At 11:14 AM 8/3/01 -0500, Jim wrote:
>    "567's data sheet they present the DTMF
>      decoding solution without this preamplifier."
>
>Yeah yeah yeah ... try using that bare-boned approach
>in the *real world* where the tone levels from each of  the
>two TT freq groups aren't *quite* the same level ... as can
>be seen in the amatuer radio world where TT levels (on TT
>mics) varies from rig to rig ...

The data sheet circuit tells you that the 567 can do this job, under ideal
conditions.
In real life, you have to deal with a huge range of amplitude (-9 to -40dBm
IIRC), several dB of twist in either direction, and noise.

The 567 is ok up to a point, but it doesn't work miracles.
Stick a filter in front, and you'll be much happier.


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