Re: Help with Oscilloscope - Missing lines?

"Dave Nubury" <remove_me_david_nugent@xxxxxxxxxxx> wrote in
2JW8e.39108$vt1.25150@edtnps90:">news:2JW8e.39108$vt1.25150@edtnps90:

> Just picked up a used scope. 20MHz.. - Supposed to be in great
> working condition. Came with no leads.
> I just attached a couple of aligator clips to the input (Ch1) for now.
>
> It seems to show AC fine. (Nice sine wave)..
>
> However if I try to watch 5volt logic pulses from different sources,
> the vertical line in the state changes seems
> to be missing. For example. i would expect to see something like:
> ______ _____ _____
> | | | | | |
> __| |____| |____| |__
>
> but what I'm seeing is:
>
> _____ _____ _____
>
> _____ _____
>
> Is this normal? Does it have something to do with not having a probe
> maybe? Crapy scope?
>
> I would appreciate any info.
> Thanks
> Dave
>
>

The rise time of the input signal is too fast for the CRT phosphor to
visibly display at the chosen sweep speed.The E-beam is moving much faster
in the vertical axis than the horizontal axis,thus less time for the
phosphor to absorb the beam energy,thus the phosphor absorbs much less
energy,with resultant lower light output.If you looked while in a darkened
room,or with an image-intensifier,you might see the rising edges.
Some phosphors are better than others for certain conditions.
Phosphor choice is always a compromise.

--
Jim Yanik
jyanik
at
kua.net
.