Test Transmitter

The Test Transmitter (A3020) is a combination of three circuits. Its purpose is to allow us to test the Subcutaneous Transmitter ( A3019 ) and to investigate SAW (surface acoustic wave) VCOs (voltage-controlled oscillators). The A3020 contains the complete A3019 circuit in its center section. The circuit is almost identical to that of the Subcutan

eous Transmitter ( A3013 ). The most significant changes are as follows. Replace reed switch with Hall Effect Switch. The old magnetic switch was easy to break and large, not to mention its being discontinued by the manufacturer. Magnet turns off all power to circuit except Hall Effect Switch. The transmitter is either ON or OFF. When it`s OFF, the only current drain is the Hall Effect Switch. When it is ON, it is transmitting. Two op-amps used for amplification and filtering instead of three. We reduce the DC gain of the main amplifier stage by adding a capacitor to its feeback loop. The capacitor sets the lower limit of the operating bandwidth at around 1 Hz. Power supply decoupling done so as to favor analog circuits. We use the battery and regulator directly for analog circuits, and supply current to the digital circuits and VCO through resistors that keep transmission noise off the analog supplies. The SAW VCO circuits continue the earlier work we did with our RF Tester ( A3014 ) and RF Combo ( A3016 ) circuits. In the new SAW circuits, we are able to vary the feedback track length in order to provoke oscillations, and we are able to short a stub track to ground in order to cause phase changes. Figure: The A3020A Circuit. The middle section provides the circuit drawn in S3020_1, the test transmitter. The right section, which we have cut off because it is independent, provides S3020_2, the SAW oscillator. The left...

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