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ssnader
Joined: 06 Nov 2006
Posts: 1
Location: ---------
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 Posted:
Mon Nov 06, 2006 10:51 pm Post subject:
how does the frequency system work on telephone lines? |
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since no two tv or radio channel signals can be broadcasted on the same frequency without both intefering with one another, Im wondering how thousands of people are able to talk to one another on land line phones at the same time without their signals intefering. Wouldn't that require thousands of different frequencies for thousands of people. Obviously, there's a method Im not aware of and would appreciate some Info on.
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Retiredguy
Joined: 13 Nov 2006
Posts: 8
Location: Kent, OH
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Mon Nov 13, 2006 4:32 pm Post subject:
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Having been a cable splicer for the phone Co. for the past 35 years I think I can answer your Question. First of all, telephone cables are comprised of many twisted insulated copper pairs of wires which are bundled together in groups of 25 to 100 pairs each depending on the wire gauge of the conductor. Each pair of wires is for a single telephone circuit and go from a subscribers phone or phones to a switching location where they are directed to who ever one wishes to call. One side of the cable pair is grounded at the switching office which will dirrect some of the crosstalk (the condition which you describe) to ground. Now days almost all of the cables between switching offices are fiber optics and are transmitted by light to another location digitally and are converted back to analog just before it is put back on the copper conductors to another subscriber. Also take into account that voice frequency is only in the range of about 50 Hz to maybe about 5000 Hz if that much, which are some very long wavelengths. In the old days yes, some of what you describe did happen on very long transmission through all copper networks, where one might hear part of anothers conversation and also an echo accured from the capacitance generated by the twisted pair side to side which would generate a phase shift between the voltage and current of the signal. Hope this answered some of your questions.
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Retired Guy |
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neon
Joined: 25 Feb 2006
Posts: 590
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Fri Jun 08, 2007 9:29 am Post subject:
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VERY INTERESTING knowledge like this should not get lost THANKS
| Retiredguy wrote: | | Having been a cable splicer for the phone Co. for the past 35 years I think I can answer your Question. First of all, telephone cables are comprised of many twisted insulated copper pairs of wires which are bundled together in groups of 25 to 100 pairs each depending on the wire gauge of the conductor. Each pair of wires is for a single telephone circuit and go from a subscribers phone or phones to a switching location where they are directed to who ever one wishes to call. One side of the cable pair is grounded at the switching office which will dirrect some of the crosstalk (the condition which you describe) to ground. Now days almost all of the cables between switching offices are fiber optics and are transmitted by light to another location digitally and are converted back to analog just before it is put back on the copper conductors to another subscriber. Also take into account that voice frequency is only in the range of about 50 Hz to maybe about 5000 Hz if that much, which are some very long wavelengths. In the old days yes, some of what you describe did happen on very long transmission through all copper networks, where one might hear part of anothers conversation and also an echo accured from the capacitance generated by the twisted pair side to side which would generate a phase shift between the voltage and current of the signal. Hope this answered some of your questions. |
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