tholome@portia.stanford.edu (Eric THOLOME) (01/08/91)
Thanks to those who answered my last question. Unfortunately, I confused the two modes !!! I am looking for the frequencies used in tone mode phones. I know each key generates two frequencies more or less based on C D and E music notes, but I would like something a little bit more precise. Thanks again !!! Eric THOLOME holome@isl.stanford.edu Stanford University
tnixon@uunet.uu.net (Toby Nixon) (01/09/91)
DTMF tones are defined in CCITT Recommendation Q.23. The matrix looks
like this:
Hz 1209 1336 1477 1633
697 1 2 3 A
770 4 5 6 B
852 7 8 9 C
941 * 0 # D
The A/B/C/D tones are used in some feature phones on PBXes, and are
also available in some modems (including most from Hayes).
The transmitted frequency must be within +/- 1.8% of the nominal
frequency. Total distortion products (harmonics, intermodulation)
must be at least 20dB below the fundamental frequencies. The
transmitted level of the tones is not specified by the CCITT, and left
up to national requirements (I believe FCC Part 68 includes
restrictions, and EIA-496-A also has specs in this area).
See Recommendations Q.23 and Q.24 for more details.
Toby Nixon, Principal Engineer | Voice +1-404-449-8791 Telex 151243420
Hayes Microcomputer Products Inc. | Fax +1-404-447-0178 CIS 70271,404
P.O. Box 105203 | UUCP uunet!hayes!tnixon AT&T !tnixon
Atlanta, Georgia 30348 USA | Internet hayes!tnixon@uunet.uu.net