LANDLINE FACSIMILE SYSTEM

• US 3,591,711 A
• Filed: 05/26/1966
• Issued: 07/06/1971
• Est. Priority Date: 05/26/1966
• Status: Expired due to Term

• Current Assignee: Groat Paul H De
• Original Assignee: Groat Paul H De
• Inventors: GROAT PAUL H DE
• Application Number:
  US04/553,175
• Time in Patent Office: 1,867 Days
• US Class Current: 379/93.37
• CPC Class Codes: H04N 1/00095 Systems or arrangements for the transmission of the picture signal

Abstract

A skip frequency circuit for selectively excluding from the signal spectrum thereof any tonal frequency signals which fall within a predetermined forbidden band in the transmission network of a facsimile system. The forbidden bands would be defined by those control frequencies employed in the landline telephone transmission facilities over which the facsimile system is to operate. In response to the detection of signals within a forbidden zone, a skip or jump is automatically initiated, thus shifting the facsimile video signals to another level thereby avoiding the generation of signal frequencies within a predetermined forbidden frequency zone.

Claims

1. A facsimile system operable over a standard commercial telephone transmission facility comprising:

scanning means for generating electric video signals corresponding to the reflectivity along a predetermined scanning raster of a document to be transmitted, modulation means for generating predetermined tonal frequency signals within a predetermined signal spectrum in response to various levels of said video signal, skip frequency means responsive to a predeTermined condition in said video signal for preventing the generation of tonal frequency signals lying within a predetermined forbidden frequency band in said predetermined signal spectrum, said skip frequency means comprising threshold sensitive means for detecting signal voltage levels within a predetermined voltage range in said video signal, and clamp means responsive to signals emanating from said threshold sensitive means for generating a predetermined control signal, first coupling means for coupling said tonal signals from said modulation means to an input terminal of said telephone transmission facility, second coupling means for coupling said tonal signals from an output terminal of said telephone transmission facility to a receiver, demodulator means at said receiver responsive to said signals emanating from said second coupling means for generating said recording signals from said tonal signals, and marking means responsive to said recording signals emanating from said demodulator means for reproducing a copy of said document in response thereto.

2. A facsimile system operable over a standard commercial telephone transmission facility comprising:

scanning means for generating electric video signals corresponding to the reflectivity along a predetermined scanning raster of a document to be transmitted, modulation means for generating predetermined tonal frequency signals within a predetermined signal spectrum in response to various level of said video signal, skip frequency means responsive to a predetermined condition in said video signal for preventing the generation of tonal frequency signals lying within a predetermined forbidden frequency band in said predetermined signal spectrum, means for delaying the actuation of said skip frequency means until said predetermined condition in said video signal is detected for at least a predetermined time interval, first coupling means for coupling said tonal signals from said modulation means to an input terminal of said telephone transmission facility, second coupling means for coupling said tonal signals from an output terminal of said telephone transmission facility to a receiver, demodulator means at said receiver responsive to said signals emanating from said second coupling means for generating said recording signals from said tonal signals, and marking means responsive to said recording signals emanating from said demodulator means for reproducing a copy of said document in response thereto.

3. The facsimile system defined in claim 2 additionally including polarity sensitive shunt means for rendering said delay means ineffective during video signal excursions toward a predetermined signal level.

4. A facsimile system operable over a standard commercial telephone transmission facility comprising:

scanning means for generating electric video signals corresponding to the reflectivity along a predetermined scanning raster of a document to be transmitted, modulation means for generating predetermined tonal frequency signals within a predetermined signal spectrum in response to various levels of said video signals, said modulation means including a voltage control oscillator, skip frequency means responsive to a predetermined condition in said video signal for preventing the generation of tonal frequency signals lying within a predetermined forbidden frequency band in said predetermined signal spectrum, and skip frequency means including a Schmitt trigger circuit and diode means for coupling the output of said Schmitt trigger circuit to an input of said voltage control oscillator, first coupling means for coupling said tonal signals form said modulation means to an input terminal of said telephone transmission facility, second coupling means for coupling said tonal signals from an output terminal of said telephone transmission facility to a receiver, demodulator means at said receiver responsive to said signAls emanating from said second coupling means for generating said recording signals from said tonal signals, and marking means responsive to said recording signals emanating from said demodulator means for reproducing a copy of said document in response thereto.

5. The method of transmitting tonal facsimile signals over standard telephone lines having predetermined forbidden frequency ranges within a predetermined signal spectrum comprising the steps of:

generating analog video signals corresponding to the variations in the reflectivity along a predetermined scanning raster of a document to be transmitted, generating one of the plurality of discrete unique tonal frequency signals within said predetermined signal spectrum in response to the occurrence of each of a like plurality of signal levels in the analog video signal, monitoring the analog video signals to detect the occurrence of video signal voltage levels within a predetermined range, coupling the tonal frequency signals to the input of a telephone line, and excluding the transmission of predetermined tonal frequency signals falling within said predetermined forbidden frequency ranges within said predetermined spectrum from the tonal frequency signals coupled to the telephone line, said step of excluding the transmission of predetermined tonal signals including the step of delaying the excluding the transmission of said predetermined tonal signals until said video signal voltage levels within said predetermined range have reached a predetermined threshold level.

6. The method of transmitting tonal facsimile signals over standard telephone lines having predetermined forbidden frequency ranges within a predetermined signal spectrum comprising the steps of:

generating analog video signals corresponding to the variations in the reflectivity along a predetermined scanning raster of a document to be transmitted, generating one of a plurality of discrete unique tonal frequency signals within said predetermined signal spectrum in response to the occurrence of each of a like plurality of signal levels in the analog video signal, monitoring the analog video signals to detect the occurrence of video signal voltage levels within a predetermined range, coupling the tonal frequency signals to the input of a telephone line, and excluding the transmission of predetermined tonal signals falling within said predetermined forbidden frequency ranges within said predetermined signal spectrum from the tonal frequency signals coupled to said telephone line, said step of excluding the transmission of predetermined tonal signals including the step of generating a predetermined frequency signal above the forbidden frequency range in response to the detection of an analog signal level within said predetermined voltage range.