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From: Bill Sloman <bill.sloman@ieee.org>
Newsgroups: sci.electronics.design
Subject: Re: Instead scopes
Date: Tue, 3 Sep 2024 15:30:13 +1000
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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.

>> 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.
>>
>> 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.

-- 
Bill Sloman, Sydney