Wavetek 2001 - 5.5.7 Relationship Between Voltages

MAINTENANCE
Model 2001
Figure 5-1 1. Ml H Bal Adjustment
- -16V
ADJUST WAIT
. Figure 5-12. Sweep Ramp
5.5.7 RELATIONSHIP BETWEEN +16, -16, SWEEP RAMP
and INVERTED SWEEP RAMP
The next step
is possibly the most critical to the overall
performance of the generator and requires some explanation.
The frequency accuracy of the unit is dependent on the
+16
volt reference supply, the -16 volt reference supply, the 32
volt peak-to-peak sweep ramp and the inverted 32 volt
sweep ramp. These four voltages must be precisely adjusted
in relation to each other to maintain dial and display
accuracy.
+16V (REMOTE
JACK, PIN 2)
SWEEP RAMP
(REMOTE JACK, PIN 10)
INVERTED SWEEP RAMP
(REMOTE JACK, PIN 15)
-16V (REMOTE
JACK, PIN 3)
Figure 5-13. Relationship Between Sources
The + and -16 volt references can easily be set up accurately
as already described in paragraphs
5.5.4 and 5.5.5. The
next problem is to adjust the peak "positive and negative"
excursions of the sweep ramp,
M1H pin 12, to within 0.1
volt of the +16 volt and -16 volt references.
Since the entire
32 volt change from -16 to +16 volts is
equivalent to a frequency change of 520 MHz, the 0.1 volt
ramp accuracy would be equivalent to a frequency error,
due to the program voltage, of
1.6 MHz, which is allowable.
It can be seen in the initial adjustment of the sweep ramp,
made in paragraph
5.5.6, that the required 0.1 volt resolu-
tion when viewing the entire
32 volt sweep ramp is not ob-
tainable. Offsetting the scope position control to view only
the positive or negative peak is not practical since the
M1H
CENT and SIZE adjustments vary both the positive and
negative peaks.
A practical approach is to use a scope
probe containing
two back-to-back 12 volt zener diodes
in a zero
supressing circuit. The schematic of the probe is
shown in Figure
5-14.
TO CIRCUIT~TTO SCOPE VERTICAL INPUT
Figure 5-14. Zero Suppressing Probe
-
MAINTENANCE
-
Figure 5-11. M1H Bal Adjustment
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(
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-- -
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.... -
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...
j
V
-
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-
~
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--+16V
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V-
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---I6V
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ADJUS
TO
..... w,", /' I L
FOIl 1_. -l
T CLAMP
-16V
Figure 5-12. Sweep Ramp
5.5.7 RELATIONSHIP BETWEEN +16, -16, SWEEP RAMP
and
INVERTED SWEEP RAMP
The next step is possibly the most critical to the overall
performance of the generator and requires some explanation.
5-10
Model 2001
The frequency accuracy of the unit is dependent .on the +16
VQlt reference supply, the -16 VQlt reference supply, the 32
VQlt peak-tQ-peak sweep ramp and the inverted 32 VQlt
sweep ramp. These fQur vQltages must be precisely adjusted
in relatiQn
tQ each .other tQ maintain dial and display
accuracy.
/
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/
/
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,
......
'.:-,;
/
V
:\.-
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"-
/
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~
~~
¥ ~
V
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L..
f'
l-
i----!
'C'
......
/
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'\V
~
+16V (REMOTE
JACK, PIN 21
SWEEP RAMP
(REMOTE JACK, PIN 101
INVERTED SWEEP RAMP
(REMOTE JACK, PIN lSI.
-16V IREMOTE
JACK, PIN 31
Figure 5-13. Relationship Between Sources
The + and -16 VQlt references can easily be set up accurately
as already described in paragraphs 5.5.4 and 5.5.5. The
next prQblem is tQ adjust the peak "PQsitive and negative"
excursiQns .of the sweep ramp, M 1 H pin 12, tQ within 0.1
VQlt .of the + 16 VQlt and -16 VQlt references.
Since the entire 32
VQlt change frQm -16 tQ +16 VQlts is
equivalent tQ a frequency change .of 520 MHz, the 0.1 VQlt
ramp accuracy WQuid be equivalent tQ a frequency errQr,
due tQ the program vQltage, .of 1.6 MHz, which is allQwable.
It can be seen in the initial adjustment .of the sweep ramp,
made in paragraph 5.5.6,
that the required 0.1 VQlt resolu-
tiQn when viewing the entire 32
volt sweep ramp is not .ob-
tainable. Offsetting the scQpe PQsitiQn cQntrQI tQ view .only
the PQsitive .or negative peak is nQt practical since the M 1 H
CENT and SIZE adjustments vary bQth the PQsitive and
negative peaks. A practical apprQach is tQ use a SCQpe
prQbe cQntaining twQ back-tQ-back 12 VQlt zener diQdes
in a zero supressing circuit. The schematic .of the prQbe is
shown in Figure 5-14.
12V 12V
TO CIRCUIT---1I1\.---~"--TO SCOPE VERTICAL INPUT
Figure 5-14. Zero Suppressing Probe