Re: the apple test

On Wed, 1 Jan 2025 17:11:02 -0000 (UTC), Cursitor Doom
<cd999666@notformail.com> wrote:

On Wed, 01 Jan 2025 07:45:20 -0800, john larkin wrote:
>

On Wed, 1 Jan 2025 01:05:40 -0000 (UTC), Cursitor Doom
<cd999666@notformail.com> wrote:
 

On Tue, 31 Dec 2024 18:11:38 -0500, Edward Rawde wrote:
>

"john larkin" <jl@glen--canyon.com> wrote in message
news:sls8nj55tqh3u77h1vqbnvffs0vjjd7oo3@4ax.com...

On Tue, 31 Dec 2024 17:30:55 -0500, DJ Delorie <dj@delorie.com>
wrote:
>

john larkin <jl@glen--canyon.com> writes:

Close your eyes and imagine an apple in front of your face. Can you
see it? In detail, in color? Can you rotate it on any axis and see
it moving? Can you look down on it from the top and see which way
the stem points?

>
The important thing to remember is... there is no apple.

>
Apples are real.

 
Except imaginary ones.
 
But some imaginary things might be real.
https://www.youtube.com/watch?v=T647CGsuOVU

>
They're real alright. You can't describe things like complex impedance
or the plotting of a Smith Chart without recourse to them.

 
Certainly complex impedances can be visualized and analyzed in  time
domain. Better than in classic slide-rule-days RF terms.

>
There certainly is a highly useful role for TD in this area. In fact by
using a TDR and a VNA together one can disintangle multiple reflections on
a network and uncover discontinuities that are obscured by other
reflections. I really should get a TDR; it's about the only piece of test
kit (apart from a curve tracer) I don't own. Must remedy those
shortcomings as a priority!

TDR is a fabulous tool. You can see exactly where things are happening
on a board or in a box, and fix it there. That's really hard to do in
the frequency domain.

You can also investigate urban legends, like the terrible effects of
right-angle bends in PCB traces.

I don't have a curve tracer and don't miss it. The occasional subtle
semiconductor measurement can be done with bench instruments. A
classic curve tracer won't report capacitance-vs-voltage, or pA
leakages, or step-recovery, or any really interesting stuff.

Data sheets have curves.

It would be fun to have a small USB curve tracer that does measure
capacitances and fA currents.