Model 5340A
Theory of Operation
A negative level at pin 8 turns U2 and U4 off which turns
off
Q1. Q1 determines when the search
ramp signal
is
routed to DC Compensation Amplifier A7. The search ramp signal
is
derived from
the search pulse signal which is supplied from Search Programmer A6.
U1 and U3 function
as
an
integrator to provide a ramp voltage output. C7
is
the integrating capacitor and R15 sets the dc
level for the ramp signal.
4
-
156. A6 SEARCH PROGRAMMER ASSEMBLY, 05340
-
60004
4
-
157. The Search Programmer (Figure 8
-
12) determines the search ramp amplitude and sets
the loop gain compensation. The circuits consist of counter U4, binary to decimal decoder
U2,
buffer U1, loop compensation switches Q1 through Q6, search programming switches Q7
through
Q12, and pulse conditioner
U5.
4
-
158. Pulse conditioner U5
is
a
one
-
shot multivibrator used to shape the incoming start search
pulse from A21.
C1 and
R3
set the multivibrator pulse width
at
5 milliseconds. The prf
is
deter
-
mined by Control Assembly A21. The conditioned pulse
is
used by the Search Assembly A5 to
derive the search ramp signal.
4
-
159. The counter circuit U4 receives three
-
line binary data and a strobe from interface
assembly
A19. In addition, U4 receives the inhibit control and
start
search signals from A21.
These are used to drive the clock
2
input and the reset input of U4. The strobe input allows
parallel
-
entry for the DB, DC, and DD inputs. When the strobe line receives
a
logic
0,
the data
inputs are transferred to the D,
C,
and B outputs (U4 pins 12, 2, and 9). Counting occurs on the
negative going edge of the input clock pulse. The count function will
start
from the number
strobed in or will start from zero when the counter is reset. The outputs are binary and connect to
a
binary
-
to
-
decimal decoder U2. U2 provides
a
decimal output between
0
and 6. As an example
of operation, assume that U2 receives
A=H, B=H, and C=L. With this input, the 3 line (pin
4)
goes
low to drive
Ul(4) high.
With
Ul(4) high, Q4 and QlO are on and all other FET’s are off. For
this programming segment,
R11, C8, and R19 provide the proper loop compensation and R25
sets the search amplitude. Two modes of operation can be selected, normal and programmed.
4
-
160. A7 DC AMPLIFIER/COMPENSATOR NO.
1
ASSEMBLY, 05340
-
60005
4
-
161. A7 (Figure 8
-
13) consists of lock mode switches Ql, Q2, Q3, Q6, and dc amplifiers
U1
and
Q4, Q5, QS, Q9. The lock mode switches are controlled by the search switch signal from A5 and
the input loop lock from
A5.
The output
from
Phase Detector
No.
1
represents the error signal
required to drive VCO
No.
1
to be phase coherent with the
20
MHz reference signal. When Q2 is
on, the phase detector signal
is
amplified by U1.
R13 sets the dc level output. R27 sets the gain
of
Q4
and
QS.
Diodes
CR5
and
CR8
provide
limits
for
the
maximum
dc.
4
-
162.
A8
BANDPASS FILTEWPHASE DETECTOR ASSEMBLY, 05340
-
60006
4
-
163. The BPF/Phase Detector Assembly (Figure 8
-
14) consists of
a
bandpass filter amplifier
U1, comparator U2, retriggerable one
-
shot multivibrator U3B, sampler driver U3A, sampler Q2,
and high impedance amplifiers
Q1A and Q1B.
A8 receives the 20 kHz reference signal
from
Time Base A20 and the 20 kHz mixer signal from Mixer All. A8 produces two outputs: the trans
-
fer loop SEARCH signal and the phase detector 2 signal. The transfer loop SEARCH signal
is
sent to DC Compensator Amplifier A9.
A9 uses the transfer loop SEARCH signal
as
an indi
-
cation of loop lock. The phase detector 2 output is used to drive VCO 2
so
that the 20 kHz mixer
signal
is
coherent with the 20
kHz
reference signal.
4
-
164. The input to’Ul‘,is the mixer output from All
at
approximately 1V peak
-
to
-
peak
amplitude.
U1
is an operational amplifier connected in a bandpass filter feedback configuration.
The filter is tuned to 20
kgz with a Q of about
2
and a bandpass of
*5
kHz
at
the
3
dB points.
4
-
165. Comparator u2 compares the output level of U1 with the positive level set by R13. When
the output level
of
U1 exceeds the level set by R13, U2 produces
a
positive output to trigger U3B.
U3B is a retriggerable one
-
shot multivibrator. When U3B pin 12 goes high, the multivibrator
triggers to drive U3B pin 10 high for approximately
50
psec.
The duration of the 50
psec
,
:i
4
-
39
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