Main Trigger Source; Input Impedance; Trigger Slope; Trigger Level - Tektronix 7B92A Maintenance Manual

Main Trigger Source

The MAIN TRIGGERING SOURCE pushbutton
switches select the source of the trigger signal that is
connected to the main trigger circuits.
INT. The INT pushbutton connects the trigger
signal from the amplifier plug-in unit. Further selection of
the internal trigger signal may be provided by the
amplifier plug-in unit or oscilloscope; see the instruction
manuals for these instruments for more information. For
most applications, the internal source can be used.
However, some applications require special triggering
that cannot be obtained in the INT position.
cases, the LINE or EXT positions of the SOURCE
switches must be used.
LINE. The LINE pushbutton connects a sample
of the power-line voltage from the oscilloscope to the
trigger circuit. Line triggering is useful when the input
signal is time-related (multiple or submultiple) to the line
frequency. It is also useful for providing a stable display
of a line-frequency component in a complex waveform.
Line triggering cannot be used when operating in the HF
sync triggering mode.
EXT. The EXT pushbutton connects the signal
from the MAIN TRIG IN connector to the trigger circuit.
The external signal must be time-related to the displayed
waveform for a stable display. An external trigger signal
can be used to provide a triggered display when the
internal signal is too low in amplitude for correct
triggering, or contains signal components on which
triggering is not desired. It is also useful when signal
tracing in amplifiers, phase-shift networks, wave-shaping
circuits, etc. The signal from a single point in the circuit
can be connected to the MAIN TRIG IN connector
through a probe or cable. The sweep is then triggered
by the same signal at all times and allows amplitude,
time relationship, or waveshape changes of signals at
various points in the circuit to be examined without
resetting the MAIN TRIGGERING controls.
EXT Þ 10. The EXT Þ 10 pushbutton operates
the same as described for EXT except that the external
signal is attenuated.
external trigger signals is desirable to increase the
effective range of the LEVEL control.

Input Impedance

The input Impedance of the MAIN TRIG IN and
DLY'D TRIG IN connectors may be selected by the front-
panel TERM switch.
Attenuation of high-amplitude
FRONT-PANEL IN -- 1 MΩ.
suitable
applications or when using a 10X probe.
position provides a high input impedance for minimum
loading on the trigger signal source.
FRONT-PANEL OUT -- 50 Ω.
recommended for high-frequency applications requiring
maximum overal bandwidth. The 50 ohm termination
should be used when externally triggering from a 50 ohm
system.
In such

Trigger Slope

(concentric with the MAIN TRIGGERING LEVEL control)
determines whether the trigger circuit responds on the
positive-going or negative-going portion of the trigger
signal.
operating in the high-frequency synchronization mode.
When the SLOPE control is in the + (positive-going)
position, the display starts on the positive-going portion
of the waveform; in the - (negative-going) position, the
display starts on the negative-going portion of the
waveform (see Fig. 1-4).
signal appear in the display, the setting of the SLOPE
control is often unimportant. However, if only a certain
portion of a cycle is to be displayed, correct setting of the
SLOPE control is important to provide a display which
starts on the desired slope of the input signal.

Trigger Level

determines the voltage level on the trigger signal at
which the sweep is triggered when operating in the Auto,
Norm, or Single Sweep modes.
control is set in the + region, the trigger circuit responds
at a more positive point on the trigger signal. When the
LEVEL control is set in the - region, the trigger circuit
responds at a more negative point on the trigger signal.
Fig. 1-4 illustrates this effect with different settings of the
SLOPE switch.
TRIGGERING MODE, COUPLING, SOURCE, and
SLOPE.
counterclockwise and rotate it clockwise until the display
starts at the desired point.
triggering level is available as the trigger signal frequency
exceeds 150 megahertz.
sync mode, the LEVEL control synchronizes the trigger
generator frequency to a sub-harmonic of the trigger
signal frequency.
selected.
1-10
Operating Instructions-7B92A
for most low- and
The MAIN TRIGGERING
The trigger slope cannot be selected when
When several cycles of a
The MAIN TRIGGERING
To set the LEVEL control, first select the MAIN
Then set the
When operating in the MAIN TRIGGERING HF
Trigger slope and level cannot be
The 1 MΩ position is
medium-frequency
The 1 MΩ
The 50 Ω position is
SLOPE control
LEVEL control
When the LEVEL
LEVEL control fully
Less selection of the
REV A, JUN 1978