45
Subject to change without notice
35
INPUT CH2
(BNC connector)
This is the CH2 signal input connector. It is a Y input in Yt and
XY mode. The connector housing is connected to the instru-
ment housing and thus to safety ground. The ring around the
connector is the probe identification contact, no voltage may
be applied here.
36
AUX
(pushbutton)
This pushbutton belongs to the AUXILIARY INPUT
38
. Depen-
ding on the current operating mode a menu may open after
pressing.
STOP
Attention!
This pushbutton has no function in analog and
digital mode if “External” is selected in the trigger
SOURCE
22
menu and does not open a menu.
36.1 Analog mode
36.1.1
The AUXILIARY INPUT serves as an input for external
trigger signals if after pressing the SOURCE
22
pushbutton the
function “External” has been chosen.
36.1.2
If ”External“ triggering was not selected the menu ”Z
Input“ will open up. If ”Off“ is chosen the AUXILIARY INPUT
has no function. If ”On“ is chosen it will function as Z input i.e.
intensity modulation input. This input is destined for TTL signals,
a voltage of
>
1 Vp will turn off the trace. They AC DC function
key is for Z input coupling selection.
36.2 Digital mode
In digital mode the AUX pushbutton is disabled and the AUXILI-
ARY INPUT
38
serves only as an external trigger input.
37
FFT pushbutton
(digital mode only)
Pressing the FFT pushbutton switches over to FFT, if digital Yt
mode is present.
Note:
In this state FFT mode can only be left by switching over
to analog mode. If digital mode is not to be left, please press
the FFT pushbutton again to display the FFT menu which offers
an Off function. Pressing the FFT pushbutton once again cause
the FFT menu to be displayed.
Note:
The signal can be input at CH1 or CH2. After pressing the
VERT/XY pushbutton
32
the channel can be selected. If DUAL
was present before, when switching to FFT, the channel that
previously served as trigger source is selected.
37.1 Window
There are different “windows“ available that cause different
signal data calculation and their display on the frequency axis.
After pressing the function key, the required “window“ function
(Hamming, Hanning, Blackman, Rectangle) can be determined
by the INTENS knob
2
. Please refer to the table below.
Note:
The FFT frequency resolution is the quotient of sampling rate
and the number of FFT points (4 kPts). At a constant number
of FFT points, the resolution is proportionally better as the
sampling rate is lowered. The Nyquist frequency is the highest
frequency a real time digital oscilloscope can measure without
aliasing. This frequency is half the sampling frequency (sam-
pling rate). In case of higher frequencies the number of samples
is too low. If the sampling frequency (rate) is possibly too low,
the readout displays ALS?.
37.2 Mode
The desired signal capture mode can be determined by the
INTENS knob
2
after pressing the function key. The following
modes are available:
37.2.1
Refresh
The signal capture is performed in real time refresh mode. The
result is displayed on the frequency axis (Yf).
37.2.2
Envelope
As in Yt mode frequency maxima and deviation are displayed
on the frequency axis (Yf).
37.2.3
Average
Shows the result of signal capturing processes after FFT cal-
culation and averaging.
37.2.4
Number
Determines the weighting accuracy of the FFT calculations in
the following averageing process. Numbers between 2 and 512
can be chosen by aid of the INTENS (2) knob which are displayed
by the readout (e.g. avg#256). The accuracy increases with
higher numbers but requires more time. Averaging enables
to reduce amplitude changes (noise) and frequency changes
(jitter) in the display.
37.3 Scale
The TIME/DIV-SCALE-VAR knob enables up to 20 fold X expan-
sion of the total spectrum display. This means that in case of a
span of e.g. 500 MHz, the span is reduced to 250 MHz if 2 fold
expansion is active; or 25 MHz span as the result of a 20 fold
expansion. The current center frequency setting is not affected
by scale factor changes.
On condition scale (X expansion), only a fraction of the spectrum
is displayed. The fractions lost can be made visible by turning the
HORIZONTAL knob, changing the center frequency setting.
37.4 dBV V(rms)
The amplitude unit can be selected by pressing the function key
and will be displayed with intensifi ed brightness.
V
rms
refers to 0 Volt (linear scaling of the Y axis) which is indica-
ted by the reference symbol at the left border of the graticule.
C o n t r o l s a n d R e a d o u t
Window
Criteria
Optimal for measurement of
H a n n i n g /
Hamming
Good / ideal frequency resolution but worse ampli-
tude resolution as at rectangle.
Hamming offers a slightly better frequency resolu-
tion than Hanning.
Sine wave, periodical signals as well as narrow band static
noise; transients or burst.
Blackman
Good amplitude, perfect frequency resolution.
Mono frequent signals for detecting harmonics of higher
order.
Rectangle
Best frequency resolution and lowest amplitude
accuracy.
Transients and bursts, settling time analysis; sine wave sig-
nals with equal amplitudes and stable frequency; broadband
static noise with relatively slowly varying spectrum.
