Tech Stuff - DTMF Tones
The following table defines the tones used in DTMF (see ANSI T1.401-1988
Section 7.2):
Each tone is composed of a low-high pair of frequencies as defined in the
table:
| DTMF Char |
Low (Hz) |
high (Hz) |
| 1 |
697 |
1209 |
| 2 |
697 |
1336 |
| 3 |
697 |
1477 |
| 4 |
770 |
1209 |
| 5 |
770 |
1336 |
| 6 |
770 |
1477 |
| 7 |
852 |
1209 |
| 8 |
852 |
1336 |
| 9 |
852 |
1477 |
| * (star) |
941 |
1209 |
| 0 |
941 |
1336 |
| # (num) |
941 |
1477 |
| A |
697 |
1633 |
| B |
770 |
1633 |
| C |
852 |
1633 |
| D |
941 |
1633 |
DTMF Tone Power is given by the following table:
| Power |
dBm |
| Max. Power per tone |
+1.0 |
| Min. Power per Low freq. tone |
-10.5 |
| Min. power per High freq. tone |
-8.5 |
Notes: frequency limit is +- 1.5%, difference in power between the low
and high frequencies should not exceed 3dB and the power of the high frequency
tone should equal or exceed the low frequency tone.
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