> I'll do my comments in line and hope I don't offend. > > Rich Adamson wrote: > >>First off, thank you *very* much for this unbelievably informative post! > >>I've > >>got it saved away now along with Kris Boutilier's adjusting rxgain/txgain > >>post. > >> > >>On Wednesday 24 August 2005 17:14, Bruce Ferrell wrote: > >> > >>>At the point where the phone line get's to your demarc the is supposed > >>>to ba a -2 to 3db reference point, sometimes called a -2 or -3 test > >>>level point (TLP). So that milliwatt tone at that point should read in > >>>the range of -2 to -3 dbm. > > > > > > If I read the above words exactly as written, the above is not true. Maybe > > there was a different intent that I'm missing, or, maybe words left out? > > I'm a lousy typist :) > > > I'm reading the words to say "if I put a transmission test set on the > > cable pair just before the pair leaves the central office, the reading > > should be in the -2 to -3 dbm range." If that is what you meant, then > > its incorrect. Even the old analog step-by-step switch specs called > > for no more then .5db loss from the milliwatt generator to the cable > > pair (CO distribution frame). > > > If you mean placing a transmission test set at the customer's demarc (at > > the customer's site), the -2 to -3 db is still incorrect for "analog" > > pstn circuits. That level _will be_ the 0db generator tone minus the cable > > loss from the CO to the customer's demarc. That cable loss is 100% > > predictable if you know the length and gauge of the copper wires between > > the central office and the customer's site. (That "is" exactly how the > > engineering spec is set for the less technical telephone installers > > to measure after installing a new pstn facility to a customer site.) > > at the last point leaving the CO, the tone level should be a nominal > 0dbm. By the time it get's to the customer demarc, -2 to -3 dbm. The > loops are "suppposed" to be engineered that way. On a brand spanky new > loop, yes 100% predictable. Over time, all sorts of oddities > (corrosion, half taps, loading coils, and just general funkieness) are > introduced in the real world.
The -2 to -3 db is not correct for analog circuits. Copper wires have a loss that is directly related to the length of the cable. (I don't have the chart right here, but a 7,000 foot cable pair will have lets say 6db of loss and a 3,000 foot pair will be a 3db loss. You can't engineer something into a copper pair to compensate for that loss.) The only thing that I can think of that you might be talking about is using an old analog carrier system on a copper pair. If that's what you're thinking, then yes -2 to -3 db is very reasonable. _______________________________________________ --Bandwidth and Colocation sponsored by Easynews.com -- Asterisk-Users mailing list Asterisk-Users@lists.digium.com http://lists.digium.com/mailman/listinfo/asterisk-users To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users