Wavetek 3000 - Level Control and AM; Phase-Locked Loops (PLL)

LEVEL CONTROL AND AM
The circuitry for controlling the
RF
output level is directly related to the
above leveling system because
changing
the DC level reference changes the
RF
output
level .
Of the 150 dB output range, 130 dB is
passive attenuation .
The remaining 20
dB is controlled by
changing the level
reference .

The VERNIER output control
has a 10 dB range .

The remaining 10 dB
is provided by switchingthe
level ref-
erence range .

This
range switch is pro-
vided so
that when AM is notrequired the
output
ampcan provide a carrier at the
highest possible
power .
Since the RF level can be voltage
con-
trolled, AM can be accomplished by ap-
plying the modulating signal to the
VERNIER level control . This causes the
reference
voltage to the Error Amp to
/ KHz
X7-AL
REF
change at the frequency of the modulat-
ing signal . The modulating signal is
from one of two internal oscillators
or
fromanexternal source .
3 .2 .2 Phase-Locked Loops
The basic
signal generatordiscussed in
Section
3 .2 .1 has a frequency range of
1 to 520
MHz, has an output which is
leveled and adjustable
andhas the abi-
lity to be
amplitude modulated . With
the above
circuitry, however, the ac-
curacy is only 3 MHz with
1 MHz resolu-
tion . To achieve the desired
1 kHzre-
solution
and .001% accuracy,the instru-
ment includes
four phase-locked loops .
Phase-locked loops
(PLL) #1, #2 and #4
are used to stabilize the Wide
Oscillator
and tune it in 1 kHz steps . See Figure
3-1 . The NarrowOscillator is included
in PLL
#3
which provides stabilization
and allows
FM operation .
Figure 3-2 . PLL #1
THEORY OF OPERATION
OUroar
3-3
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OUTPUT
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