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From: john larkin <JL@gct.com>
Newsgroups: sci.electronics.design
Subject: Re: the apple test
Date: Wed, 01 Jan 2025 09:47:09 -0800
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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.