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The NI 5114/5122/5124/5142/5152/5153/5154 has two filter selections, LF Reject and HF Reject, available for all analog trigger sources. These are defined as trigger coupling options. Both are single pole filters, with the cutoff frequency set to 50 kHz.
An example application for the LF Reject is in triggering on a 455 kHz IF signal in the presence of line cycle noise. If the 50 or 60 Hz line signal has sufficient magnitude, it causes triggering and timing errors versus the desired 455 kHz signal. This can be a challenging signal to use as a trigger. Using the 50 kHz highpass filter, the 50 or 60 Hz component is attenuated by nearly 60 dB, greatly improving the trigger stability and jitter performance of the acquisition.
An example application for the HF Reject is triggering on a 1 kHz Sigma-Delta integrator output in the presence of high-frequency signal content, including overshoot and ringing on the transitions. When this high frequency content crosses over the trigger threshold, false triggers occur. Using the 50 kHz lowpass filter, you can reject the high-frequency content, noise, and overshoot to obtain a clean trigger source.