Motorola R-2001A Service Manual page 194

19-1. General. The frequency Standard Module provides a stable 10 MHz source and the interface for an
external 10 MHz input. A block diagram of the Frequency Standard Module is shown in figure 19-1 with its
schematic shown in figure 19-2.
19-2. 10 MHz Oscillator and Control. The internal 10 MHz source is either a temperature compensated
crystal oscillator (TCXO) or an optional ovenized crystal oscillator (OVXO). A voltage regulator on the module
supplies the voltage to the oscillator and monitors the supply current. For the ovenized option, at power on the
oven draws high current. As the oven warms up the current decreases, reaching some low valve when the
operating temperature has been reached. A current detector illuminates the oven ready indicator when the
current has decreased to the stabilized valve. The indicator is continuously illuminated with the TCXO.
19-3. Internal/External Switchover. With no signal at the external 10MHz input jack, the internal oscillator
is gated to the SYNTH 10 MHz and the external 10 MHz OUT signal paths. When an external 10 MHz input is
applied the switchover circuitry detects its presence, removes the power from the internal oscillator, and gates
the external input to the SYNTH 10 MHz and external 10 MHz OUT signal paths. The oven ready indicator is
extinguished when the system is operating from an external standard.
10 MHz FREQUENCY STANDARD MODULE (A13)
SECTION 19
19-1