Low-frequency reject (LF reject) adds a high-pass filter with the 3-dB point
at 50 kHz. Use LF reject to remove low-frequency signals, such as power line
noise, from the trigger path.
LF Reject
Noise reject increases the trigger hysteresis band. By increasing the trigger
hysteresis band, you reduce the possibility of triggering on noise. However,
this also decreases the trigger sensitivity so that a slightly larger signal is
required to trigger the oscilloscope.
Random Noise on the Displayed Waveform
3 dB down point
Pass
Band
dc
0 dB
50 kHz
Figure 5-5
Figure 5-6
Making Measurements with HP 54645A/D Oscilloscopes
To reduce the random noise on a signal
5-9
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