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Telecommunications

Wide-bandwidth-ultra-high-stability-FM-telemetry-transmitter

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Details

Inventors: Dinsmore, Mark T.;
Assignee: Transkinetic Systems, Inc. (Canton, MA)
Primary Examiner: Ng; Jin F.
Assistant Examiner:
Attorney, Agent or Firm: Weingarten, Schurgin, Gagnebin & Hayes

An FM transmitter especially for physiological signal telemetry includes a transistor oscillator having a collector-to-base capacitance that is part of its tuned circuit. Means are disclosed for controllably varying the collector-to-base capacitance only in response to impressed physiological or other signals to provide FM modulated signals for aerial transmission to any suitable receiver. Means including cooperative constant emitter current and constant collector voltage DC biasing circuits are disclosed for eliminating undesirable, changing temperature induced frequency variations. Means are further disclosed for neutralizing undesirable antenna loading induced frequency variations. The system is capable of accepting multiplexed inputs.

DETAILED DESCRIPTION The wide bandwidth high stability FM transmitter of the present invention provides highly reliable and repeatable signal telemetry that is free from undesirable thermal and loading effects while utilizing a minimum number of components that makes it compact and lightweight enough for physiological telemetry.
The FM transmitter of the present invention includes a variable frequency oscillator having a wide bandwidth tuneable circuit, contemplates means coupled to the variable frequency oscillator for completely stabilizing it against changing temperature induced frequency variations, and further contemplates means coupled to the oscillator for neutralizing loading induced frequency variations.
The FM transmitter of the present invention includes a transistor oscillator and a wide bandwidth LC tuned circuit in a Colpitts configuration.
A combination negative feedback circuit for maintaining a constant biasing transistor emitter current and a voltage regulator for maintaining a constant D.
C.
bias collector voltage are provided for completely stabilizing the transistor oscillator against changing temperature induced frequency variations.
A clamping and modulation circuit including a schottky diode across a portion of the LC tuned circuit is provided in one embodiment for maintaining radio frequency oscillation within the linear region of the transistor oscillator.
The temperature stabilized variable frequency transistor oscillator and wide bandwidth LC tuned circuit of the present invention are coupled to an output stage having a power amplifier and an antenna, and in one embodiment a phase inverting feedback transformer buffer having a manually adjustable capacitor is provided between the oscillator and output stage for neutralizing loading induced frequency variations.
In another embodiment, a two stage buffer and amplifier is provided therebetween with each stage having matched transistors and a self neutralizing push/pull transformer arrangement.
Radio frequency shielding is provided at least around the variable frequency oscillator in both embodiments for further neutralizing loading effects

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