils is to improve the voice-frequency amplitude response characteristics of the twisted balanced pairs in a telephone cable. Because twisted pair is a balanced format, half the loading coil must be inserted in each leg of the pair to maintain the balance. It is common for both these windings to be formed on the same core. This increases the flux linkages, without which the number of turns on the coil would need to be increased.
    Loading coils inserted periodically in series with a pair of wires reduce the attenuation at the higher voice frequencies up to the cutoff frequency of the low-pass filter formed by the inductance of the coils (plus the distributed inductance of the wires) and the distributed capacitance between the wires. Above the cutoff frequency, attenuation increases rapidly. The shorter the interval between the coils, the higher the cut-off frequency.
    It should be emphasised that the cutoff effect is an artifact of using lumped inductors. With loading methods using continuous distributed inductance there is no cutoff.
    Without loading coils, the line response is dominated by the resistance and capacitance of the line with the attenuation gently increasing with frequency. With loading coils of exactly the right inductance, neither capacitance nor inductance dominate: the response is flat, waveforms are undistorted and the characteristic impedance is resistive up to the cutoff frequency. The coincidental formation of an audio frequency filter is also beneficial in that noise is reduced.


    [edit]DSL
    When loading coils are in place, signal attenuation remains low for signals within the passband of the transmission line but increases rapidly for frequencies above the audio cutoff frequency. Thus, if the pair is subsequently reused to support applications that require higher frequencies (such as analog or digital carrier systems or DSL), any loading coils that were present on the line must be removed or replaced with one which is transparent to DSL. Using coils with parallel capacitors will form a filter with the topology of an m-derived filter and a band of frequencies above the cut-off will also be passed.
    If they are not removed, as when the subscriber is an extended distance (e.g. over 4 miles) from the Central Office, DSL can not be supported. This sometimes happens in dense, growing areas (subject to frequent national numbering scheme repartitioning) such as Southern California in the late 1990s and early 21st century."
     
  12. billvon Valued Senior Member

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    12,723
    You're saying the same things. Impedance across frequency is the problem.
     
  13. leopold Valued Senior Member

    Messages:
    17,455
    i know, i just wanted to clarify things a little.
     
  14. Read-Only Valued Senior Member

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    10,296
    No , that's certainly not the same thing. I've been trying to explain to you that it's a filter and the purpose of a filter is *not* to match impedances. Impedance matching devices would only be used when the impedance of the transmission medium changed. For example, if the wire gauge changed from 22 to 24.
     
  15. leopold Valued Senior Member

    Messages:
    17,455
    Loading coils have one purpose in life, series inductance cancels shunt capacitance. That means that add a loading coil in a long telephone line and the loss that would normally comes with a long line is reduced.
    http://oldphoneguy.net/loading_coils.htm
    the above says it will maximize energy transfer.
    to do that the coil impedance must "cancel" the line capacitance.
    which implies an impedance matching device.
     
  16. Read-Only Valued Senior Member

    Messages:
    10,296
    That guy's education is obviously incomplete. In fact, he doesn't even provide the FULL name of the applied load coils - the most common one being 22H88. The first two digits represent the gauge of wire - and that's an *essential* factor in the design of the appropriate H-type loading.
    In addition, he seems to think that somehow (magically, I suppose!) the power level is preserved or actually INCREASED by passing it through the load coils - while in fact it's actually REDUCED!
     
  17. billvon Valued Senior Member

    Messages:
    12,723
    That's resistance. If we were just talking resistance you wouldn't need any sort of compensation. Impedance is the AC equivalent of the DC phenomenon called resistance, and consists of both resistance and reactance.

    This is an important distinction for several reasons. One is that impedance is only valid for a given frequency. For example, looking into a circuit you might see a resistance of 200 ohms DC (using your handy multimeter.) However, at 20Hz the impedance might be 200+j0 and at 20KHz the impedance might be 10-j50 due to stray capacitance in the circuit. In this case, if you were to drive it with a very stiff source (a source with almost zero source resistance) there would be almost no distortion in the signal. However, if you drove it with a source that had a source resistance of 10 ohms, then you'd see almost no distortion in the signal at 20Hz but you'd lose fully half the signal at 20KHz.

    To compensate for that you could 1) lower the source impedance, 2) add reactance to compensate for the capacitance to "smooth out" the impedance over frequency or 3) put in a high pass filter. In many cases 2) and 3) use exactly the same device (an inductor) and do exactly the same thing.
     
  18. leopold Valued Senior Member

    Messages:
    17,455
    wire gauge determines the resistance of the length of wire.
    inductive reactance (impedance, there are 2 kinds capacitive and inductive) is determined by the physical size of the coil, number of turns, and the core material.
    there are 2 ways wire size plays a role.
    1. a smaller diameter wire will allow a greater number of turns in a given space.
    2. at resonance the resistance seen by the input will be the resistance of the wire.
    a small diameter wire will give a greater bandwidth because of the increased resistance.
     

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