CES SDI-50 - 9.3 Signal Level Conversion

C.E.S. Model SDI-50 Manual, Circuit Description
noise oniy. The level of noise on the radio channel indicates
the presence or absence of an RF carrier. The noise level is
adjusted by R91 and sent to a network that gives a peak DC
reading of the amount of noise on the channel. This signal is
sent to a comparator (half of U18) that provides a logic level
signal to the microcomputer.
9.1.10
CTCSS Level Comparator
U17 is a comparator with adjustable threshold (set by R45) which
is used to convert the DC voltage from the radio decode circuit
to the proper logic level for the microcomputer.
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