True, I am sending square waves. But at the receiver I have an opamp-based
filter/amplifier, so I got kind of confident about the square wave problem.

One extra information: it seems that on the great majority of times the
decoder misses the 2300 Hz separator tone...

Thanks again.


Pedro.






At 20:41 07/01/98 -0800, you wrote:
>Square waves are taboo on the phone lines.  The bandwidth is only about 300
>to 3000 Hz, and your square waves are making lots of harmonics than can be
>confused with a higher transmit frequency.  In addition, the higher
>harmonics, sampled at 8 kilohertz will alias down to the 300-3000 Hertz
>range and cause additional distortion of the signal you want to detect.
>Create sine waves, or low pass filter your square wave, and you will
>probably eliminate most of the problems you are having with various phone
>lines.