40
Subject to change without notice
displays will be visible. With ”Zoom only“ only the expanded
display will show up.
The Zoom time base speed will be indicated in the readout
”Z:...“ and is calibrated. Turning the knob CCW will decrease
and turning it CW will increase the time base speed. This can
be selected from 20 ms/cm to 5 ns/cm in a 1-2-5 sequence.
The maximum expansion is 50,000 times (”A:10ms“ and
”Z:200ns“.)
28.3 XY digital mode
As XY mode is untriggered, all trigger related controls (LEVEL
A/B
19
, MODE
20
, FILTER
21
and SOURCE
22
are deactivated.
The same applies regarding the ZOOM function (HOR VAR
30
and
X POS DELAY
26
), the X magnifi er (MAG x10) and all functions
not meaningful in XY mode.
STOP
Attention!
The TIME/DIV-SCALE-VAR knob
28
is active, be-
cause sampling is required in digital XY mode and
consequently the sampling rate must be set. Thus
the readout displays the sampling rate but no time
defl ection coeffi cient.
It is recommended to choose a suitable sampling rate in Yt
mode and then switch over to XY mode. A suitable sampling
rate is when both signals are displayed with one complete signal
period. With increasing number of displayed signal periods a
degradation of the XY signal display takes place.
28.4 FFT (digital mode)
28.4.1
Preliminary note:
To avoid erroneous spectrum displays, it must be checked
before selecting FFT, that the Yt (time base) signal display is
suitable for calculation in FFT. This means that the time base
setting (sampling rate) must enable the display of minimum one
signal period; with complex signals this is regarding the signal
with the lowest frequency. On the other hand the sampling
rate must not be too low (to many signal periods) to avoid so
called aliasing. The signal display height should be between 5
mm (0.5 div.) and 8 cm (8 div.). Signal display heights
>
8 cm,
cause the danger that the dynamic range is exceeded, so that
signals deformed by limiting effects to square wave form,
become digitised and at least show spectrum displays spectra
that do not exist in reality. If the sampling rate is too low the
readout displays “ALS“; if the signal is too high “overrange ±“
will be displayed.
Such problems can be avoided, by pressing the AUTOSET push-
button
11
before switching over to FFT or during FFT mode.
28.4.2
Scaling:
For better understanding in some cases the term sampling
frequency is used instead of sampling rate although the readout
displays the sampling rate. A sampling rate display of 40 MSa
(40 Megasamples per second) is the equivalent of a sampling
frequency of 40 MHz.
The current sampling rate setting in Yt (time base) mode auto-
matically sets the center frequency and span in Yf (FFT) mode
after switchover from Yt (time base) to Yf (FFT) mode. In FFT
mode the TIME/DIV.–SCALE–VAR can be used for changing the
span (SCALE function, expanding the frequency axis) and not
the sampling frequency setting.
The readout displays the sampling rate, center frequency and
span setting together with other parameters in FFT mode. From
the sampling frequency (rate) setting the theoretically highest
displayable frequency (f
max
) results. In accordance with the
Nyquist-Shannon sampling theorem, the highest frequency to
displayed must be 2 * f
max
. At a sampling rate of 1 GSa/s – cor-
responding to a sampling frequency of 1 GHz – the maximum
displayable frequency is below 500 MHz (1 GHz / 2). In practice
the frequency response of the oscilloscope must be taken into
account (e.g. 100 MHz –3dB); this means that the voltage height
of a 100 MHz is displayed with 0.707 V although the real value is
1 V. This error becomes larger with even higher frequencies.
The center frequency corresponds with the vertical graticule line
in the screen center with direct relation to the frequency span
that displays the frequency range from the left to right graticule
border lines. The display “Center:10.00MHz“ and “Span:20.0MHz“
indicates that the left graticule border line coincides with 0 Hz, the
vertical center line with 10 MHz and nearly 20 MHz are displayed
at the right border line. Under these conditions the sampling
frequency is 40 MHz (Readout: 40 MSa).
29
MAGx10
(pushbutton)
In analog mode only: pressing this pushbutton will turn on the
x 10 magnifier. No menu will be shown. If ”x10“ is illuminated
on the MAG pushbutton the magnifier is activated. The adjusted
time/cm will be shown in the top left readout. Depending on
the time base mode turning on the magnifier will have these
effects:
29.1 ”Time base A only“
The display will be expanded around the screen centre by a
factor of 10, the time/cm indication adjusted accordingly.
29.2 ”Search“
(A and B times bases alternated)
The time base A speed will not be affected. The time base B
speed will be increased by a factor of 10, hence the time base
B display will be expanded 10 fold in X direction.
29.3 ”B only“
The time defl ection coeffi cient reduces by factor 10 causing a
tenfold X magnifi cation (signal expansion).
30
HOR VAR
(pushbutton)
This pushbutton will open the ”Time base“ menu, the contents
of which depend on the operating mode selected.
30.1 Analog mode
The following modes are available:
30.1.1
A only
In this setting only time base A is active and thus in the top left
position the readout displays only “A....“. The TIME/DIV-SCA-
LE-VAR knob
28
only effects time base A. By aid of the MAG
x10 pushbutton
29
the signal display can be expanded 10 fold;
reducing the time defl ection coeffi cient by factor 10.
If the mode is changed from time base A to ”Search“ or ”B only“
all settings of time base A remain intact including triggering.
30.1.2
Search
This mode implies alternate time base operation. The readout
will show the speeds of both time bases (”A...“ and ”B...“). The
TIME/DIV-SCALE-VAR knob will set the time base B speed.
In alternate time base mode part of the time base A display will
be intensified. The horizontal position of the intensified portion
may be shifted using the HORIZONTAL knob
27
, provided its
function was set to ”Delay“, this is the case if the X-POS DELAY
C o n t r o l s a n d R e a d o u t
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