Re: Puzzle of the day: 465b will not trigger on channel 2 SUCCESS!


Thank you Hank for your excellent explanation. The traces do indeed
stabilize if I bring them together. I was just expecting a stable
display with the same signal going into both channels. Looks like I can
close it up and call her done!


--- In, HankC wrote:


The LF trigger mode is working correctly.
When you try to trigger on 2 alternating traces, the signal going to
the trigger circuit includes a lower freq square wave, which is a
composite of the trace position of the 2 signals.
This lower freq square wave gets differentiated by the AC coupling to
the trigger circuit.
So, the trigger sees a differentiated spike with the vertical signals
riding on the differentiated slopes.
Note that the trigger instability improves when you position the 2
traces closer together.
This is because the "square wave" component of the trigger signal is
being reduced in amplitude.
Trigger off either of the signals & the problem will go away.
You could also try DC coupling but you may still have the problem.

"Chop" mode usually does not display this problem because the chop
rate is much faster than the Alt rate.
So, it doesn't get differentiated by the AC coupling to the trigger

The purpose of LF Reject triggering is to address this specific
You will not findLF trigger mode on a single-trace scope.

HankC, Boston

Join to automatically receive all group messages.