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FM demodulator

  • US 4,675,882 A
  • Filed: 09/10/1985
  • Issued: 06/23/1987
  • Est. Priority Date: 09/10/1985
  • Status: Expired due to Term
First Claim
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1. A method of digitally demodulating a received angle-modulated signal, said method comprising the steps of:

  • (a) inputting digitized quadrature samples of a signal centered approximately at zero frequency, said samples indicating a composite signal vector;

    (b) scaling said samples to a desired magnitude within a predetermined range;

    (c) calculating the nearest octant within which the scaled composite signal vector lies, said nearest octant comprising a coarse phase range value;

    (d) rotationally scaling the scaled composite signal vector to lie within a range between -π

    /4 to +π

    /4 radians;

    (e) calculating a second value equal to the tangent of the phase of the rotationally scaled signal vector;

    (f) calculating a third value equal to the phase angle of said signal vector by deriving the arctangent of said second value, said third value comprising a fine phase angle value;

    (g) summing the fine phase angle and coarse phase angle values to produce a composite phase angle sample equivalent to the phase angle of the input signal vector;

    (h) filtering said composite of phase angle samples to produce a sequence of demodulated message samples; and

    (i) outputting said demodulated message samples to an output register.

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