GE Medical Systems Corometrics 340, Service Manual, Page: 47 / 82

Revision A Model 340 Telemetry System 4-7
2006920-001
Theory of Operation: Telemetry Receiver Board Circuitry (No. 13856A)
Telemetry Receiver Board Circuitry (No. 13856A)
The RF Receiver
The RF receiver used by the Telemetry Receiver Board provides both the
encoded modulation from the transmitter, as well as a voltage output
that is proportional to the RF signal level received.
The signal level output from the RF receiver is connected to a pair of
comparators configured as a threshold detector and monostable. When
the received signal exceeds the comparator threshold, the first
comparator fires enabling the monostable. The output of the monostable
remains enabled as long as the signal level output from the RF receiver
exceeds the threshold of the first comparator, and for drop outs of less
then one-half second. The output of the monostable, in conjunction with
TTL inverters and transistor drivers, is used to light a set of
complementary LEDs. The LEDs are used on the front panel to indicate
a received signal condition, as well as to provide an overall enable to a set
of OR gates that control FET switches. The FET switches provide the
mode enables to the connected fetal monitor.