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.
Modern replacement for feedthrough caps?
Started by ●July 7, 2021
Reply by ●July 8, 20212021-07-08
Reply by ●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.net http://hobbs-eo.com
Reply by ●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 HobbsThe 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 ●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.net http://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 HobbsFor 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 ●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.net http://hobbs-eo.com
Reply by ●July 9, 20212021-07-09
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 HobbsSeriously! 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.
