how to troubleshoot?

[patchell]

    I have a digital scope at work, don't remember the model number, but a
500MHz BW, 1GS/s Tek scope.  Real nice scope......BUT....aliasing can be a real
problem.  A good example is what I am doing right now.  I am trying to track
down an oscilation in a power amplifier that drives a three phase motor.
Depending on how I set the sample rate, the display looks completely
different.  The oscilation is about 1MHz and the signal that is supposed to
come out is 500Hz.  The oscilation can look real funny, depending on how close
it happens to be to a ratio of the sample rate.  I generally have to turn the
sample rate knob (which also sets the equivalent to the sweep rate) in order to
make sure I get a "good idea" of what is really going on.  I have gone down
many blind alleys because I failed to realize that the scope was lying to me.
Analog scope don't have this problem.  Still, as long as you know that the
digital scope will lie, you can be careful.

    Personally, my home scope is an analog.  It is only 20MHz bandwidth, but
that seems to be more than adequate for synth work.

    -Jim

Lincoln Fong wrote:

> >>However if you got cash to spend get a digital so u can upload upload the
> results to the pc/mac(now were talking 1000$ range)
>
> I have always used analogue scopes and whilst talking about upgrading the
> other day with a friend he mentioned that a good analogue is sometimes
> better than a digital. I think it was something to do with the quantisation
> causing difficulty taking readings(?). Do you scope afficianados have a
> preference? Its mainly for audio work which may have an influence. My
> current one is 20MHz.
> pc uploading is not necessary.
>
> Lincoln
>
> Ps without wanting to start another acronym bonanza what does AFAIK stand
> for???

--
 -Jim
------------------------------------------------
* Visit:http://www.silcom.com/~patchell/
*-----------------------------------------------
*I'm sure glad Merry Christmas comes just once a year
* -Yogi Yorgensen
------------------------------------------------