TM 11-5840-281-35/1
causes it to conduct more heavily, and diverts a portion
sawtooth. The cursor sawtooth generator stage consists
of the current that would normally flow through transistor
of current-adder transistor Q2610,
temperature-
Q2603. The reduced current flow through transistor
compensating
transistor Q2611, emitter-follower
Q2603 and resistor R2610 causes the voltage at the
transistor Q2612, and associated components
junction of resistor R2610 and capacitor C2602 to go
(2) The cursor sawtooth generator output is
more positive.
a variable slope sawtooth whose slope is proportional to
(3) This continuous process causes
the instantaneous antenna scan angle.
This is
capacitor C2602 to charge to an ever-increasing positive
accomplished by furnishing a variable current source to
voltage while keeping it in the linear portion of its
the current-adder stage in addition to the fixed -E
exponential charging curve. REF SAW LIN control
reference current. The additional variable current at
R2606 determines the amount of change in current
transistor Q2610 is the sum of the cursor angle no. 1
through transistor Q2603 for a given change in voltage
and cursor angle no. 2 currents. These currents
across capacitor C2602, and is adjusted to produce a
determine the slope of the cursor sawtooth. The output
linear ramp on the sawtooth. REF SAW SLOPE control
of the cursor sawtooth generator is taken at the emitter
R2609 is adjusted to set the peak voltage of the
of transistor Q2612, coupled through emitter-followed
sawtooth at 1.5 volts, measured at REF SAW testpoint
transsistor Q2613, and applied to the cursor trigger
TP2601. Temperature-compensating transistor Q2604
circuit.
e. Cursor Trigger Generator Circuit (fig. 7-12
is connected in the circuit such that when the emitter-
base voltage of transistor Q2603 tends to decrease with
and 7-6). The input to the cursor trigger generator circuit
an increase in temperature, an identical change will
is the cursor sawtooth from the sawtooth generator. The
occur across Q2604, since Q2604 is the same type of
cursor trigger generator consists of offset amplifier
transistor as Q2603. The change across transistor
transistor Q2704, cursor sawtooth comparator transistor
Q2604 clamps the base of transistor Q2603 to a new
CR2702, amplifier transistor Q2705, emitter-follower
potential proportional to the emitter-base voltage change.
transistor Q2706, and cursor trigger multivibrator
(4) The output of the reference sawtooth
transistors Q2707 and Q2708 on the sawtooth
generator is taken at the emitter of transistor Q2605,
comparator assembly.
coupled through transistor Q2606, and applied to the
(1) The cursor sawtooth comparator circuit
cursor trigger generator and cursor trigger cutoff gate
uses the negative resistance characteristic of tunnel
circuits.
diode CR2702 to provide a comparison between the
d. Cursor sawtooth Generator Circuit (fig. 7-12
reference and cursor sawtooth waveforms. These two
and 7-55). The input to the circuit is the cursor sawtooth
waveforms are applied across the resistor R2710 and
gate from the sawtooth comparator circuit. The cursor
tunnel diode CR2702 combination which is reverse-
sawtooth generator consists of AND gate transistors
biased by the current flowing out of offset transistor
Q2607 and Q2608; clamp transistor Q2609; sawtooth
Q2704. As the two sawtooth voltages-increase, the bias
generator transistors Q2610, Q2611 and Q2612; and
on the tunnel diode is reduced to zero and then becomes
emitter-follower transistor Q2613 on the sawtooth
forward-biased. As the forward bias on the tunnel diode
generator subassembly.
is increased, the current increases up to the peak current
(1) The negative 500-sec cursor sawtooth
point of the tunnel diode. A slight increase in bias
beyond this point causes the diode to move into its
gate is applied to transistor Q2607 where it triggers the
negative resistance region. The voltage across the
cursor sawtooth generator. In the quiescent state,
tunnel diode increases from about 0.07 volt to about 0.5
transistor Q2607 is conducting and transistor Q2608 is
volt, while the current decreases. This sudden increase
cut off. The voltage on the base of clamp stage
in voltage across the tunnel diode represents the cursor
transistor Q2609 is determined by the setting of OFFSET
solution and is applied through coupling capacitor C2712
CAL control R2638. OFFSET CAL control R2638 is
to amplifier transistor Q2705. The 12-volt negative-going
used to set the dc level of the cursor saw-tooth baseline,
waveform output of transistor Q2705 is coupled through
which is important to the calibration of the comparator
emitter-follower transistor Q2706 and used to trigger
circuit in the cursor trigger generator. When the cursor
multivibrator transistors Q2707 and Q2708. The output
sawtooth gate is applied, transistor Q2607 cuts off,
of the multivi-
which, in turn, cuts off clamp transistor Q2609. This
allows the cursor sawtooth generator to develop a
2-44
Previous Page
