EKG_FM_DEMODULATOR

Published:2009/7/3 2:23:00 Author:May | From:SeekIC

Devel oped as part of system using satellitefor relaying electrocardiograms and other medical data having bandwidth of 0.5 to 50 Hz. Audio signal serving as source of FM is applied to voltage-controlled 1-kHz oscillator having ±40% deviation for fullscale input. Corresponding audio signal at receiving location is fed to input of 565 phaselocked loop. Error voltage of loop, at pin 7, conitains data being sought as well as undesirable DC and AC components. DC component of error signal is removed by 741 differential amplifier following PLL. Following four-pole active RC low-pass filter eliminates high-frequency AC components and determines bandwidth of demodulator. Cutoff frequency is 100 Hz. Final 741 opamp scales and shifts output to reasonable value. Recorded output could not be distinguished from original EKG by doctors.-D. Nelson, Medical Data Relay via Oscar Satellite, Ham Radio, April 1977, p 67-73.



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