Is this purely related to the external trigger? Maybe this problem is related to the recovery time of the external trigger input somehow. What happens if you use a regular channel instead of the external trigger?
No, I first noticed it using a channel trigger.
The problem occurs on any channel that has the probe attentuation factor set to some value other than 1 V/V. In fact, the range of vertical scale factors for which the problem occurs increases for higher scale values.
For example:
2V/V, problem occurs at 10 mV/div
5V/V, problem occurs at 20 mV/div through 50 mV/div
10V/V, problem occurs at 40 mV/div through 200 mV/div
20V/V, problem occurs at 100 mV/div through 1V/div.
I can make it occur on any channel, and it follows the above pattern. It does not appear to be affected by signal amplitude, and the measured delay is always 600 ps when the problem occurs. This is using the scope measure delay function, so it a few ps longer than 600, same whether measured on rising or falling edges.
Only happens with inputs set to 50 ohm Zin.
I have replicated the results with rectangular pulses from my pulse generator.
It does not happen when I remove the cables from the RTO scope and put them on my SDA6020.
John