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CIRCUIT DESCRIPTION
1.25 MHz
OUTPUTS
TM
OCXO1
OCXO2
When there is no output from the drawer, the RF
Output LED changes from green to flashing red indi-
cating failure.
When there is a difference of more than 10 Hz
between the two 10 MHz oscillators, the Delta F LED
changes from green to flashing red (failure).
The Delta F alarm circuit has built in hysteresis
and will not return to green until there is less than 5
Hz difference between the 10 MHz oscillators.
When both supplies are present, the AC LED is
green (active), and the DC LED is yellow (standby).
If the AC supply fails, the AC LED changes to flash-
ing red (failure) and the DC LED changes to green
(active) indicating that it is now powering the OCXO
drawer. If the external DC supply fails, the DC LED
changes from yellow (standby) to flashing red (fail-
ure).
All of these alarms are tied to relays that can be
set to open or close contacts upon alarms. The relay
contacts are connected to the 18-pin connector at the
rear of the drawer. These relay contacts are capable of
handling 1A DC current.
6.3.2 OCXOS, BUFFERS , DIVIDER AND LINE
DRIVER
The OCXOs produce a signal level greater than
1V RMS. Q901 and Q902 serve as buffers and square
up the signal from 0 to 5V (see Figure 6-5). Selection
October 1999
Part No. 001-2009-201
10 MHz
OUT
IN
OUTPUT
AC
DC
DELTA F
Figure 6-6 OCXO DRAWER FRONT/REAR PANELS
BACK PANEL
DC BACKUP
INTERRUPT
FRONT PANEL
of the oscillators as described in Section 6.3.1 is
accomplished by the logic gates U901-U904. The 10
MHz signal is then applied to the counter chip U905.
U905 is used to divide the 10 MHz signal by eight to
create 1.25 MHz.
The dual line driver chip U906 is used to drive
the 8-Way 1.25 MHz outputs and the 10 MHz output.
The signal is filtered to remove harmonics. The 1.25
MHz outputs have approximately 0 dBm of power into
50 ohms. The 10 MHz output delivers about 10 dBm
into 50 ohms.
6.3.3 OCXO SWITCHING (U901A-D, U902A-D,
U903D, U904A/D)
Refer to the OCXO switching circuitry in Figure
6-7. The circuit is broken down into three levels
where various tasks are performed. The bottom sec-
tion is for remote control input and selecting which
OCXO LED should indicate standby. U902A, pins 1-
2 (OSC 1 - OSC 2) come from the OCXO pulse detec-
tor circuits. A logic high on U902A, pin 1 (OSC 1)
indicates that OCXO 1 has output. Likewise, a logic
high on U902A, pin 2 (OSC 2) indicates that OCXO 2
has output.
NOTE: U902C, pin 8 (S) cannot be high unless both
OCXO pulse detectors indicate output. Therefore, no
remote switching of OCXOs is allowed unless both
OCXOs are running.
6-14
ALLOW 30 MINUTES WARM UP
FOR PROPER STABILIZATION
1 2 3 4
5 6 7 8 9 10 11 12 1314
15
16
1718
OCXO 1
OCXO 2
INTERRUPT
INTERRUPT
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