User Manual

32
Figure 29 Bandwidth and Nyquist frequency
In practice, an oscilloscope's sampling rate should be four or more times its bandwidth: f
S
= 4f
BW
.
This way, there is less aliasing and the aliased frequency components have a greater amount of
attenuation.
4.3 Memory Depth
Memory depth refers to the number of points sampled from the waveform that the oscilloscope
can store in a single trigger sample. It directly reflects the amount of sample memory. The
oscilloscope provides up to 14 Mpts memory depth (7 Mpts if two channels are being displayed).
To change the memory depth
1. Press the Acquire button on the front panel.
2. Press the Mem Depth softkey.
3. Turn the Universal Knob to select the desired value and press the knob to confirm.
4. Pressing the Mem Depth softkey repeatedly can also select the desired value. The current
memory depth is displayed in upper-right corner of the screen.
The following equation relates memory depth D (in samples), sampling rate R (samples per
second), and waveform length T (seconds):
 = 
Limiting the oscilloscope bandwidth (f
BW
) to 1/4 the sample rate will reduce frequencies above
the Nyquist frequency.
Aliased frequency
components
Attenuation
f
S
/4 f
N
f
S
-3dB
Frequency
0dB
Limiting oscilloscope bandwidth (f
BW
) to ¼ the sample rate (f
s
/4)
reduces frequency components above the Nyquist frequency (f
N
).