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3.4.2.3. Input coupling switches AC/O/DC
In the DC position of the coupling switch the full bandwidth of the instrument
nents are displayed as trace shifts.
This may be inconvenient
tenuation of the signal will result in an attenuation
position of the coupling switch. In this position the d.c. component of the signal is inhibited
capacitor. Note that this capacitor also suppressestow frequencies, which meansthat some putse droop will
occur when low frequency square-wave signals are displayed.
In the O position of the coupling switch, the input signal is interrupted and the amplifier input is earthed,
enabling the O V reference of a trace to be readily determined.
3.4.3.
Triggering
To obtain a stable display of an input signal, the time-base must always be started on one fixed point of the
signal waveform.
Therefore, the time-base generator is started by narrow trigger pulses, formed in the trigger unit and controlled
by a signal derived from the vertical input channels, from the mains, or from an external source.
3.4.3.1.
Trigger coupling
The MTB trigger coupling
In the AUTO PP mode, the MTB trigger signal is a.c.•coupled, except when X DEFL is selected.
In TV mode the MTB trigger signal is d.c.•coupled.
In the TRIG mode and AUTO mode the trigger coupling is determined by the selection of the trigger coupling
switches TV, DC, LF and HF (S20).
The HF position inserts a high-pass filter for frequencies of 28kHz and higher, this pushbutton
used to reduce i.f.-interference
The LF pushbutton
(e.g. noise) and d.c.
When the DC pushbutton
signals from OHz and higher.
When TV is selected, the MTB LEVEL control is inoperative; the trigger level is fixed. The trigger signal is
d.c.•coupied
and the sensitivity
MTB
TRIGGER
MODE
AUTO
PP
AUTO
if small a.c. components of interest are superimposed on high d.c. voltages. Any at-
can be selected by the trigger coupling
e.g. hum.
inserts a band-pass filter for frequencies from 2Hz to 25kHz, reducing h.f.-interference
is selected, the trigger signal is direct-coupled
is adapted to TV signals.
MTB TRIGGER
TV
DC
DC
LEVEL
control
inoperative
of the small a.c. components. The solution is to use the AC
switches TV, DC, LF and HF.
and triggering can be obtained from
COUPLING
SWITCH
SELECTION
DC
AC
DC
Trigger bandwidth
DC: O ... IOOMHz
AC:
2Hz
... IOOMHz
LF: 2Hz
... 25kHz
HF:
25kHz
... IOOMHz
35
is available, and d.c. compo-
by a blocking
selection being
(S20)
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