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Phase comparison is provided by U803, an ECL Phase-Frequency
Detector. The external frequency input at J801 is discriminated by
comparator U809 and coupled through ECL Line Receivers U805C and
U805D to one input of the phase detector. The other input is from the
frequency output selected by fast multiplexer U806, and is coupled
through ECL line receivers U805A and U805B. A bipolar analog output
from U804D indicating the relative phase of the two inputs is provided
to the system A/D, and is buffered by U804A and provided to the front
panel VPHASE output J803.
The 10 MHz system clock is divided by U807 and U808 to provide
frequency outputs of 5 MHz, and 100 kHz. These frequencies, along
with the 10 MHz source and the outputs from the programmable
counters (see sheet 3) are provided as inputs to U806, the fast
multiplexer. The multiplexer output is the Frequency Output used for
phase comparison, and is buffered through U810 to the front panel
BNC J802. The 5 MHz system clock is derived from the 10 MHz
source and buffered by U203E.
The 100 kHz calibration signal that is fed to the front end calibration
relay is derived from the OUT_FREQ1 counter output. The signal is
attenuated and filtered by R824, R816, and C808 and AC-coupled
through C807. R829 is a pull-down to satisfy the antenna error
detection circuitry.
Front Panel LED's / Switches (p. 10/14)
The front panel LED indicators are connected to +5 V through resistor
network N702, and are controlled by eight lines from latch U43 (Sheet
4). The eight switch lines are normally held low through resistor network
N701. A key press is detected by scanning the REM, NUM, and CURS
LED control lines and reading the switch input port. Diodes D709,
D710, and D711 prevent simultaneous key presses from shorting LED
lines together.
Unregulated Power Supplies (p. 11/14)
The power entry module configures the unit to line voltages of 100, 120,
220, or 240 VAC and provides fuse protection and an RF interference
filter. An 130 VAC Metal Oxide Varistor across the 120 VAC
transformer primary provides spike and surge protection for the unit,
and additionally protects against inadvertent connection to 220 or 240
VAC when configured for 100 or 120 VAC.
Full-wave rectification of the center-tapped secondary outputs of T1
provides unreg7 V and ±20 V. Schottky diodes D902 and D903
are used in the +7 volt supply to reduce rectifier losses. Diode bridge
D901 is used for the +20 and -20 volt supplies.
The unregulated supplies operate as long as the unit is connected to AC
power. This is to provide uninterrupted power to the time base
