US PATENT SUBCLASS 379 / FOR 120
.~.~.~ By modulated audio tone (379/98)

Current as of: June, 1999
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379 /   HD   TELEPHONIC COMMUNICATIONS

FOR 112  DF  TELEPHONE LINE OR SYSTEM COMBINED WITH DIVERSE ELECTRICAL SYSTEM OR SIGNALLING (E.G., COMPOSITE) (379/90) {8}
FOR 115  DF  .~ With transmission of a digital message signal over a telephone line (379/93) {4}
FOR 119  DF  .~.~ By voice frequency signal (e.g., tone code) (379/97) {2}
FOR 120.~.~.~ By modulated audio tone (379/98)

DEFINITION

Classification: 379/FOR.120

By modulated audio tone:

Foreign art collection wherein a pulse or digital data signal causes a variation in the frequency, phase or amplitude of an audible tone.