[Lorenfb]

A. "This is normally without consequence if the slope of the input signal if not too slow."

B. "The R5 value is not to be modified. The R6 value is determined at factory to set the triggering voltage at the zero crossing of the negative slope of the input signal (a bipolar pulse)"

C. "I am using a 2 V peak to peak sinus signal a a trigger. I s that appropiate.
If I increase that value to 8V pp the box works better due to a better signal to noise ratio.
This is not appropriate as the slope of such a sine wave is not fast enough not to be disturbed by the 3 kHz spurious signal."

What is all this nonsequitur stuff?????????

A. The purpose of using the Schmitt trigger is to make the input NOT
sensitive to the slope of the input waveform.

B. The triggering level is NOT set for zero crossing or it WOULD BE sensitive to
noise. The level is set to about 100mv.

C. A sine wave is MORE than appropriate as a trigger source for testing which
ALLOWS the tester to determine the input sensitivity.

Anymore guessing????????