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From: john larkin <jlarkin_highland_tech>
Newsgroups: sci.electronics.design
Subject: Re: Instead scopes
Date: Mon, 02 Sep 2024 14:57:39 -0700
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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!

>
>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. 
>
>Cheers 
>
>Phil Hobbs 

Coilcraft makes a bunch of bare-naked RF inductors.

We like this encapsulated part:

https://www.coilcraft.com/en-us/products/rf/air-core-inductors/midi-spring/1812sms/?skuId=26054|26274

What's surprising is that the "natural" tempco of a copper solenoid
inductor runs around +120 ppm/degC, but this one is around +40. The
plastic must compensate for the copper somehow.