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From: john larkin <jlarkin_highland_tech>
Newsgroups: sci.electronics.design
Subject: Re: Instead scopes
Date: Wed, 04 Sep 2024 07:50:11 -0700
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On Tue, 3 Sep 2024 15:30:13 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:

>On 3/09/2024 7:57 am, john larkin wrote:
>> On Mon, 2 Sep 2024 15:25:59 -0000 (UTC), Phil Hobbs
>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>> 
>>> Joe Gwinn <joegwinn@comcast.net> wrote:
>>>> On Sun, 01 Sep 2024 19:49:39 -0700, john larkin
>>>> <jlarkin_highland_tech> wrote:
>>>>
>>>>> On Sun, 01 Sep 2024 17:43:32 -0400, Joe Gwinn <joegwinn@comcast.net>
>>>>> wrote:
>>>>>
>>>>>> On Sun, 01 Sep 2024 13:17:03 -0700, john larkin
>>>>>> <jlarkin_highland_tech> wrote:
>>>>>>
>>>>>>> On Sun, 01 Sep 2024 15:53:46 -0400, Joe Gwinn <joegwinn@comcast.net>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> On Sun, 1 Sep 2024 17:55:58 -0000 (UTC), Phil Hobbs
>>>>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>>>>>>>
>>>>>>>>> john larkin <jlarkin_highland_tech> wrote:
>>>>>>>>>> On Sun, 1 Sep 2024 17:45:46 +1000, Bill Sloman <bill.sloman@ieee.org>
>>>>>>>>>> wrote:
>>>>>>>>>>
>>>>>>>>>>> On 30/08/2024 2:21 am, Jan Panteltje wrote:
>>>>>>>>>>>> On a sunny day (Fri, 30 Aug 2024 00:43:39 +1000) it happened Bill Sloman
>>>>>>>>>>>> <bill.sloman@ieee.org> wrote in <vaq1f2$jdj$1@dont-email.me>:
>>>>>>>>>>>>
>>>>>>>>>>>>> It's lot easier and quicker to bread-board a circuit in LTSpice than it
>>>>>>>>>>>>> is to wire up a test circuit, but what that means is that you need to
>>>>>>>>>>>>> make fewer real circuits and they are a lot more likely to work when tested.
>>>>>>>>>>>>>
>>>>>>>>>>>>> That, on it's own, is enough to explain why labs look different today
>>>>>>>>>>>>> than they did in the dark ages.
>>>>>>>>>>>>
>>>>>>>>>>>> All it explains is boeings falling apart and astronuts ending up stuck at the ISS
>>>>>>>>>>>> and no moonlanding from the US, not even a probe.
>>>>>>>>>>>> Slimulations are _not_ realty and never will be.
>>>>>>>>>>>
>>>>>>>>>>> But they can capture useful parts of reality, if you know what you are
>>>>>>>>>>> doing.
>>>>>>>>>>>
>>>>>>>>>>> John Larkin's simulated inductors tend not to have any parallel capacitance.
>>>>>>>>>>
>>>>>>>>>> The trick is to know when it matters. ESR and core loss are usually
>>>>>>>>>> more important.
>>>>>>>>>>
>>>>>>>>>> I designed this surface-mount inductor for my Pockels Cell driver,
>>>>>>>>>> after several tries using commercial parts. They all smoked.
>>>>>>>>>>
>>>>>>>>>> It's wound on a specially marked Sharpie pen that we have carefully
>>>>>>>>>> reserved.
>>>>>>>>>
>>>>>>>>> It better have a regular calibration schedule, or your semiconductor
>>>>>>>>> customers may give you the raised eyebrow.
>>>>>>>>
>>>>>>>> Hmm.  To be overly serious:  With traceability to NIST (US) or NPL
>>>>>>>> (UK) or the like.
>>>>>>>>
>>>>>>>> The trend in standards is to eliminate standards tied to a physical
>>>>>>>> object.
>>>>>>>>
>>>>>>>> I have a Sharpie in hand.  The barrel that is not covered by the cap
>>>>>>>> is a truncated cone, being 11.0 mm at the blunt end and 12.32 mm near
>>>>>>>> the cap, 73 mm away.
>>>>>>>
>>>>>>> Mine is pretty cylindrical for the length of the coil. I expect that
>>>>>>> the operator's (ie, my)  applied tension affects the radius too.
>>>>>>
>>>>>> Most likely.
>>>>>>
>>>>>>
>>>>>>> That inductor sees 25 amps p-p, roughly a sawtooth, at 4 MHz. The
>>>>>>> Coilcraft parts that I tried all smoked, I guess from skin effect and
>>>>>>> proximity effect.
>>>>>>>
>>>>>>>>
>>>>>>>> Actually, all that's needed is to specify an ideal geometric shape,
>>>>>>>> with tolerances, in the formal documentation.
>>>>>>>>
>>>>>>>> Joe Gwinn
>>>>>>>
>>>>>>> I'll have someone start on a SolidWorks model.
>>>>>>
>>>>>> I bet you need the standoff, so the lossy FR4 material isn't too
>>>>>> close.  That should be in the requirements as well.
>>>>>
>>>>> The turns squish down into the gap-pad gunk, which is an OK heat
>>>>> conductor. The PCB under the pad is a big copper pour, top and bottom,
>>>>> with a zillion thermal vias.  There's more gap-pad on the underside of
>>>>> the board to dump heat into the baseplate.
>>>>>
>>>>> At 4 MHz, skin depth is 32 microns, so most of the copper is wasted.
>>>>> That's why it gets so hot.
>>>>>
>>>>> I tried three of the Coilcraft 1010VS parts in series, but they
>>>>> smoked, probably skin+proximity effect.  Maybe parallel would have
>>>>> been better.
>>>>>
>>>>>>
>>>>>> I'd specify the coil dimensions, not the mandrel dimensions, which may
>>>>>> be provided as a helpful suggestion only.
>>>>>>
>>>>>> Joe Gwinn
>>>>>
>>>>> I could have a mandrel machined or 3D printed, to more accurately wind
>>>>> the inductor. The improvement would be mostly cosmetic.
>>>>
>>>> Or choose a 12mm OD mandrel, and adjust elsewhere.  The advantage of
>>>> 12mm is that it's a common size. so just buy the rod and use it.
>>>>
>>>> .<https://www.mcmaster.com/products/shafts/shafts-2~/rotary-shafts-5/diameter~12-mm/>
>>>>
>>>> Actually, the requirement is a certain inductance while handling a
>>>> 4-MHz sawtooth at 25 Amps (p-p), so the frequency band is roughly 4 to
>>>> 20 MHz, to cover the first five harmonics  Which harmonic causes the
>>>> most heating?
>>>>
>>>> The dimensions et al are the construction details needed for Highland
>>>> to be able to replicate the part without your help.
>>>>
>>> Lo these forty year gone, I had this RF gig that involved making a lot of
>>> VHF LC oscillatior and filter protos.
>> 
>> I still design LC oscillators!
>
>You may put them together, but it sounds as if you evolve them rather 
>than design them. And you'd have your own coil-winding gear if you did 
>much of it. As Phil did.

Design, simulate, build, test, evolve. That's how engineering usually
works. At the bleeding edge of performance, unpredictable higher-order
effects happen. Sometimes whacking the competition depends on
understanding and taming those effects. That's more fun to me than
pushing a bunch of equations around.


>
>>> We had a hand-cranked coil winder that had a good selection of cylindrical
>>> steel mandrels with helical grooves to guide the wire, plus three or four
>>> sheets with tables of measured values for single-layer coils of various
>>> lengths.  With a couple of training runs, one learned how hard to pull on
>>> the wire so that it would just spring free from the mandrel.

My Sharpie is a nice red marker when it's not winding coils.

>>>
>>> That made it easy to make nice looking, high-Q coils for the inductance
>>> range of interest.  Good Medicine.
>
>At George Kent in Luton (1973-76) I got to wind my own small-signal 
>transformers. At Cambridge Instruments (1982-1991) I had to ask the 
>coil-winders on the shop floor to do it for me.

I used to have toroid winding machine. That's not actually a rational
thing to do.