Miniature transmitter and method for making same

• US 4,327,444 A
• Filed: 06/04/1979
• Issued: 04/27/1982
• Est. Priority Date: 06/04/1979
• Status: Expired due to Term

• Current Assignee: Clifford Electronics, Inc. (VOXX International Corporation)
• Original Assignee: TMX Systems Limited
• Inventors: Court, Patrick R. J.
• Primary Examiner(s): Chin, Tommy P.
• Application Number:
  US06/045,129
• Time in Patent Office: 1,058 Days
• Field of Search: 455/63, 455/89, 455/95, 455/100, 455/106, 455/114, 455/90, 455/128, 455/129, 455/121, 455/123, 455/125, 455/107, 455/300, 455/100, 334/5, 334/6, 334/45, 343/718, 343/868
• US Class Current: 455/100
• CPC Class Codes: H04B 1/04 Circuits

Abstract

There is disclosed a miniature hand-held radio-frequency transmitter. An operating frequency is determined by a lumped-circuit oscillator which feeds an antenna etched on the periphery of the circuit board. The antenna is tuned to a frequency which is slightly above the second harmonic of the operating frequency, it being the second harmonic which is radiated. By slightly mis-tuning the antenna, the effects of an enveloping hand are minimized. The clasping of the transmitter by a human hand results in the absorption of some of the radiated power, but hand-capacitance effects also shift the center frequency of the antenna characteristic toward the second harmonic of the operating frequency, thus increasing the radiated power. In this way the signaling range under free-space conditions is the same as that under operating conditions. The oscillator circuit can thus be adjusted for maximum power output under free-space conditions within the guidelines of F.C.C. Regulations, without the signaling range being appreciably reduced under operating conditions. The radiated frequency is not appreciably affected by hand capacitance effects because it is determined by a lumped-circuit oscillator.

Claims

1. A miniature hand-held radio-frequency transmitter comprising a housing;

a fixed-frequency transmitter circuit mounted within said housing;

battery means within said housing for powering said transmitter circuit; and

switch means on the exterior of said housing, when operated, for controlling said transmitter circuit to generate a predetermined frequency;

characterized by said transmitter circuit having a detuned antenna which is fed a signal which is integrally related, but not equal, to said predetermined frequency and which is tuned to a frequency which is slightly different from said signal such that the power radiated by the detuned antenna is at a level lower than the maximum power which would otherwise be radiated thereby, the clasping of said housing by a hand shifting the center frequency of the antenna characteristic toward the frequency of said signal such that absorption of radiated power by an enveloping hand is automatically compensated by hand-capacitance effects which shift the center frequency of the antenna characteristic toward the frequency of said signal so that the radiated power is approximately the same and equal to said lower level whether the transmitter operates in free space or is clasped by a hand.

2. A miniature hand-held radio-frequency transmitter in accordance with claim 1 wherein said transmitter circuit is mounted on a circuit board, and said antenna is etched on the periphery of said circuit board.

3. A miniature hand-held radio-frequency transmitter in accordance with claim 2 wherein the frequency of said signal and said predetermined frequency are integrally related by a factor of two.

4. A miniature hand-held radio-frequency transmitter in accordance with claim 3 wherein said transmitter circuit includes lumped-circuit components to the exclusion of a crystal.

5. A miniature hand-held radio-frequency transmitter in accordance with claim 4 wherein said antenna is detuned by at least 2 dB.

6. A miniature hand-held radio-frequency transmitter in accordance with claim 4 wherein said antenna is detuned by at least 3 dB.

7. A miniature hand-held radio-frequency transmitter in accordance with claim 1 wherein the frequency of said signal and said predetermined frequency are integrally related by a factor of two.

8. A miniature hand-held radio-frequency transmitter in accordance with claim 7 wherein said transmitter circuit includes lumped-circuit components to the exclusion of a crystal.

9. A miniature hand-held radio-frequency transmitter in accordance with claim 8 wherein said antenna is detuned by at least 2 dB.

10. A miniature hand-held radio-frequency transmitter in accordance with claim 8 wherein said antenna is detuned by at least 3 dB.

11. A miniature hand-held radio-frequency transmitter in accordance with claim 1 wherein said transmitter circuit includes lumped-circuit components to the exclusion of a crystal.

12. A miniature hand-held radio-frequency transmitter in accordance with claim 11 wherein said antenna is detuned by at least 2 dB.

13. A miniature hand-held radio-frequency transmitter in accordance with claim 11 wherein said antenna is detuned by at least 3 dB.

14. A miniature hand-held radio-frequency transmitter in accordance with claim 1 further including metal sheets on opposed sides of said housing for shielding the operative parts of said transmitter circuit but not said antenna.

15. A miniature hand-held radio-frequency transmitter in accordance with claim 1 wherein said antenna is detuned by at least 2 dB.

16. A miniature hand-held radio-frequency transmitter in accordance with claim 1 wherein said antenna is detuned by at least 3 dB.

17. A method of making a miniature hand-held radio-frequency transmitter comprising the steps of fabricating a fixed-frequency transmitter circuit and mounting it within a housing;

placing battery means within said housing for powering said transmitter circuit;

placing switch means on the exterior of said housing which, when operated, controls operation of said transmitter circuit; and

placing an antenna within said housing arranged to be fed a signal from said transmitter circuit;

characterized by the step of deliberately detuning said antenna so that it is tuned to a frequency which is slightly different from the frequency of the signal fed thereto, such that the power radiated by the detuned antenna is at a level lower than the maximum power which would otherwise be radiated thereby, the clasping of said housing by a hand shifting the center frequency of the antenna characteristic toward the frequency of the signal fed thereto such that absorption of radiated power by an enveloping hand is automatically compensated by hand-capacitance effects which shift the center frequency of the antenna characteristic toward the frequency of said fed signal so that the radiated power is approximately the same and equal to said lower level whether the transmitter operates in free space or is clasped by a hand.

18. A method of making a miniature hand-held radio-frequency transmitter in accordance with claim 17 wherein said transmitter circuit is fabricated on a circuit board and said antenna is formed by etching it on the periphery of said circuit board.

19. A method of making a miniature hand-held radio-frequency transmitter in accordance with claim 17 wherein said transmitter circuit is fabricated of lumped-circuit components to the exclusion of a crystal.

20. A method of making a miniature hand-held radio-frequency transmitter in accordance with claim 19 wherein said antenna is detuned by at least 2 dB.

21. A method of making a miniature hand-held radio-frequency transmitter in accordance with claim 19 wherein said antenna is detuned by at least 3 dB.

22. A method of making a miniature hand-held radio-frequency transmitter in accordance with claim 17 wherein said transmitter circuit generates a frequency which is integrally related, by a factor of two, to the frequency of the signal which is fed to said antenna.

23. A method of making a miniature hand-held radio-frequency transmitter in accordance with claim 22 wherein said transmitter circuit is fabricated of lumped-circuit components to the exclusion of a crystal.

24. A method of making a miniature hand-held radio-frequency transmitter in accordance with claim 23 wherein said antenna is detuned by at least 2 dB.

25. A method of making a miniature hand-held radio-frequency transmitter in accordance with claim 23 wherein said antenna is detuned by at least 3 dB.

26. A method of making a miniature hand-held radio-frequency transmitter in accordance with claim 17 wherein said transmitter circuit is fabricated of lumped-circuit components to the exclusion of a crystal.

27. A method for making a miniature hand-held radio-frequency transmitter in accordance with claim 17 further including the step of placing metal sheets on opposed sides of said housing for shielding the operative parts of said transmitter circuit but not said antenna.

28. A method of making a miniature hand-held radio-frequency transmitter in accordance with claim 17 wherein said antenna is detuned by at least 2 dB.

29. A method of making a miniature hand-held radio-frequency transmitter in accordance with claim 17 wherein said antenna is detuned by at least 3 dB.

30. A miniature hand-held radio-frequency transmitter comprising a housing;

a fixed-frequency transmitter circuit mounted within said housing;

battery means within said housing for powering said transmitter circuit;

switch means on the exterior of said housing, when operated, for controlling operation of said transmitter circuit; and

an antenna;

characterized by means for feeding to said antenna a signal derived from said transmitter circuit whose frequency is slightly different from the center frequency to which said antenna is tuned such that the power radiated by the detuned antenna is at a level lower than the maximum power which would otherwise be radiated thereby, the clasping of said housing by a hand shifting the center frequency of the antenna characteristic toward the frequency of said derived signal such that absorption of radiated power by an enveloping hand is automatically compensated by hand-capacitance effects which shift the center frequency of the antenna characteristic toward the frequency of said derived signal so that the radiated power is approximately the same and equal to said lower level whether the transmitter operates in free space or is clasped by a hand.

31. A miniature hand-held radio-frequency transmitter in accordance with claim 30 wherein said transmitter circuit is mounted on a circuit board, and said antenna is etched on the periphery of said circuit board.

32. A miniature hand-held radio-frequency transmitter in accordance with claim 31 wherein said transmitter circuit includes lumped-circuit components to the exclusion of a crystal.

33. A miniature hand-held radio-frequency transmitter in accordance with claim 32 wherein said antenna is detuned relative to the frequency of said derived signal by at least 2 dB.

34. A miniature hand-held radio-frequency transmitter in accordance with claim 32 wherein said antenna is detuned relative to the frequency of said derived signal by at least 3 dB.

35. A miniature hand-held radio-frequency transmitter in accordance with claim 30 wherein said transmitter circuit includes lumped-circuit components to the exclusion of a crystal.

36. A miniature hand-held radio-frequency transmitter in accordance with claim 30 wherein said antenna is detuned relative to the frequency of said derived signal by at least 2 dB.

37. A miniature hand-held radio-frequency transmitter in accordance with claim 30 wherein said antenna is detuned relative to the frequency of said derived signal by at least 3 dB.

38. A miniature hand-held radio-frequency transmitter in accordance with claim 37 further including metal sheets on opposed sides of said housing for shielding the operative parts of said transmitter circuit but not said antenna.

39. A miniature hand-held radio-frequency transmitter in accordance with claim 30 wherein said transmitter circuit is mounted on a circuit board, and said antenna is etched on the periphery of said circuit board, and further including metal sheets on opposed sides of said housing for shielding the operative parts of said transmitter circuit but not said antenna.

40. A miniature hand-held radio-frequency transmitter in accordance with claim 30 further including metal sheets on opposed sides of said housing for shielding the operative parts of said transmitter circuit but not said antenna.