On Fri, 9 Jul 2021 11:29:08 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
>jlarkin@highlandsniptechnology.com wrote:
>> On Fri, 9 Jul 2021 07:48:08 -0400, Phil Hobbs
>> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>>
>>> Rhydian wrote:
>>>> On Wed, 07 Jul 2021 11:11:58 -0400, Phil Hobbs wrote:
>>>>
>>>>> Hi, all,
>>>>>
>>>>> Some years back, in one of my more inspired moments, I bought a lifetime
>>>>> supply of 1.5 nF Soviet feedthrough capacitors from eBay. I have about
>>>>> 1,500 of them left, which should be good for building protos till about
>>>>> 2175 AD.
>>>>>
>>>>> Feedthroughs are great because they let you get supply and control
>>>>> wiring in and out of RF shields without trashing the shield
>>>>> effectiveness. They solder into a hole in the can, so whatever RF gets
>>>>> onto the wire, gets shunted to ground before leaving the shield. Magic.
>>>>>
>>>>> There are two problems, though: (i) they require hand wiring, and (ii)
>>>>> they now cost $15 each!
>>>>>
>>>>> SMT devices that claim to be feedthrough caps exist, but on their face
>>>>> they don't solve the wire pickup/re-radiation problem.
>>>>>
>>>>> Thoughts?
>>>>>
>>>>> Cheers
>>>>>
>>>>> Phil Hobbs
>>>>
>>>> The SMT equivalents I have seen are (e.g.) Murata's NFL series of 3-
>>>> terminal caps. The idea is that the centre pin straddles a trace on your
>>>> board, with multiple vias to the ground plane, and the shield can is
>>>> soldered to this trace, with a mouse-bite to go over the body of the SMT
>>>> part.
>>>>
>>>> Cross section looks a bit like this:
>>>>
>>>> -------------+
>>>> |
>>>> SHIELD |
>>>> |
>>>> ______
>>>> [_ __ _]
>>>> Top ------- -- ----------
>>>> ][
>>>> GND =======================
>>>>
>>>>
>>>> It's never going to be as effective as a traditional leaded feed-through,
>>>> as you lose the 360 shield connection and the RF currents in the shield
>>>> are not symmetrically distributed. I've never seen this quantified,
>>>> though.
>>>>
>>>> The part we used was NFL21SP106X1C3D. But the design (long since
>>>> retired) was from 20 years ago when we had no RF test equipment and not
>>>> much understanding of EMI issues. It would be interesting to go back and
>>>> run some proper tests on them.
>>>>
>>>>
>>>
>>> Thanks. That's OK for electrostatic shielding, but won't fix the
>>> magnetic problem because there's no simple way to get the steel to be
>>> continuous. I guess one could stick little PCB tabs through the shield
>>> as long as it was on only one side of the board.
>>>
>>> Cheers
>>>
>>> Phil Hobbs
>>
>> For serious magnetic shielding you need a seamless hi-mu enclosure and
>> ship-in-a-bottle construction techniques.
>>
>>
>>
>Or else a long extension cord. ;)
>
>Cheers
>
>Phil Hobbs
Seriously! Magnetic shielding is really hard, especially at low, like
60 Hz frequencies. Something like a Hoffmann steel utility box is
basically transparent.
--
John Larkin Highland Technology, Inc
The best designs are necessarily accidental.
Reply by Phil Hobbs●July 9, 20212021-07-09
jlarkin@highlandsniptechnology.com wrote:
> On Fri, 9 Jul 2021 07:48:08 -0400, Phil Hobbs
> <pcdhSpamMeSenseless@electrooptical.net> wrote:
>
>> Rhydian wrote:
>>> On Wed, 07 Jul 2021 11:11:58 -0400, Phil Hobbs wrote:
>>>
>>>> Hi, all,
>>>>
>>>> Some years back, in one of my more inspired moments, I bought a lifetime
>>>> supply of 1.5 nF Soviet feedthrough capacitors from eBay. I have about
>>>> 1,500 of them left, which should be good for building protos till about
>>>> 2175 AD.
>>>>
>>>> Feedthroughs are great because they let you get supply and control
>>>> wiring in and out of RF shields without trashing the shield
>>>> effectiveness. They solder into a hole in the can, so whatever RF gets
>>>> onto the wire, gets shunted to ground before leaving the shield. Magic.
>>>>
>>>> There are two problems, though: (i) they require hand wiring, and (ii)
>>>> they now cost $15 each!
>>>>
>>>> SMT devices that claim to be feedthrough caps exist, but on their face
>>>> they don't solve the wire pickup/re-radiation problem.
>>>>
>>>> Thoughts?
>>>>
>>>> Cheers
>>>>
>>>> Phil Hobbs
>>>
>>> The SMT equivalents I have seen are (e.g.) Murata's NFL series of 3-
>>> terminal caps. The idea is that the centre pin straddles a trace on your
>>> board, with multiple vias to the ground plane, and the shield can is
>>> soldered to this trace, with a mouse-bite to go over the body of the SMT
>>> part.
>>>
>>> Cross section looks a bit like this:
>>>
>>> -------------+
>>> |
>>> SHIELD |
>>> |
>>> ______
>>> [_ __ _]
>>> Top ------- -- ----------
>>> ][
>>> GND =======================
>>>
>>>
>>> It's never going to be as effective as a traditional leaded feed-through,
>>> as you lose the 360 shield connection and the RF currents in the shield
>>> are not symmetrically distributed. I've never seen this quantified,
>>> though.
>>>
>>> The part we used was NFL21SP106X1C3D. But the design (long since
>>> retired) was from 20 years ago when we had no RF test equipment and not
>>> much understanding of EMI issues. It would be interesting to go back and
>>> run some proper tests on them.
>>>
>>>
>>
>> Thanks. That's OK for electrostatic shielding, but won't fix the
>> magnetic problem because there's no simple way to get the steel to be
>> continuous. I guess one could stick little PCB tabs through the shield
>> as long as it was on only one side of the board.
>>
>> Cheers
>>
>> Phil Hobbs
>
> For serious magnetic shielding you need a seamless hi-mu enclosure and
> ship-in-a-bottle construction techniques.
>
>
>
Or else a long extension cord. ;)
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.nethttp://hobbs-eo.com
Reply by ●July 9, 20212021-07-09
On Fri, 9 Jul 2021 07:48:08 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
>Rhydian wrote:
>> On Wed, 07 Jul 2021 11:11:58 -0400, Phil Hobbs wrote:
>>
>>> Hi, all,
>>>
>>> Some years back, in one of my more inspired moments, I bought a lifetime
>>> supply of 1.5 nF Soviet feedthrough capacitors from eBay. I have about
>>> 1,500 of them left, which should be good for building protos till about
>>> 2175 AD.
>>>
>>> Feedthroughs are great because they let you get supply and control
>>> wiring in and out of RF shields without trashing the shield
>>> effectiveness. They solder into a hole in the can, so whatever RF gets
>>> onto the wire, gets shunted to ground before leaving the shield. Magic.
>>>
>>> There are two problems, though: (i) they require hand wiring, and (ii)
>>> they now cost $15 each!
>>>
>>> SMT devices that claim to be feedthrough caps exist, but on their face
>>> they don't solve the wire pickup/re-radiation problem.
>>>
>>> Thoughts?
>>>
>>> Cheers
>>>
>>> Phil Hobbs
>>
>> The SMT equivalents I have seen are (e.g.) Murata's NFL series of 3-
>> terminal caps. The idea is that the centre pin straddles a trace on your
>> board, with multiple vias to the ground plane, and the shield can is
>> soldered to this trace, with a mouse-bite to go over the body of the SMT
>> part.
>>
>> Cross section looks a bit like this:
>>
>> -------------+
>> |
>> SHIELD |
>> |
>> ______
>> [_ __ _]
>> Top ------- -- ----------
>> ][
>> GND =======================
>>
>>
>> It's never going to be as effective as a traditional leaded feed-through,
>> as you lose the 360 shield connection and the RF currents in the shield
>> are not symmetrically distributed. I've never seen this quantified,
>> though.
>>
>> The part we used was NFL21SP106X1C3D. But the design (long since
>> retired) was from 20 years ago when we had no RF test equipment and not
>> much understanding of EMI issues. It would be interesting to go back and
>> run some proper tests on them.
>>
>>
>
>Thanks. That's OK for electrostatic shielding, but won't fix the
>magnetic problem because there's no simple way to get the steel to be
>continuous. I guess one could stick little PCB tabs through the shield
>as long as it was on only one side of the board.
>
>Cheers
>
>Phil Hobbs
For serious magnetic shielding you need a seamless hi-mu enclosure and
ship-in-a-bottle construction techniques.
--
John Larkin Highland Technology, Inc
The best designs are necessarily accidental.
Reply by Phil Hobbs●July 9, 20212021-07-09
Rhydian wrote:
> On Wed, 07 Jul 2021 11:11:58 -0400, Phil Hobbs wrote:
>
>> Hi, all,
>>
>> Some years back, in one of my more inspired moments, I bought a lifetime
>> supply of 1.5 nF Soviet feedthrough capacitors from eBay. I have about
>> 1,500 of them left, which should be good for building protos till about
>> 2175 AD.
>>
>> Feedthroughs are great because they let you get supply and control
>> wiring in and out of RF shields without trashing the shield
>> effectiveness. They solder into a hole in the can, so whatever RF gets
>> onto the wire, gets shunted to ground before leaving the shield. Magic.
>>
>> There are two problems, though: (i) they require hand wiring, and (ii)
>> they now cost $15 each!
>>
>> SMT devices that claim to be feedthrough caps exist, but on their face
>> they don't solve the wire pickup/re-radiation problem.
>>
>> Thoughts?
>>
>> Cheers
>>
>> Phil Hobbs
>
> The SMT equivalents I have seen are (e.g.) Murata's NFL series of 3-
> terminal caps. The idea is that the centre pin straddles a trace on your
> board, with multiple vias to the ground plane, and the shield can is
> soldered to this trace, with a mouse-bite to go over the body of the SMT
> part.
>
> Cross section looks a bit like this:
>
> -------------+
> |
> SHIELD |
> |
> ______
> [_ __ _]
> Top ------- -- ----------
> ][
> GND =======================
>
>
> It's never going to be as effective as a traditional leaded feed-through,
> as you lose the 360 shield connection and the RF currents in the shield
> are not symmetrically distributed. I've never seen this quantified,
> though.
>
> The part we used was NFL21SP106X1C3D. But the design (long since
> retired) was from 20 years ago when we had no RF test equipment and not
> much understanding of EMI issues. It would be interesting to go back and
> run some proper tests on them.
>
>
Thanks. That's OK for electrostatic shielding, but won't fix the
magnetic problem because there's no simple way to get the steel to be
continuous. I guess one could stick little PCB tabs through the shield
as long as it was on only one side of the board.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.nethttp://hobbs-eo.com
Reply by Rhydian●July 9, 20212021-07-09
On Wed, 07 Jul 2021 11:11:58 -0400, Phil Hobbs wrote:
> Hi, all,
>
> Some years back, in one of my more inspired moments, I bought a lifetime
> supply of 1.5 nF Soviet feedthrough capacitors from eBay. I have about
> 1,500 of them left, which should be good for building protos till about
> 2175 AD.
>
> Feedthroughs are great because they let you get supply and control
> wiring in and out of RF shields without trashing the shield
> effectiveness. They solder into a hole in the can, so whatever RF gets
> onto the wire, gets shunted to ground before leaving the shield. Magic.
>
> There are two problems, though: (i) they require hand wiring, and (ii)
> they now cost $15 each!
>
> SMT devices that claim to be feedthrough caps exist, but on their face
> they don't solve the wire pickup/re-radiation problem.
>
> Thoughts?
>
> Cheers
>
> Phil Hobbs
The SMT equivalents I have seen are (e.g.) Murata's NFL series of 3-
terminal caps. The idea is that the centre pin straddles a trace on your
board, with multiple vias to the ground plane, and the shield can is
soldered to this trace, with a mouse-bite to go over the body of the SMT
part.
Cross section looks a bit like this:
-------------+
|
SHIELD |
|
______
[_ __ _]
Top ------- -- ----------
][
GND =======================
It's never going to be as effective as a traditional leaded feed-through,
as you lose the 360 shield connection and the RF currents in the shield
are not symmetrically distributed. I've never seen this quantified,
though.
The part we used was NFL21SP106X1C3D. But the design (long since
retired) was from 20 years ago when we had no RF test equipment and not
much understanding of EMI issues. It would be interesting to go back and
run some proper tests on them.
Reply by Phil Hobbs●July 8, 20212021-07-08
dcaster@krl.org wrote:
> On Wednesday, July 7, 2021 at 11:12:05 AM UTC-4, Phil Hobbs wrote:
>> Hi, all,
>>
>> Some years back, in one of my more inspired moments, I bought a lifetime
>> supply of 1.5 nF Soviet feedthrough capacitors from eBay. I have about
>> 1,500 of them left, which should be good for building protos till about
>> 2175 AD.
>>
>> Feedthroughs are great because they let you get supply and control
>> wiring in and out of RF shields without trashing the shield
>> effectiveness. They solder into a hole in the can, so whatever RF gets
>> onto the wire, gets shunted to ground before leaving the shield. Magic.
>>
>> There are two problems, though: (i) they require hand wiring, and (ii)
>> they now cost $15 each!
>>
>> SMT devices that claim to be feedthrough caps exist, but on their face
>> they don't solve the wire pickup/re-radiation problem.
>>
>> Thoughts?
>
> I would think one could get them made for a lot less than $15 each by someone with a screw machine. But that does not solve the hand wiring.
Maybe, if you could get somebody to make the high-k ceramic ferrules.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.nethttp://hobbs-eo.com
Reply by whit3rd●July 8, 20212021-07-08
On Thursday, July 8, 2021 at 9:04:07 AM UTC-7, dcaster@krl.org wrote:
> On Wednesday, July 7, 2021 at 11:12:05 AM UTC-4, Phil Hobbs wrote:
> > Hi, all,
> >
> > Some years back, in one of my more inspired moments, I bought a lifetime
> > supply of 1.5 nF Soviet feedthrough capacitors from eBay....
[and some feedthroughs are available still]
> > There are two problems, though: (i) they require hand wiring, and (ii)
> > they now cost $15 each!
> I would think one could get them made for a lot less than $15 each by someone with a screw machine. But that does not solve the hand wiring.
The screw machine folk still make, I hope, turret terminals which press into a PTFE collar,
which would work for a feedthrough. Similar to these
<https://www.mill-max.com/products/socket/380-xx-xxx-00-000800>
except the PTFE collar expands when the terminal is pressed in, so it locks into the hole.
There's no current supplier, though, for the cylindrical ceramic capacitors that were the
core of those old feedthroughs, and you can't turn those out on a screw machine.
Reply by John Larkin●July 8, 20212021-07-08
On Thu, 8 Jul 2021 10:28:16 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
>Chris Jones wrote:
>> On 08/07/2021 01:11, Phil Hobbs wrote:
>>> Hi, all,
>>>
>>> Some years back, in one of my more inspired moments, I bought a
>>> lifetime supply of 1.5 nF Soviet feedthrough capacitors from eBay.� I
>>> have about 1,500 of them left, which should be good for building
>>> protos till about 2175 AD.
>>>
>>> Feedthroughs are great because they let you get supply and control
>>> wiring in and out of RF shields without trashing the shield
>>> effectiveness.� They solder into a hole in the can, so whatever RF
>>> gets onto the wire, gets shunted to ground before leaving the shield.
>>> Magic.
>>>
>>> There are two problems, though: (i) they require hand wiring, and (ii)
>>> they now cost $15 each!
>>>
>>> SMT devices that claim to be feedthrough caps exist, but on their face
>>> they don't solve the wire pickup/re-radiation problem.
>>>
>>> Thoughts?
>>>
>>> Cheers
>>>
>>> Phil Hobbs
>>>
>>
>>
>> I have been thinking about this also.
>>
>> If you make a little PCB with a ground plane on one side, and put a
>> plated-through hole in the middle for a signal wire to pass through, not
>> connected to the ground plane, and put surface mount capacitors radially
>> between the through-hole and the ground plane, that would be a pretty
>> good approximation to the feedthrough capacitors that you bought.
>>
>> I used 4 capacitors in a + arrangement, you could use more if your
>> pick-and-place permits. You'd have to solder the groundplane of that
>> little PCB to the tinplate of the box around the hole you mount it on,
>> either by sweating the tinplate to the groundplane itself from the other
>> side of the tinplate, or with castellated pads on the edges of the PCB,
>> or by replacing one entire face of the tinplate box by the PCB with a
>> groundplane oriented outwards. I've made and used these, and they were
>> good enough for what I needed. It would be interesting to measure some
>> with a VNA.
>>
>> Obviously if your product's main PCB doesn't need parts on both sides,
>> you can integrate the feedthrough-replacement-PCBs with the main PCB,
>> reducing assembly costs.
>>
>> If you have a lot of layers, you could also add additional capacitance
>> inside the feedthrough PCB, by connecting the signal pad to a circle or
>> other shape on an inner layer adjacent to groundplane layers. Putting
>> multiple capacitors in parallel is not always an improvement of course,
>> if resonances occur, but with some testing it may be possible to improve
>> over whatever parasitic inductance the surface mount caps exhibit.
>
>Not a bad idea, thanks. If we can keep the hole in the tinplate small
>enough, it might be OK just with regular mounting screws--the
>featureless bottom-side ground should look after the electrostatic
>shielding, leaving the box to do the last bit of magnetic shielding.
>
>I'll try dremelling up an example and see.
>
>Cheers
>
>Phil Hobbs
On Wednesday, July 7, 2021 at 11:12:05 AM UTC-4, Phil Hobbs wrote:
> Hi, all,
>
> Some years back, in one of my more inspired moments, I bought a lifetime
> supply of 1.5 nF Soviet feedthrough capacitors from eBay. I have about
> 1,500 of them left, which should be good for building protos till about
> 2175 AD.
>
> Feedthroughs are great because they let you get supply and control
> wiring in and out of RF shields without trashing the shield
> effectiveness. They solder into a hole in the can, so whatever RF gets
> onto the wire, gets shunted to ground before leaving the shield. Magic.
>
> There are two problems, though: (i) they require hand wiring, and (ii)
> they now cost $15 each!
>
> SMT devices that claim to be feedthrough caps exist, but on their face
> they don't solve the wire pickup/re-radiation problem.
>
> Thoughts?
I would think one could get them made for a lot less than $15 each by someone with a screw machine. But that does not solve the hand wiring.
Dan
>
> Cheers
>
> Phil Hobbs
>
> --
> Dr Philip C D Hobbs
> Principal Consultant
> ElectroOptical Innovations LLC / Hobbs ElectroOptics
> Optics, Electro-optics, Photonics, Analog Electronics
> Briarcliff Manor NY 10510
>
> http://electrooptical.net
> http://hobbs-eo.com
Reply by ●July 8, 20212021-07-08
On Thu, 8 Jul 2021 23:58:11 +1000, Chris Jones
<lugnut808@spam.yahoo.com> wrote:
>On 08/07/2021 01:11, Phil Hobbs wrote:
>> Hi, all,
>>
>> Some years back, in one of my more inspired moments, I bought a lifetime
>> supply of 1.5 nF Soviet feedthrough capacitors from eBay.� I have about
>> 1,500 of them left, which should be good for building protos till about
>> 2175 AD.
>>
>> Feedthroughs are great because they let you get supply and control
>> wiring in and out of RF shields without trashing the shield
>> effectiveness.� They solder into a hole in the can, so whatever RF gets
>> onto the wire, gets shunted to ground before leaving the shield.� Magic.
>>
>> There are two problems, though: (i) they require hand wiring, and (ii)
>> they now cost $15 each!
>>
>> SMT devices that claim to be feedthrough caps exist, but on their face
>> they don't solve the wire pickup/re-radiation problem.
>>
>> Thoughts?
>>
>> Cheers
>>
>> Phil Hobbs
>>
>
>
>I have been thinking about this also.
>
>If you make a little PCB with a ground plane on one side, and put a
>plated-through hole in the middle for a signal wire to pass through, not
>connected to the ground plane, and put surface mount capacitors radially
>between the through-hole and the ground plane, that would be a pretty
>good approximation to the feedthrough capacitors that you bought.
>
>I used 4 capacitors in a + arrangement, you could use more if your
>pick-and-place permits. You'd have to solder the groundplane of that
>little PCB to the tinplate of the box around the hole you mount it on,
>either by sweating the tinplate to the groundplane itself from the other
>side of the tinplate, or with castellated pads on the edges of the PCB,
>or by replacing one entire face of the tinplate box by the PCB with a
>groundplane oriented outwards. I've made and used these, and they were
>good enough for what I needed. It would be interesting to measure some
>with a VNA.