HP 3312A - Modulation Operation Details; Amplitude Modulation Description; FM, Sweep, and Burst Operations

Section IV
3312 AB -- 4034
Figure 4-5. Signal Generator.
4-36. Amplitude Modulation. The AM modulator (Figure
7-4)
is
a
balanced
modulator
which
mixes
the
carrier
signal
from
the
main
generator
with
the
modulation
signal
from
the
modulation
generator.
The
carrier
frequency
is
applied
to
pin
7
of
U404
and
the
modulation
signal
is
input
to
pin
4.
Modulation
amplitude
control
resistor
R612
attenuates
the
modulation
signal
to
control
the
envelope
of
the
output
signal.
4.37, Frequency Modulation and Sweep. During FM and
sweep
operation
the
output
of
the
modulation
generator
is
applied
directly
to
the
Tuning
Amplifier
of
the
main
generator.
In
FM
operation
(Figure
4-6),
R612
controls
the
percent
of
deviation
in
frequency
of
the
carrier
waveform.
The
change
in
frequency
is
limited
to
+5%
of
the
carrier
frequency
by
current
limiting
resistor
AIR426.
All
three
functions
of
the
modulation
generator
are
available
for
modulating
the
main
generator
output
frequency.
4-38.
When
the
SWP
pushbutton
is
pressed,
resistors
R303
and
R308
are
selected.
If
R601
is
in
the
CAL
position,
the
output
of
U301
is
a
90:10
ramp
(Figure
4-7).
As
R601
is
rotated
clockwise,
t,
increases
and
flyback
time
is
increased.
4-39,
The
0
Hz
position
of
the
RANGE
Hz
knob
allows
pin
5
of
U303
(Figure
7-5)
to
go
high
producing
a
low
at
pin
6
of
U303
and
at
the
emitter
of
Q302.
Q302
begins
to
conduct,
turning
Q301
on
and
forming
a
loop
with
U302,
Q302,
Q301
and
U301.
In
SWP
the
square
wave
is
held
at
its
high
level
and
the
triangle
wave
ramps
to
-
10
V
then
REO! R304
Model 3312A
-8312 - 8-4037 -9Y
Figure 4-7. Sweep Operation.
stops. Start frequency, for the sweep of the main generator
output, can then be selected with R162. R162 affects the
frequency of the main generator by determining the
negative voltage level at which the ramp starts. Taking the
RANGE
Hz
knob
out
of
the
0
Hz
position
starts
the
modulation generator running and, as the ramp voltage
approaches zero volts, the output frequency of the main
generator approaches the frequency of the dial setting.
4-40. Burst. At any setting other than FREE RUN, the
tone burst gate is operable. The start/stop phase of the tone .
burst is determined by R615 (Figure 4-8) and the transistor
array U403. The signal always stops in the same phase as it
started.
4-4]. When TRIGGER PHASE is in FREE RUN the line
from the Burst Control is open and U402A pin 2 is pulled
low by the negative supply causing a high at the output of
U402A. As a result Q402 and U403(c) turn on and U403(a)
and (b) turn off. With U403(a) off, CR408 is reverse biased
and no charge is drawn off the integrating capacitor
allowing the main generator to free run.
4-42. In TRIGGER PHASE a low from the burst control
appears on U402A pin 2 forcing the output of U402A high
and starting the burst. When the burst control line goes high
again followed by a positive transition of the square wave
{at U402A pin 1) the output of U402A goes low. Q402
now turns off allowing TRIGGER PHASE POT, R615, to
3312 ~B-4036
Figure 4-6. FM Operation.
44,