MODULATOR COMPENSATED FOR VARYING MODULATING SIGNAL LEVEL

• US 3,651,429 A
• Filed: 12/09/1970
• Issued: 03/21/1972
• Est. Priority Date: 12/09/1970
• Status: Expired due to Term

• Current Assignee: Clyde Leslie Ruthroff
• Original Assignee: Clyde Leslie Ruthroff
• Inventors: Ruthroff, Clyde Leslie
• Primary Examiner(s): Brody, Alfred L.
• Application Number:
  US05/096,346
• Time in Patent Office: 468 Days
• Field of Search: 332/16,18,19 325/46,145,147,187
• US Class Current: 332/119
• CPC Class Codes: H03C 3/40 using two signal paths the outputs of which have a predetermined phase difference and at least one output being amplitude-modulated

Abstract

A phase or frequency modulator of the quadrature or Armstrong type is modified such that the amplitude of the quadrature component will be reduced in proportion to any reduction in the power of the modulating signal so that the modulation index remains constant despite variation in the level of the modulating signal.

Claims

1. In combination with a frequency modulator of the type in which one portion of a carrier signal is mixed with a modulating signal and another portion is shifted in phase before combination with said mixed one portion to produce a frequency modulated sum, a plurality of intelligence signal channels some of which may periodically have low amplitudes, means for combining said channels into a composite signal to form said modulating signal, means for deriving an indication of the power in said composite signal, and means responsive to said indication for varying the relative amplitudes of said carrier portions whereby the index of modulation is maintained constant despite said periodic low levels.

2. In combination with a frequency modulator of the type in which one portion of a carrier signal is amplitude modulated by an intelligence signal and another portion is shifted in phase before combination with said amplitude modulated one portion to produce a frequency modulated sum having a modulation index, a source of said intelligence signal having a varying output level, means for deriving an indication of said output level, and means responsive to said indication for varying the amplitude of said other portion whereby said index is maintained constant despite said varying level.

3. The combination according to claim 2 wherein said indication comprises a current proportional to the root-mean-square value of said intelligence signal.

4. The combination according to claim 3 including means responsive to said current for regulating said other portion so that the amplitude of said other portion varies in proportion to said current and said root-mean-square value.

5. A frequency modulator for impressing an intelligence signal of varying level upon a carrier signal, means for dividing said carrier signal into two parts, means for varying the ratio of the amplitude level of said parts in response to the power in said intelligence signal, and means for successively combining said parts and said intelligence signal in a quadrature type frequency modulator to produce a modulated wave of relatively constant index of modulation despite said varying level intelligence signal.

6. The modulator according to claim 5 wherein one of said parts is shifted in phase by 90* to become the quadrature signal in said modulator and wherein the amplitude level of said one part is varied in response to the power in said intelligence signal.

7. A frequency modulator for impressing an intelligence signAl of varying level upon a carrier signal, including means for deriving an indication of the power in said intelligence signal, means for dividing said carrier signal into two parts, means for varying the amplitude level of one of said parts in response to said indication, and means for first combining the other part with said intelligence signal and then said amplitude varied one part with the product of said other part and said intelligence signal to produce a modulated wave of relatively constant index of modulation.