HP 54600B User, Installation And Service Manual page 56

Low frequency reject (LF reject) adds a high pass filter with the 3-dB point
at 50 kHz (see figure 2-20). Use LF reject to remove low frequency signals
such as power line noise from the trigger path.
Figure 2–20
0 dB
3 dB down point
dc
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.
Figure 2–21
Random noise on the displayed waveform
To reduce the random noise on a signal
Pass
Band
50 kHz
Operating Your Oscilloscope
2–29