Oscilloscope - Pulse Mode & Auto Mode Trigger

[2X]

Hello,
I have the oscilloscope RTC1002 and I would like your opinions about a signal that I measured. I have the signal (Pictures 1 & 2) and the oscilloscope couldn’t trigger capture (stabilize) the waveform in auto mode. I set ON the oscilloscope function Hold-Off trigger mode; I measured the duration of the repetitive pulses and was 19,6uS, so I set the Hold-Off time at 20uS. Then the oscilloscope was triggered fine and the waveform was clear captured (without “ghost signals”) and stable (not moving like a train).

After the hold-off trigger mode I tried to capture the pulses of another slightly different waveform using this time the Pulse mode; I measured the duration of a single pulse (not all the pulses at this waveform had the same duration and are not total square with 90 degrees fall and rise transitions) and it was 192nS (Picture 3). I set the parameter of the Pulse mode function to trigger when it will find a signal smaller than 120nS (reference time). If I leave the Hold-Off enabled at 20uS the oscilloscope was triggered fine (Picture 5) on the first pulse were found with a duration smaller than 120nS, but the strange thing for me is that if I disabled the Hold-Off function the oscilloscope starts to show on the screen some “ghost signals” (Picture 4).
As I understand these “ghost signals” maybe must be due to the jitter effect, but why when I am on the Pulse mode and I turn off the Hold-Off time then only I saw these ghost signals? If the Pulse mode is active isn’t supposed that the auto trigger is no active and trigger only occurs under specific circumstances where have to do only with pulse duration? 

In the auto trigger mode as I know the trigger will occur even if a specific conditions of trigger level (independently of the trigger level that was set) doesn’t met, so there is a timer where waits about the specific trigger conditions to be met and if will not after a certain time?) the trigger will occur independently or there is a different mechanism/logic behind the auto trigger mode? This auto trigger time can be changed or just we go on normal mode to do that?

Pulse Mode Function - Manual Pages 52-53:
https://scdn.rohde-schwarz.com/ur/pws/dl_downloads/pdm/cl_manuals/user_manual/1335_7352_01/RTC_UserManual_en_07.pdf

[aliarifat794]

Auto-trigger mode is typically used when you want the oscilloscope to automatically trigger regardless of the input signal characteristics. It has a built-in timer that waits for trigger conditions to be met. The auto trigger time is usually fixed within the oscilloscope's firmware and isn't user-adjustable.