Transtelephonic electrocardiogram and voice signal transmitter-receiver system

A transmitter-receiver communication system is developed to provide simultaneous voice and electrocardiogram (ECG) transmission capability via the public switched telephone network. The basic voice frequency passband of a telephone circuit is approximately 0-4000 Hz, of which the voice actually occupies roughly 200-3400 Hz. For dual-channel signaling (voice and ECG) the voice signal is bandlimited to about 2500 Hz (still providing intelligible speech quality) and is mixed with an ECG signal transported to a 3000-Hz center frequency. The ECG signal is passed through a 250-Hz low-pass filter and is amplitude-modulated on a 3-kHz carrier frequency. On the receiving side these two signal channels are separated, and the ECG signal is demodulated to the baseband using a phase-locked-loop technique. The ECG signal is displayed on a monitor. The hard copy of the ECG signal can also be obtained using a strip chart recorder.<>