User Manual

13.3. Nyquist frequency
The highest frequency that any Real Time Digital Oscilloscope can measure is exactly half of the sampling rate
under the condition of no mistakes, which is called Nyquist frequency. If under-sampling occurs when the
frequency sampled is higher than Nyquist frequency, “False Wave” phenomenon will appear. So pay more
attention to the relation between the frequency being sampled and measured.
Note:
In FFT mode, the following settings are prohibited:
1. Window set;
2. XY Format in Display SET;
3. “SET 50%” (the triggering level at the vertical point of signal amplitude) in Trigger setting;
4. Measure.
Digital Filter (Only P 1245/1255/1260)
• Low-pass filter: Pass signals with a frequency lower than a certain cutoff frequency and attenuates
signals with frequencies higher than the cutoff frequency.
• High-pass filter: Pass signals with a frequency higher than a certain cutoff frequency and attenuates
signals with frequencies lower than the cutoff frequency.
• Band-pass filter: Pass frequencies within a certain range and attenuates frequencies outside that
range.
• Band-reject filter: Pass most frequencies unaltered, but attenuates those in a specific range to very
low levels. It is the opposite of a band-pass filter.
• Cut-off frequency: A frequency characterizing a boundary between a passband and a stopband. For
example, as defined by a 3 dB corner (a frequency for which the output of the circuit is −3 dB of the
nominal passband value).
• Order: The order of a filter is the degree of the approximating polynomial and in passive filters
corresponds to the number of elements required to build it. The higher the order, the more the filter
will approach the "ideal" filter; but also the longer the impulse response is and the longer the latency
will be. When the high frequency and low frequency of the input signal differ significantly (i.e., 500 Hz
– 50 kHz), the order can be set to a small value, such as 29 to 35. When the difference between the
high frequency and low frequency is small (i.e., 10 kHz – 50 kHz), the order should be set to a larger
value, such as 128.
14. Application of VERTICAL POSITION and VOLTS/DIV Knobs
1. The VERTIVAL POSITION knob is used to adjust the vertical positions of the waveforms of all Channels
(including those resulted from the mathematical operation).The analytic resolution of this control knob
changes with the vertical division.
2. The VOLTS/DIV knob is used to regulate the vertical resolution of the wave forms of all channels
(including those obtained from the mathematical manipulation), which can determine the sensitivity of the
vertical division with the sequence of 1-2-5. The vertical sensitivity goes up when the knob is rotated
clockwise and goes down when the knob is rotated anticlockwise.
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