Triggering; Source - Tektronix 7D20 Operator's Manual

Operating Instructions-7D20
Section 3 .) The resultant effect on bandwidth is shown in Table 2-4 . It is important
to note that in all digitizers, digitized signal frequencies which exceed the Nyquist
limits will be aliased . The Nyquist frequencies for each digitizing mode are indicated
in Table 2-4 .
In the ROLL digitizing mode the TRIG'D light does not illuminate because triggering
is not used . An exception to this is when HOLD NEXT is used in the ROLL mode .
Refer to the discussion of the HOLD NEXT function later in this section . The
following discussions explain the triggering functions and how they are used .
SOURCE
TRIGGERING
The triggering features of the 7D20 are functionally grouped into three categories ;
SOURCE, COUPLING, and MODE . The associated triggering keys are arranged in a
sequence which places the most-often used selections at the top of each column of
keys . With this arrangement, stable acquisition and display can usually be obtained
by pressing the top keys : P-P, AC, and MODE . When an adequate trigger signal is
applied and the LEVEL control is correctly set, triggered acquisition is indicated by
an illuminated TRIG'D indicator . If the TRIG'D light is not on, the trigger signal
amplitude is inadequate, or its frequency is below the lower frequency limit of the
AC coupling, or the 7D20 may be in HOLD . If proper acquisition is not obtained with
these keys, other selections must be made .
Keys in this column select the source of the trigger signal . The keys illuminate when
selected .
MODE-The MODE key causes the trigger source to be determined by the AOR
MODE selection . If the AOR MODE is channel 1, then the trigger source is also
channel 1 . If the AOR MODE is set for channel 2, then the trigger source will
automatically set to channel 2 . If the selected AOR MODE is ADD or BOTH the
trigger source is forced to be channel 1 . When MODE triggering is selected the
appropriate CH1 or CH2 key will also illuminate . SOURCE MODE will cancel if
another selection; CH1, CH2, LINE, or EXT (+10) is made .
CH1-This key permits you to select the channel 1 input for the trigger source . The
key illuminates when selected and causes the trigger signal to be obtained from the
signal applied to the channel 1 input . This provides a stable display of the signal
applied to the channel 1 input.
CH2-This key permits you to select the channel 2 input for the trigger source . The
key illuminates when selected and causes the trigger signal to be obtained from the
signal applied to the channel 2 input . This provides a stable display of the signal
applied to the channel 2 input .
LINE-Selection of LINE SOURCE connects a sample of the power-line voltage
from the host mainframe to the trigger circuit . Line triggering is useful when the
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