Wavetek 3000 Instruction Manual page 35

"K HZ'
SWITCHES
phase or frequency
in the signals
applied to the
phase detector inputs
produces an error
voltage at the phase
detector
output, which controls the
VCO . The system is stable only when
the phase and frequency error is zero,
so that the output frequency is
phase
locked to the 1 kHz reference signal .
3 .12 .3 PROGRAMMABLE DIVIDER
In order for the M31A to perform prop-
erly, the divider is designed to divide
the VCOfrequency by (10,000-Sk) where
S
k
is the number set on the "kHz" switches .
The divider counts the number of cycles
at its input and puts
out a pulse when
the count reaches 10,000 . The starting
count is the number shown on the
"kHz"
switches . For example, if the instrument
is set for 222 .500 MHz, this circuit would
divide by 9,500 (count from
500 to
10,000) . Therefore, the variable input
to the phase detector would be correct
(1 kHz) only if the VCO output were 9 0 500
MHz .
1 KHZ REF
S K = SETTING OF 'KHZ ° SWITCHES
Figure 3-17,
M31A - kHz Steps
3 .12 .4 UNLOCK INDICATOR
THEORY OF OPERATION
When the phase-locked loop is unlocked,
the LED on top of the module will light
and the front-panel ACCURACY lights will
flash .
A window detector monitors the voltage
level which is being fed from the phase
detector to the
VCO . If the
voltage
exceeds the normal operating range,
power is applied to the module light and
the flasher circuit on the Modulation
Board .
3-17