HPS50 trigger

Hello,

I am trying to get the HPS50 trigger on random pulses, roughly 4 V in height, 10 micro-sec in length (gaussian shaped). Whether I have the trigger in “norm” or “run” does not make any difference, the scope triggers continuously. In “norm” I move the trigger up and down without any effect. If I bring the trigger well below the baseline of the signal, the triggering will stop.

Is there a setting that I am missing?

Thank you for your help.