euatdt@euas11g.ericsson.se (Torsten Dahlkvist) (08/10/89)
O.K. so now we've been given the frequencies for DTMF dialling. What no-one has mentioned is the fact that the levels are crucial too. The one group (the higher or the lower, I can't remember) is a couple of dB's louder. This (as far as I can recall) is the same for Bell (U.S.) and CCITT (Europe). However, the nominal levels for the signals are different in Bell and CCITT countries. Bell, I think, is louder. Somebody out there to fill me in? The figures were on the order of -7/-9 dB for Bell and -11/-13 dB for CCITT, but my memory is very vague on the exact values. Of course, a variation of a few dB's doesn't matter much and a Bell phone usually works just fine in CCITT country (the reverse would probably be true in most cases except very long lines). Oh, by the way, the "dB" levels are of course weighted against the old traditional "1 mW into 600 Ohms" standard, giving a reference voltage of 0.7746 V. Does anybody know why the 600 Ohm standard line impedance has been replaced by "900 Ohm // 30 nF" for modern phones? /Torsten Torsten Dahlkvist ! "I am not now, nor have I ever ELLEMTEL Telecommunication Laboratories ! been, intimately related to P.O. Box 1505, S-125 25 ALVSJO, SWEDEN ! Dweezil Zappa!" Tel: +46 8 727 3788 ! - "Wierd" Al Yankowitz