Level modulator for facsimile transmitter

Claim 2

An asymmetrical system for effecting the level modulation of a frequency modulated facsimile carrier signal comprising a plurality of concatenated actiVe stages, each of said active stages coupled to its successor by a passive network, said network comprising; a parallel combination of a plurality of series connected resistors and a diode, each said resistor being a bi-directional device having the ratio of the voltage thereacross to the current therethrough substantially constant, and at least one capacitor connecting each junction between two consecutive resistors to a point of reference potential.

Claim 3

In a frequency modulated continuous wave facsimile transmitter, the improvement of a level modulator comprising: a. a low pass filter having an input for receiving an analog signal the magnitude of WhIch is indicative of facsimile information and having an output for providing level modulation signals, said filter comprising a plurality of concatenated stages each coupled to its successor by a passive asymmetrical filter network comprising a series combination of at least tWo resistors having at east one junction poInt therebetween, a diode connected in parallel with said series combination, and a capacitor connecting said junction point to a point of reference potential, said network thereby being adapted to give said filter asymmetrical response time properties primarily caused by the presence of said diode whereby said filter is adapted to respond differently for positive going signals than for negative going signals; b. a modulator having at least one input for receiving frequency modulated signals and signals for level modulating those frequency modulated signals, and having an output; c. first means coupling the output of said filter to a modulator input to provide level modulation signals to said modulator and for adjustably setting the maximum level of modulation; d. a voltage controlled oscillator having an input and an output, said oscillator input adapted to receive substantially the same signals as received by said filter, said oscillator output being coupled to a modulator input to provide frequency modulated signals thereto; and e. second means coupled to the output of said filter and to a modulator input for adjustably setting the minimum level of modulation.

Claim 4

In a frequency modulated continuous wave facsimile transmitter, the improvement of a level modulator comprising: a. a low pass filter having an input for receiving an analog signal the magnitude of WhIch is indicative of facsimile information and having an output for providing level modulation signals, said filter comprising a plurality of concatenated stages each coupled to its successor by a passive asymmetrical filter network comprising a series combination of at least tWo resistors having at east one junction poInt therebetween, a diode connected in parallel with said series combination, and a capacitor connecting said junction point to a point of reference potential, said network thereby being adapted to give said filter asymmetrical response time properties primarily caused by the presence of said diode whereby said filter is adapted to respond differently for positive going signals than for negative going signals; b. a modulator having at least one input for receiving frequency modulated signals and signals for level modulating those frequency modulated signals, and having an output; c. first means coupling the output of said filter to a modulator input to provide level modulation signals to said modulator and for adjustably setting the maximum level of modulation; d. a voltage controlled oscillator having an input and an output, said oscillator input adapted to receive substantially the same signals as received by said filter, said oscillator output being coupled to a modulator input to provide frequency modulated signals thereto; and e. second means coupled to the output of said filter and to a modulator input for adjustably setting the minimum level of modulation.

Claim 5

In a facsimile transmitter having a voltage controlled oscillator with a frequency controlling voltage input for providing frequency modulated facsimile signals as an output to a transmitter output amplifier, the improved method of level modulating in an analog manner the continuous wave frequency modulated signal to be transmitted and of effecting the transitions between levels comprising the steps of: increasing over a first time period the amplitude of said amplifier output in response to a voltage chAnge which increases the frequency of the voltage controlled oscillator output from a first value to a second value, said first value corresponding to white background information on the facsimile document to be transmitted, the magnitude of said amplitude increase being proportional to the magnitude of said voltage change; and decreasing, over a second time period greater than said first time period, the amplitude of said amplifier output in response to a voltage change which decreases the frequency of the voltage controlled oscillator output from said second value back to said first value, said second value corresponding to dark information on the facsimile document to be transmitted.

Claim 6

In a facsimile transmitter having a voltage controlled oscillator with a frequency controlling voltage input for providing frequency modulated facsimile signals as an output to a transmitter output amplifier, the improved method of level modulating in an analog manner the continuous wave frequency modulated signal to be transmitted and of effecting the transitions between levels comprising the steps of: increasing over a first time period the amplitude of said amplifier output in response to a voltage chAnge which increases the frequency of the voltage controlled oscillator output from a first value to a second value, said first value corresponding to white background information on the facsimile document to be transmitted, the magnitude of said amplitude increase being proportional to the magnitude of said voltage change; and decreasing, over a second time period greater than said first time period, the amplitude of said amplifier output in response to a voltage change which decreases the frequency of the voltage controlled oscillator output from said second value back to said first value, said second value corresponding to dark information on the facsimile document to be transmitted.