Tektronix 7D11 DIGITAL DELAY Service Instructions Manual page 14

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Fig_ 1 -5 . Location of Z·AlIIis Blanking Oisp lay switch (on lef! side
of ',,$I,umend. T he switch posi t ion towards tho 'ear of Ih l unit
selects Z-axis blanking.
NOTE
At faster sweep speeds (100 nsldiv or faster) care
must be taken when illterpreting CRT display because
relative propagation delays through the lOl l and
vertical amplifier plug-ins are not the same. This
appears as a relative rfme shift between delay in terval
pedeswl or Z-axis blanking generated by the 7011
and the signal(s) viewed through a vertical amplifier
on the CRT. Changing the TRIG SOURCE between
INT and EXT or EXT
+
10 will vary this apparent
time shift due to differences in propagation delays of
the signal path.
OPER A T ING MODE S
Sweep Delay
The 7 D 11 can be used to delay the start of a sweep fo r a
selected time interval fo llowing the receip t of a trigger.
Low ·jitter sweep delay can be used for accu rate time, jitter,
and stability measurements. Sweep delay can also be used
to select a portion of a complex signal for display . A sweep
is delayed by triggering the
~ eep
from the Delayed Trigger
output of
the 70 II ,
rather than from the signal to be
displayed. Several methods of coupling the Delayed Trigger
to the sweep are possible, depending on the appl ication.
These methods are described in the following discussions.
B Sweep Delay Mode Switch . The sweep produced by
a
time-base unit can be controlled and delayed by a 701 1 via
the mainframe interface and the 8 SWEEP DELAY MODE
swi tch. To use this mooe 0 1 sweep delay,
the 701 1
must be
installed in the A Horizontal compartment and the time-
base unit in the 8 Horizontal compartmen t of a four.plug-in
mainframe. For further information, see B Sweep Delay
Mode.
Operating Information- 7D11 Service
NOTE
The logic levels provided to the 7D II from the
mainframe are designed to con trol a time-base unit
delaving sweep. For this reason, tIle 7DI I might
become locked out (no output) when the setting of
either the B-Sweep unit Time/Division switch or rhe
B SWEEP DHA Y MODE switch is changed. If this
occurs, a delayed sweep will not be produced. To
rese t the 7D11, set the B SWEEP DELA Y MODE
switch firs t to INDEPENDENT, then select the
desired delay mode.
Inte rnal Trigger. The sweep produced by a time·base
unit in a horizontal compartment can be internally trig.
gered from a 7 011 in a vertical compartment. To use this
sweep dela y mooe, the 70 11 must be selected by the
mainframe trigger source switch. Delaying a time·base
sweep from the internal source can be used with the units
installed in either a three- or fou r.plug-in mainframe.
External Trigger Source. A sweep can be delayed by
external triggering from the OLY'D
TRIG
OUT connector.
This methoo can be used w ith any triggered sweep.
Echo Delay Tim e Mode
The Echo delay time mooe provides a CRT readout of
the "one·way-trip·' time, or one·hall o f the generaled delay
time. Th is mode o f operation is selected for use by an
internal swi tch (on leh side
of unit. see
Fig. 1-6). In the
Echo mode, the delay time is selected by the DELAY TIME
OR EVENTS control in 200·nanosecond increments. An
insertion delay of about 160 nanoseconds in this mode
requ ires adding analog delay time to the first delay
increment to obtain a 2QO·nanosecond delay interval. This
can be accom plished by displaying the OELA Y INTERVAL
OUT and setting the FINE DELAY dial fo r a tolal delay
interval o f 200 nanoseconds as measured on the graticule.
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Filii.
l~ .
l oca tion of No.mal ·Echo Delav T.m e Mode sw itch Ion
left side of unitl. Slit the sw;teh towards th a fronl of the unit to
sele.;t Normal Mod e.
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