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Understanding trigger specifications

Question asked by deninnh on Jan 22, 2015
Latest reply on Jan 23, 2015 by deninnh
I've been using scopes for over 30 years up to the latest and thought I knew them fairly well.  I've purchased several high end scopes in the past and have to admit that trigger specifications were not high on my list of concerns.  They just worked !

After acquiring a personal 54846A which will not trigger above 1GHz on a clean sine wave (Agilent source), I decided I should read the spec.

It was surprising to find that trigger sensitivity for this 2.25GHz scope is only spec'd up to 1GHz.

So then what happens ?

Funny thing is that it *will* trigger on very fast events like an avalanche pulser or airborne ESD event (from a distance of course) with risetimes below 200ps.  But it just can't handle a sine wave.  I've looked at the source output and it is very clean spectrally.  On another 3GHz scope, the sine wave is perfect.

Is the scope broken?  All channels are identical in behavior.  Deleted cal files and ran full cal with no change.  Unit is very clean and has the last software version offered and also the last, fastest motherboard.

I realize that current  models have much improved triggering.  On another unmentioned brand of scopes I've always been able to trigger right up to the specified scope bandwidth before aliasing and other things kick in.  

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