Signal at the generator

First, i examined how the scope sees the function generator's output. This is with a 500 Ohm resistive probe, sample rate at 400MSa/s, 10MHz (left) and 25MHz (right) signals. The nominal amplitude was 3.3V and the function generator's rise/fall time is specified as less than 10ns:

As expected, the result looks quite decent. Next, I used a 5kOhm resistive probe:

There is a bit more bounce on the signal, but it's still fairly calm. Now I switched to the scope's standard capacitative 1:10 probe:

Quite clearly, those electrons are beginning to have a party. Finally I've attached the LA probe, digital threshold set to 8V:

Not pretty.

Input signal versus synchronization

In the following experiments, I've removed the analog probe to keep it from polluting the signal. In order to still have an idea of what's happening in the analog domain, I added the function generator's sync output, whose rising edge precedes the rising edge of the square wave by about 20ns. This is shown in the following screenshot:

The yellow curve is the input to the LA, the blue curve is the sync output of the function generator, and the red curve is what the LA imagines is happening at the 8V threshold.

LA test

Since 25MHz promised a lot of trouble, I tried 1MHz and 10MHz. These are the results for 1MHz, with the digital threshold set to 1.5V, 2V, 3V when we're lucky, 3V when we're not, 4V, and 8V:

The 1.5V and 2V results were good enough that I enabled persistence to show how many glitches I got. There was a small number at 2V while 1.5V is clean. 3V varied between great and awful.

The scope shows "<5Hz" for the trigger frequency in the 3V cases and the 8V case because I had set it to single sweep. In all other cases, it was set to normal sweep.

And here's the same show for 10MHz, 1.5V, 2V, 3V, 4V, and 8V: