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 -- 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
Modern replacement for feedthrough caps?
Started by ●July 7, 2021
Reply by ●July 7, 20212021-07-07
On Wed, 7 Jul 2021 11:11:58 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> 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 HobbsI hate those RF boxes with feedthrus. You have to solder wires to them, on odd surfaces of the boxes. Soldering to the can and then jumpering to the board is klutzy too. A connector on the PCB, with some filtering parts, should usually be enough. And there are filtered D-subs too. An RJ45, with or without the magnetics, could be a well shielded power or slow-signal connector too. PoE version maybe. They shield well to a cutout in a box without being captive. Cheap. -- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
Reply by ●July 7, 20212021-07-07
jlarkin@highlandsniptechnology.com wrote:> On Wed, 7 Jul 2021 11:11:58 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> 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 hate those RF boxes with feedthrus. You have to solder wires to > them, on odd surfaces of the boxes. Soldering to the can and then > jumpering to the board is klutzy too. > > A connector on the PCB, with some filtering parts, should usually be > enough. And there are filtered D-subs too. > > An RJ45, with or without the magnetics, could be a well shielded power > or slow-signal connector too. PoE version maybe. They shield well to a > cutout in a box without being captive. Cheap.This is actually a little steel box with two switchers inside, that goes into one of our POC gizmos. I want to make it a little more product-friendly. I'll look at the RJ45s, thanks. 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 7, 20212021-07-07
On Wed, 7 Jul 2021 12:50:11 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>jlarkin@highlandsniptechnology.com wrote: >> On Wed, 7 Jul 2021 11:11:58 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> 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 hate those RF boxes with feedthrus. You have to solder wires to >> them, on odd surfaces of the boxes. Soldering to the can and then >> jumpering to the board is klutzy too. >> >> A connector on the PCB, with some filtering parts, should usually be >> enough. And there are filtered D-subs too. >> >> An RJ45, with or without the magnetics, could be a well shielded power >> or slow-signal connector too. PoE version maybe. They shield well to a >> cutout in a box without being captive. Cheap. > >This is actually a little steel box with two switchers inside, that goes >into one of our POC gizmos. I want to make it a little more >product-friendly. > >I'll look at the RJ45s, thanks. > >Cheers > >Phil HobbsThere are some affordable filtered D9 connectors too. On the outside, use a ribbon cable mate, optionally with a clip-on ferrite for super shielding. Steel is good. We've had nasty mag field leaks from little potted dc-dc converters. Surface-mount inductors can spray fields everywhere. But a surface-mount RJ45 is a pretty good option. -- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
Reply by ●July 7, 20212021-07-07
jlarkin@highlandsniptechnology.com wrote:> On Wed, 7 Jul 2021 12:50:11 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> jlarkin@highlandsniptechnology.com wrote: >>> On Wed, 7 Jul 2021 11:11:58 -0400, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> 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 hate those RF boxes with feedthrus. You have to solder wires to >>> them, on odd surfaces of the boxes. Soldering to the can and then >>> jumpering to the board is klutzy too. >>> >>> A connector on the PCB, with some filtering parts, should usually be >>> enough. And there are filtered D-subs too. >>> >>> An RJ45, with or without the magnetics, could be a well shielded power >>> or slow-signal connector too. PoE version maybe. They shield well to a >>> cutout in a box without being captive. Cheap. >> >> This is actually a little steel box with two switchers inside, that goes >> into one of our POC gizmos. I want to make it a little more >> product-friendly. >> >> I'll look at the RJ45s, thanks. > > There are some affordable filtered D9 connectors too. On the outside, > use a ribbon cable mate, optionally with a clip-on ferrite for super > shielding. > > Steel is good. We've had nasty mag field leaks from little potted > dc-dc converters. Surface-mount inductors can spray fields everywhere.I got a bunch of nickel-plated steel tins (the size and shape of the smaller Altoids package) off AliExpress. The lids slide on and off rather than having hinges, so the contact is better, and a few drops of solder improves matters further. With LC filters inside the box and feedthrough caps to the outside, you'd never know what was in there--my patent-pending shielded coax loop doesn't pick up anything.> > But a surface-mount RJ45 is a pretty good option.Thanks! 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 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.
Reply by ●July 8, 20212021-07-08
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 -- 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.Or bolt it on. I was thinking about a stick-on kapton thing, that was an EMI filter feedthru. Or a small standard PCB that has a barrel connector for power, and an emi filter. And an LED. Bolt that into the bottom of an Altoids can. But I don't like Altoids. https://www.dropbox.com/s/gj54oa19b2w5b0h/Z496_Can.jpg?raw=1 https://www.dropbox.com/s/cuxn5r7yzenb8m2/Z496_Out.jpg?raw=1 -- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
Reply by ●July 8, 20212021-07-08
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 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 HobbsWe finally got sick of the dreadful Hammond boxes, so we did our own extrusions. https://www.dropbox.com/s/yf1ykiialxgaad7/J736_Box_1.jpg?raw=1 https://www.dropbox.com/s/q5y5953fmar00lx/J744_2.jpg?raw=1 We buy it blue anodized and laser the graphics... no stickers either. We have a bigger one too.
