how do you design RF cans? - Page 1
Forum section: electronics / rf-microwave

author: CopperCone
author_rank: Super Contributor
timestamp: June 13, 2018, 01:14:55 am
content: I noticed if you take apart a high quality RF cans you have little tunnels basically, but I have seen on UHF stuff (say to 3GHz) they just whack a circuit board in a can that does not really have complicated internal geometry, it is just a well sealing aluminum box.I have seen some designs where you basically have the signal path, and then the can fits over it with like a 1cm lotus , so you basically have little 'caves' or tunnels separating everything out, so its almost like some kind of coaxial shield. The top and bottom walls of the can are mated through the non edge areas of the circuit boards with heavy (isolated?) via stiching.. or are they nonisolated?Also, how important are curves on the internal geometry?Lets say I wanted to make this, but using steel sheet and welding, for the sake of not needing to use big milling machines (hassle to own), just welded nicely and maybe ground down a bit (not to that extent) with a die grinder and sanded. I guess you can really fill the shit out of the welds to make your own bevels with a die grinder, but is it really necessary?http://www.gquipment.com/30-large_default/rf-enclosure-mini-aluminium.jpgSo I would not have the interior bevels.Is this stuff done in a simulator? Or are there pretty good rules of thumb with frequency?I just can't see myself owning something that can mill something like a 12x12 inch RF can.I figure you can get a decent flat seal by puttin the thing in a fucking wood planer so long you set it for very tiny cuts, then finish it off lapping on some sand paper ontop of a big granite measuring block... otherwise you still need a damn mill to flycut itand if its very uneven you can use bluing and an aluminum file to get it within a few thousanths (fairly easy so long you use a proper aluminum file), so it does not try to fly out of the planer and kill you, to account from distortion due to weldingmuch more fun to build then milling too. unless you have a CNC then you can just chill while you wait but I probobly wont be able to afford that kind of shit for a decadeI assume you can get a good enough surface finish by going over it with a few different grits of sand paper (maybe to 1000) and then polishing it with some roguethen you can anodize it so it looks cool and laser ingrave or etch it and all sorts of stuff with the price of some kind of mill, plus you have welding equipment and developed shop skills for all your antenna, optics mounts and shit

author: David Hess
author_rank: Super Contributor
timestamp: June 13, 2018, 04:10:16 am
content: Larger cavity volumes have a lower waveguide cutoff frequency allowing more coupling between circuits. Sometimes an absorber is added rather than messing with the shield geometry.

author: Dubbie
author_rank: Unknown
timestamp: June 13, 2018, 06:07:31 am
content: Good luck getting any of the precision you are talking about with hand tools.You're better off getting an old manual mill.

author: bd139
author_rank: Super Contributor
timestamp: June 13, 2018, 09:54:21 am
content: Not even worth it for one offs. Look at S53MV for construction ideas. Several GHz are fine with mediocre enclosures:http://lea.hamradio.si/~s53mv/spectana/sa.htmlThe milled parts are ridiculously expensive. They cost more than the boards that went in them when I did assembly on them.

author: Yansi
author_rank: Super Contributor
timestamp: June 13, 2018, 11:04:22 am
content: Unfortunately I can not agree completely.I have just asked a few (CNC) local machine shops, if they would mill for me a small custom RF enclosure. The prices quoted were not exactly cheap, but affordable. Also, the price goes down the more of them you order. Most of the price takes the setup (CNC programming).At five pieces of small custom 60x40x12mm I was quoted $68. As I've said: Not cheap, but affordable.So if you take time do design yourself some universal sizes you will use often, then I guess that may be affordable way to have professional looking enclosures.Mind you, I have access to some decent machinery and metal stock. I could mill some of these myself, not a big deal. But if you count the time it will take you to make one (just cutting stock and squaring it on the mill), you will find that you already spent the amount of time equal to the price the CNC guys offered for 5 pieces.Note I have nothing against the "mediocre enclosures". I use them often for prototypes. A sheet of tinned steel cost just pennies. But when I get to the point making something nice and permanent, I think, that milled aluminium cases are just affordable.

author: CopperCone
author_rank: Super Contributor
timestamp: June 13, 2018, 02:03:12 pm
content: Tollerances matter with these things? They should be accurate to 0.3mm or so if dilligent i thinkBtw for making flats you can make really flat shit by hand using a scraper or file and a granite block and blueing.

author: CopperCone
author_rank: Super Contributor
timestamp: June 13, 2018, 04:07:27 pm
content: Also doesent waveguide have a low and high frequency cutoff for the efficent mode of propogation, so it acts likea bandpass filter with impedance?Well more of a high pass filter, then some kind of notchyness/moding past its design frequency. I am actually looking ats parameter wideband testsof waveguide to see whats going onI thought it was not really critical so long its sealed properlysince it does not really follow the pcb traces like a stripline or coax would, so what difference does it make if the wall developed a .5 degree bend due to weld stresses or a bevel is not exact?The most important part is the top and bottom plates being parallel right.. But the waveguide behavior is hard for me to understand.I know that in classical waveguide you needa certain geometry for the right TE modes. But since the edges in most cans are beveled dont you get some kinda half circular have rectangular shit that has complicated propagation modes? When i cut apart real waveguide it is really square inside, it looks extruded or cast squareI also renember thatin my microwave antenna for 20ghz it uses some kinda oval waveguide which kinda fits but you really need a transition to a square endlauncherI need to look at lance or wheelers? Book it had some information i think about te modes of some random geometries but thats proper waveguide, this seems likea bootleg waveguide with a really bootleg launcher (pcb).. But you want it not to couple so youdont lose signal power so like you gottathink backwords or somethingSo given that the traces are allover the place, and youdont have a real injector on the pcb does a slightly angled wall matter? Do i really need todeal with paying someone to run a robot orto get a three car garage to do this? I dont like paying any kind of contractors or tradesmen really...Also, ineed to look for waveguide tollerances for manufactured waveguide i am curious nowAnd i am trying to get my money from my android phone back so thats why these daytime posts are a bit shoddy, enjoying the outdoors and people watching etc.. 400 dollars 3 years ago and i was hardly using it..

author: Wolfgang
author_rank: Super Contributor
timestamp: August 15, 2018, 08:55:12 pm
content: Same experience:- Milled enclosures are perfect, but only when properly plated and when the lids are screwed on with a LOT of screws.- Up to a few GHz, tinplate boxes work with a little higher loss, but good enough for a lot of applications (yes, the 0.05dB NF amplifier is NOT one of them).- Make the enclosures as small and flat as you can to avoid resonances, or at least to shift them up to a very high frequency where your circuitry has no gain left.- Use chambers and absorptive material to dampen out resonances.Much success !

author: coppercone2
author_rank: Super Contributor
timestamp: August 19, 2018, 05:06:50 pm
content: What do you mean by properly plated?Also what do you think about RF gaskets like BeCu fingers or foam rather then super tight mechanical design using many screws? Especially if they are glued onto a oxide clean surface using conductive epoxy rather then the shitty adhesive they are supplied with. Can you get away from having to use a flycutter and stuff on a home made box this way so it closes properly? I can file flat a alumium box real nice but it won't ave the quality of a flycutter.I assume you mean that a slot antenna forms between the screws so you need alot of them to break up the little loop that forms right? How do finely spaced RF fingers compare to a typical machine screw heavy enclosure, if proper tension is achieved? How about multiple rows of fingers, with overlapping (so there is no slots), or fingers in combination with compressible foam? Can generalizations be made to the gap geometry to get similar performance from tight machining and creative solutions like fingers?https://www.compeng.com.au/rf-shielded-enclosures-accessories/And what if you just solder the can shut and rely on a special heating device to open it, using low temp high conductivity solder? Easy enough to make a custom fitted hot wire heater for a specific can. Or conductive epoxy seals?I am trying to find ways around owning large, heavy, dirty and space hungry machine tools that I have little use for or interest in. And the tooling costs are absurd. And I don't want to learn all the settings, feed rates, etc.It is difficult for me to compare though, because I would need the milled enclosure to compare my home made ideas to.Also, what are chambers?

author: David Hess
author_rank: Super Contributor
timestamp: August 19, 2018, 05:56:27 pm
content: Quote from: coppercone2 on August 19, 2018, 05:06:50 pmThere is another kind of gasket material which is springy and has sharp "fingers" on both sides to puncture any insulating surface like a star washer. I have also seen copper braid used.QuoteExactly and it happens with pretty much any material. Springy materials like steel may have the fingers built in. Anything which forms an insulating oxide surface like aluminum is especially a problem.QuoteI have seen this with tin plated steel shields and hermetically sealed enclosures.

author: Ian.M
author_rank: Super Contributor
timestamp: August 19, 2018, 06:20:26 pm
content: For rectangular one-offs, if you don't have a box & pan brake with small enough fingers to form then out of tin plated steel, just use double sided coper clad FR4. Solder the inside seams, and copper foil tape the outside seams. Either make up L section fingered strips to seat it on from springy brass shim stock and solder them down, or solder it directly to the PCB, or solder on brass angle flanges and bolt it down on a tinned copper braid gasket.

author: coppercone2
author_rank: Super Contributor
timestamp: August 19, 2018, 06:36:46 pm
content: How do all these methods compare to the industrial RF standard of using a milled machine box that is surface ground and sealed with screws every 1.5cm or so? Does anyone have any plots that show attenuation?

author: mzzj
author_rank: Super Contributor
timestamp: August 19, 2018, 06:46:03 pm
content: If you are just making enclosures and rf "boxes" they don't need be accurate, just tight seams and lid with enough many screws. Corner rounding radius or wall paralleism doesn't matter.If you start making parts where the "box" is not just a box (like cavity filters) then things get more "interesting"

author: coppercone2
author_rank: Super Contributor
timestamp: August 19, 2018, 06:54:38 pm
content: Yes, I am interested in things that enclose PCB's, when I took apart some waveguide stuff it looks like you needed a deep shaper machine and a lathe to make the square sides and disks, not to mention various plating technology to make the silver plate on the aluminum waveguide. This was just a cavity filter thing.It does make me wonder if you can make waveguide out of welded stuff so long you have a very precise X-Y table on a very stable arbor press to use as a shaper, you can technically shave down the sides to parallelism, if you have a special tool that has scrapes on all 4 sides. It would be a lot of plunge cutting, I don't think a regular arbor press would be suited though. If you used thicker copper and solder instead of weld or braze it might not deform too much, so you might just need to shave a few hairs off, if you solder with spaces in place to ensure a consistent gap geometry, with minimum spacing between the parts (0.5thousanths maybe), since mechanical strength is irrelevant. It would be a nice machine if it can work because the travel would need to be like what, 3 inches?, and it would fit the same form as a drill press, so it would not occupy much floor space. It would only be hard if you need to make a big ass wave guide for like <2GHz. The tool would need to be long for for shaving copper or aluminum I doubt it would need to be very stiff? I imaging strait waveguide parts up to like 1.5 feet could be made that way, but hell if I know how to smooth out the interior of bends and stuff, maybe you could live with some irregularity thereThe stuff-in-waveguide looks like you need a serious machine and chemistry shop. I do have a feeling from reading that so long you are under like 15GHz you can get away with significant butchery of waveguide geometry with little consequencemicrowave101.com"During the brazing and hardening process the walls of the waveguide can become deformed from their ideal geometry. At frequencies Ku-band and lower this tends to not be much of a problem;a few mils of error represent less than 1% error and do not cause an appreciable effect on the insertion and phase of the signal at these frequencies.However, when reaching higher frequencies such a Ka, V, and definitely W, this becomes a problem worth thinking about when considering dip-brazing."Taking some liberties with his numbers, I figure a rule of thumb might be 0.005 inches bulk geometric change = 1% error, since a few probably means 3 and 3 is less then 1 so we can make 1 = 5. Engineering math. Might be as high as 0.01 inches.I have some avionics waveguide for around the Ku band, I wish I had a CMM to see what was considered acceptable for its manufacture. I doubt a micrometer will give me terribly useful information but I will give it a whirl. 5 thousandths is not that crazy accurate. Low melting point soft solders might make this really achievable. 1% of a high power signal is like 1dB. For 10GHz thats in the same ballpark as RG141, which is like 0.6dB/Foot @ 10GHz, wheras commercial WR90 waveguide is expected to have something like 0.03dB/foot. I wonder what he means exactly. If he means error from the ideal target specification, then we are golden, since 1% of 0.03dB is basically nothing. Who gives a shit if its 0.03dB +- 1% ?? Its still a dead short compared to anything else you can do. I doubt anyone here can even measure better then 0.05dB @ 10GHz anyway, unless they work for Lecroy or Agilent.I think I have seen hybrid cavity filter/PCB enclosure thing inside of a spectrum analyzer, but I never took apart the cavity filter bit, It's the part where you use screws to adjust little 'pistons' to tune the thing right?

author: David Hess
author_rank: Super Contributor
timestamp: August 19, 2018, 07:27:01 pm
content: Quote from: Ian.M on August 19, 2018, 06:20:26 pmI made my first FR4 boxes that way but they much stronger if the outside edges overlap so they can be soldered as well. This can also physically protect anything protruding through the FR4 like piston trimmers and feedthroughs as shown below.

author: coppercone2
author_rank: Super Contributor
timestamp: August 19, 2018, 07:30:03 pm
content: All I can complain about is that it needed some lacquer after soldering, like a coating of canned polyurathane spray, shellac, etc. And rubber feet.

author: bd139
author_rank: Super Contributor
timestamp: August 19, 2018, 07:32:19 pm
content: Lacquer just slows it down. Doesn’t solve the problem. Been there, found that out. Tinning the parts is probably better.Edit: or just shrug. Function over form

author: coppercone2
author_rank: Super Contributor
timestamp: August 19, 2018, 07:34:54 pm
content: how about top-coat clear-coat spray paint that uses acrylates? Lol, or just paint.I wonder if you can solder together waveguide out of FR4 thats decent if you coat the inside of the waveguide to prevent solder wicking, to minimize the multimode rounding that would occur from the solder wick. Like expose your PCB to have solder resist everywhere, then just wash it out with a solvent after soldering. You can glue it down first carefully with cyanoacrylate to provide the mechanical strength wich would ordinarily come from the large solder bevel when making a PCB box. Since less solder is used, there should be less deformative stresses, since the solder is being used for an electrical connection only. If you mate them well with glue, and have resists, you might just be able to lay down a bead of 0.2mm solder to make the joint at the seam. You would just need to very carefully glue it, using a microapplicator, and align everything correct. I wonder how much error that would result in, and the minimum amount of solder you can use to make a seamless electrical connection with minimum bevel to maintain the right angle as much as possible. I would angle the thing so the angle is pointing directly dowards, the thin solder wire is pressed into the fluxed bevel, with minimum copper exposure, and heat it with hot air or maybe pulsed laser?If 0.2mm of solder is pressed into a right angle, the bevel should be like 0.005 inches radius if the idea works.Maybe you can do even smaller if you figure out how to properly apply the fine grade solder paste. The most aggressive flux can be used since it would be cleaned afterwards.

author: bd139
author_rank: Super Contributor
timestamp: August 19, 2018, 07:41:55 pm
content: Paint works:https://aa7ee.wordpress.com/2013/10/19/the-vk3ye-micro-40-dsb-transceiver/Here's one I did recently, a simple return loss bridge. Didn't need to be terribly RF tight as it's HF only so the lid is just screwed on and it's single sided board so all the skanky copper stays on the inside:Edit: guts:

author: David Hess
author_rank: Super Contributor
timestamp: August 19, 2018, 08:03:35 pm
content: I used to clean and spray them in the past but the spray coating always rubs off and I think that makes it look worse than if it was just plain tarnished copper. That particular one is a helical resonator (1) so silver plating it would have some performance benefit (2) but it is largely more trouble than it is worth and it would still tarnish. Electroplating nickel on copper would be my first choice because it is easy to do well but there are other chemical surface finishes which could be used. Or send it off before final assembly to a professional to plate it.I have an idea for the next helical resonator that I build which will include variable coupling. That one I might try silver plating because it will have finger wiping surfaces.(1) It is the second helical resonator I ever built (3) and it shows its age. It works fantastic but overcoupling resulted in about 0.05dB of loss and a wide passband which has its advantages in some applications.(2) It is easier to make the resonator slightly larger to make up for the loss of Q if this is an issue. In a production environment, there is no reason not to silver plate it.(3) The first one was constructed like bd139's example but that was how I decided that double sided FR4 copper should always be used with overlaps for fillets on both the inside and outside for strength. Plus the extended sides allow the enclosure to sit flat when things like piston trimmers extend through the sides as shown.

author: coppercone2
author_rank: Super Contributor
timestamp: August 19, 2018, 08:14:10 pm
content: Assuming I found a copy of a expensive HFSS EM simulator that fell off the back of a truck, how difficult would it be to bodge a model of a waveguide made of PCB so I can determine what effects the solder bevels would have on the propagation characteristics?Is there a tutorial that shows you have to make the different shapes and set up the simulation? I never used 3d cad software before. I just wanna see a rectangle vs a rectangle with tiny solder bevels.I am looking a piece of brass waveguide coupler right now under a magnifier, and there is not really a discernible bevel with a standard magnifying glass. You can see some kind of edge discoloration but it seems pretty flat when held up to a light source. The edges on the exterior waveguide (which the signal goes through) look a bit galled towards the interior though, maybe from the mating process? It is around 10GHz.Is there any EM programs that I can upload a solidworks model into? (there is alot of youtube videos on how to make solidworks models but I really don't wanna learn how to make the same shit in a different program)I get the idea of how 3d cad programs work, but I feel that I am going to get clobbered by hard to find menu settings and stuff.oh i might be in buisness,http://www.padtinc.com/blog/the-focus/importing-and-splitting-solid-models-for-ansys-hfss-18-0

author: David Hess
author_rank: Super Contributor
timestamp: August 19, 2018, 08:21:38 pm
content: Actually if I electroplated the outside, then I would bead blast it or coarse sand it first to lower glare. In that respect, tarnished copper is actually pretty good.

author: coppercone2
author_rank: Super Contributor
timestamp: August 19, 2018, 08:22:53 pm
content: I am running an experiment to see how well car wax does at oxidation prevention on some old step stool I sanded last night

author: bd139
author_rank: Super Contributor
timestamp: August 19, 2018, 08:25:03 pm
content: Notes here on copper tarnish and lacquer:https://aa7ee.wordpress.com/2015/10/21/how-do-lacquered-boards-stand-up-over-time/

author: coppercone2
author_rank: Super Contributor
timestamp: August 20, 2018, 07:05:25 pm
content: I found this on microwave 101"Electronic discharge machining waveguideThere are two types of electronic discharge machining: wire EDM and plunge EDM. Both methods use high-voltage to melt away metal, rather than mechanically removing metal with cutting tools.Wire EDM uses a very thin wire that travels from one spool to another, is energized with high voltage, and is placed in contact with the part being machined to make a linear cut by blasting away material. Picture a tiny, round bandsaw... The part being machined is typically held stationary, while the two spool feeds are moved to steer the saw. In the best wire EDM machines, the top and bottom spools can be moved independently. This allows more complex shapes, for example, a cone can easily be machined. The part being machined is suspended in an oil solution, which is used to carry away and suspend the machining "dust". The accuracy of modern wire EDM machines is one mil or even better. Wire diameter for wire EDM is typically just a few mils, and brass is the material of choice. A five-mil brass wire will allow you to cut a 2.5 mil inside radius on your waveguide part.Plunge EDM uses carbon elements that are energized to high voltage, and are pushed into the part being machined to blast away unwanted material. The part being machined is suspended in an oil solution. The plunger can be a complex shape, and can be moved in X, Y, and Z axis, as well as rotated, enabling more complex shapes than wire EDM. Accuracy is better than one mil. Plunge EDM is far more expensive than wire EDM, because the plunger must be machined, and it has a short life. Plunge EDM is best used in tool and die manufacturing, or creating extremely accurate molds for injection-molding plastic parts. The expensive but highly accurate plunge-EDM part that is then used to create thousands more parts."It seems that they manufacture waveguide using EDM, so unless they follow it up with some kind of shaper, the waveguide will tolerate 0.0025 radius, which maybe achievable with fine solder in a PCB board corner. You would just need to make the side flat and use right angle blocks while gluing it to make it perpendicularI also think that using technologies like indium corporation nanofoil might be a good option for sealing your waveguide parts without a bevel or warping.

author: Wolfgang
author_rank: Super Contributor
timestamp: August 21, 2018, 10:56:55 am
content: Hi CopperCone2,with "properly plated" I mean that the surface of the enclosures should be:- Never made of Aluminum because of the immanent oxide layer that does not conduct very well- either have a Nickel or better a Silver surface plated eletrolytically- be as even as possible. Roughness values should be reduced by fine polishing.- The same goes for the lidOn top of that the lid should be screwed onto the enclosure with screws apart only a fraction of the shortest wavelength involved.I have these wisdoms from a guy working at Rohde & Schwarz in a GHz lab. I do not have any papers giving these in writing, but there probably are textbooks about microwave construction techniques where these could be looked up.When you look at microwave magazine or other tech newspaper on the subject, you get an idea of how its done.me personally had one unit (an oscillator enclosure ) made once, it worked fine, but I saw only a very subtle difference to a homebrew unit in a tinplate can where lid was not even soldered on the case. The frequency was in the 23cm band.Sorry for no more detailed info.

author: mc172
author_rank: Frequent Contributor
timestamp: August 21, 2018, 11:14:15 am
content: Aluminium is fine if you chromate convert the surface (and still comply with RoHS). Find somewhere that uses a trivalent chromate conversion process and you'll be OK. I regularly get 110 dB shielding effectiveness or better using this method.

author: coppercone2
author_rank: Super Contributor
timestamp: August 21, 2018, 12:10:49 pm
content: When you chrome, do you need hard chrome layer or will a thin chrome layer done at home work?I have been researching chromeplating and it seems you can do a decent job so long that1) you clean everything well2) maintain bath temperature3) maintain the hexavalent chrome level in your plating bath during the chroming process, but I would imagine depletion is only a problem if you do thick layersObviously disposing of chrome has difficulties but so long you are not running a factory and you control fumes it should be ok.The problem I thought chrome plating would have it its porosity and difficulty of polishing, and the cracks that form in it. How thick must the chrome be for RF use?And how do RF fingers compare to screws? They are spaced ALOT finer then you can do with screws unless you go insane with screw density.For one off prototypes I figured that using copper and silver plating it would be a better solution, with the only problem being its lack of dimensional stability, which I hoped that the beryllium copper RF gasket fingers would help with, along with torque specified screws. You can probably solder the gaskets down to your lid too, I figure adhesive would do a relatively poor job.At 50 GHz your wavelength is 6mm, and the RF fingers are spaced like 0.9mm. I am especially interested to know what happens if you stagger two layers, so the voids between the RF fingers do not go through, so the path requires a bend around another set of fingers.I assume the area between two fingers is like a little waveguide right? You no longer really use the slot antenna equation anymore since its long? So its different then vent holes.The foam I have no idea how to model. I think it might be worse since the metal coated polyester/nylon foam material has a much worse conductivity then berylium copper.When I look at the dimensions of a compressed finger gasket, I can kind of imagine something like a 0.7mm x 5mm (long) x 1mm waveguide section in the area between the fingers. This seems like it would only conduct milometer waves. On paper this is similar to a WR7 waveguide, which is rated for 110-170GHz. The foam seems like it would not have waveguide behavior, instead its main problem would be poor resistance, but the cutoff frequency would be insanely high. I can barely see light propagating through it.From my previous research you can't really relate it to vent holes, which are typically made in very thin metal, so they don't really have a true waveguide behavior (as compared to RFI fingers) due to them only being like 1mm long, since metal chassis is typically very thin. 14 gauge steel is only 2mm and that would be a beefy chassis, and they are typically like 3-4 mm wide. The RFI honeycomb transforms it into a waveguide I guess? A RFI honey comb that is 1/4 inch thick (6mm) offers around 50dB attenuation @ 10GHz, and the holes are like 3mm.When I think about mating surfaces though, they will be very tight, but I guess you would have a void resting between asparities in the metal. I don't know how to model this at all. I have a hard time imaging a wave propagating through it at all.Does anyone have any more details?

author: mc172
author_rank: Frequent Contributor
timestamp: August 21, 2018, 12:41:40 pm
content: It's not chrome plating, it's chromate conversion. It's a way of making the surface of the aluminium conductive and corrosion resistant.https://en.wikipedia.org/wiki/Chromate_conversion_coatingWhat's with the new username anyway?

author: coppercone2
author_rank: Super Contributor
timestamp: August 21, 2018, 07:30:01 pm
content: some fuckup with the password and email change then I decided not to change email but it would not send a activation email to my old email so the old account password works but its not verified or something like that, I managed to do something to de-activate itI don't think there is a 'ethical' way to reactivate the old one based on the process I used, from the prospective of the admins, I believe if I asked to revert it, that method can be used to social engineer/compromise an account, so the precedent should not be made, incase I am a coppercone imposter, so you will need to live with the uncertainty I did not murder the old one and steal his identity. I think I copy pasted my password as the email name or something during the account password change instead of copy pasting the new email in the field.Also, why chrome for RF? How come they don't have some kind of gold or silver plating for aluminum process, I guess other then areas where you make physical contact... given all the trouble they go through to gold plate RF stuff. Since its a skin effect, don't you lose the RF skin benefit of aluminum if you chromate it? Can you explain what the difference is between chromate conversion and really thin chrome plating? Do you form some kind of alcr alloy on the skin chemically? Or is the partial dielectric of the aluminum oxide worse then the chrome for RF purposes (it becomes a partially dielectric filled waveguide with oxidized)?Actually it seems to say its a nonconductive layer of chromium oxide an hydroxide. How does that help with seals? Is it just that it has a specified thickness and its softer then the aluminum oxide so you can break the surface better with screw pressure?I would imagine the best would be to put a harder chrome layer on the mating surfaces which get physical pressure applied on them to form the seal, and gold or silver on the interior surfaces to minimize impedance, by using a masking process.Looks like the main problem is the same, nasty carcinogenic hexavalent chromium is used for chromate conversion.don't spill that in your garage hehe

author: coppercone2
author_rank: Super Contributor
timestamp: August 21, 2018, 07:59:27 pm
content: Also what are the specs of the shield cans you make from the machine shop to get that 110dB (across what frequency range) attenuation?Surface finish (Ra), dimensional flatness (across what distance) and thickness.

author: mc172
author_rank: Frequent Contributor
timestamp: August 22, 2018, 11:11:23 am
content: With something properly designed I'd expect to see 110 dB up to 3 GHz. Above that I run out of permanent test equipment so don't get to do it too often.This is all a bit hard to put in writing or even describe. Every solution looks different and most of the time it's just what looks about right and is common sense. There is no one universal screening can, no one universal thickness or ratio of thickness vs width or whatever. One solution might be a copper sheet can with soldered joints, another might be a CNC machined aluminium billet. They will probably both achieve 100 dB, or whatever, I don't know.I don't believe that there are any hard and fast rules when it comes to shielding. You just have to build it and see!Things like surface roughness and thickness depend on how cheaply you've got to make it. You could even use a die-cast shielding can and fit a conductive gasket, but not one of those "conductive" rubber ones - they're only good for about 45-50 dB up to 1 GHz if you're lucky. But this may be enough for what you're doing.I don't think that surface roughness is too important on the mating faces. You could argue that a rougher surface (to a point) helps you as it has a bit more "bite". I wouldn't deliberately specify anything finer than 1.6 μm as I doubt it would help you in any way other than to increase the cost.I tend to not even bother specifying surface roughness. Most of the things I've worked on are probably around this figure or maybe slightly finer, but by accident (that's how they machined it - we didn't specify it) as most good machine shops just won't deliver something with a rough finish. However, I would hazard a guess that anything up to 3.2 μm roughness would still work fine. Maybe more, never tried!More critical is the distance between screws and how much preload you can generate on each one without yielding the bolts or cracking capacitors etc. but again, common sense, you don't need to go mad. Having said that, this is assuming your typical "billet" style shielding lid type thing. In the past I designed an RF product going up to 3 GHz which has a screw spacing of 84 mm, only has four screws (which contribute nothing to the shielding performance) and uses a stainless steel lid with sprung fingers. It clears 90 dB up to 1 GHz and 75 dB up to 3 GHz. Quite different but still performs very well.A bit more about good machine shops: don't be lured in by the cheap Chinese rapid prototypers. They just do not understand tolerances of any description and will not conform to anything you put on a drawing, even if you explicitly tell them in person about a critical feature. I've tried about 6, maybe 7 different CNC shops out there now and all of them are the same. They just cannot do anything to tolerance, no matter how basic the request is, i.e. drill and ream a hole. Will they ream it? No, they'll drill it oversize so that everything "fits together easily".The flatness of the final part is largely a function of its wall thickness, which is usually driven by how thick you can make it before it hits the thing nearest it. A thinner shielding can will be more likely to bend to conform to any mismatches in flatness between all of the mating surfaces, which can be quite helpful. This is further helped if you have lots of clamping bolts. But you're not going to want to rely on this to get it to perform well, that's not good practice. How flat does it need to be? Well, this is where you earn your money.The bit about chrome, skin effect etc. - I have no idea. I've sat and thought about this for too long and have gone round in circles. If you test a gold plated connector, it performs as well as a nickel plated one of similar design, despite the skin depth being ten times that of the nickel plated one and the plating being put on ten times thinner than the nickel one!It's not practical to electroplate aluminium.I feel knackered after writing this and I've not even attempted to answer two thirds of your questions, I must have re-written this four or five times and I'm still not happy with it but I could be here all day.You seem to be asking a lot of questions about shielding, skin effect, etc. Do you have a specific problem that you need to overcome? It's quite hard to offer sound, practical advice other than "you have to just build it" and "what you're asking depends on what the design requirements are".The best advice I think I can give is this. Go and build lots of different things before you venture anywhere near a simulator of such complexity.

author: coppercone2
author_rank: Super Contributor
timestamp: August 22, 2018, 12:49:01 pm
content: I have to go some where but I want to know these things so I can imagine how I will budget things and how RF related design things fit into my overall scientific/mechanical aspirations when it comes to equipment ownership, plating baths, etc.When I spend money on my own stuff I wanna be able to hit as many birds as possible with one stone, so if I know alot of specifications and stuff I can think ahead and not end up with stuff only useful for one purpose.And I feel all the information you provided will help me hit a finer target when I actually do try.

author: coppercone2
author_rank: Super Contributor
timestamp: August 22, 2018, 11:20:39 pm
content: If you want to test a specific seal, what kind of radiator would you put in the box to take measurements where the radiation being emitted from the antenna is not effected by the lid of the box being applied? Like if I just made a box with a coaxial connector going into it. Just solder a short wire stub on there? Lead into the middle of the box with a coaxial cable thats stripped? make a little loop? The efficency of the antenna should not matter because I would be making ratiometric measurements with a spectrum analyzer.I can pick frequency points that are not interfered with on my external receiving antenna (bicone)Like, it seems no matter if you put the transmitter or the reciever into a open box, you form a waveguide that is open to free space, so its like a narrow band directional antenna. How do you normalize this? Or do you just do a no box and closed box measurement?

author: mc172
author_rank: Frequent Contributor
timestamp: August 23, 2018, 07:57:52 am
content: You wouldn't do it that way. You'd stick the lot inside a chamber which has a close to uniform field strength, and at a known strength and measure what comes out.