Frederick Electronics Corporation

H.f. Communications Corporation

J Howard Leveque

A linked compressor-expander (LINCOMPEX) circuit for use in telecommunications is implemented digitally. A speech compressor circuit in a modulator and a speech expander circuit in a demodulator controllably attenuate given syllables of a speech signal by values determined in response to binary input signals which collectively represent the amplitude of a given symbol of the speech signal. A control tone signal is generated by the modulator, and the demodulator is responsive to the control tone signal for operating the voltage attenuator circuit of the digital expander to thereby reconstruct the speech signal. Calibrate circuitry is provided for periodically detecting a test frequency of the control tone generator during a brief period prior to transmission of syllables of the speech signal. Also included is a data multiplexing circuit for transmitting and receiving data between speech syllables to optimize transmitter loading.

Method and apparatus for digitally implementing a linked

A phase locked loop signal generator is especially adapted for synthesizing a selectable frequency signal for exciting an HF radio frequency transmitter to transmit over the seven marine telegraph bands. The signal generator includes an oscillator for providing a highly stable frequency standard. Another signal generator is responsive to the frequency standard and to frequency selector signals input by the operator for generating an exciter signal which is coupled to the transmitter for effecting the RF transmission within a predetermined frequency range. The exciter signal generator includes: a reference dividing circuit programmable in response to the frequency selector signals for providing a reference frequency signal having a frequency which is a fractional part of that of the frequency standard; a phase locked loop circuit having a frequency divider in the feedback loop which is responsive to the reference frequency signal for producing an intermediate signal having a frequency which is a multiple of that of the reference frequency signal; and an output divider circuit is coupled to the phase locked loop circuit and is responsive to the frequency selector signal for generating the exciter signal to be at a frequency which is a fractional value of that of the intermediate signal. By varying the frequency selector signal, over 5000 transmitting frequencies are available using a conventional harmonic-related transmitter.

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Harper's Ferry, WV, United States of America

J Howard Leveque