This circuit is from an old Electroics Now. Its purpose is to protect the fax and modem lines of two computers of the time. Suppressors are types of the time.
We found this circuit in the Linear Applications Handbook of the National Semiconductor of 1994....
This tone-modulated transmitter was found in recent English documentation. The circuit operates in the 27...
This very low current circuit was found in the April 1995 issue of Electronics Now magazine. The...