The Bell MF tone receiver module provides for the detection of the repertoire of 15 dual tones needs for various Bell MF signalling protocols. It is compliant with ITU-T Q.320, ITU-T Q.322, ITU-T Q.323B.
Basic Bell MF tone detection specs:
- Frequency tolerance +- 1.5% +-10Hz
- Signal level -14dBm to 0dBm
- Perform a "two and only two tones present" test.
- Twist <= 6dB accepted
- Receiver sensitive to signals above -22dBm per frequency
- Test for a minimum of 55ms if KP, or 30ms of other signals.
- Signals to be recognised if the two tones arrive within 8ms of each other.
- Invalid signals result in the return of the re-order tone.
Note: Above -3dBm the signal starts to clip. We can detect with a little clipping, but not up to 0dBm, which the above spec seems to require. There isn't a lot we can do about that. Is the spec. incorrectly worded about the dBm0 reference point, or have I misunderstood it?
