Small RF enclosures (for SMA to SMA connections in terms of size) - Page 1
Forum section: electronics / projects

author: 6SN7WGTB
author_rank: Regular Contributor
timestamp: April 16, 2022, 07:39:09 pm
content: Am looking for some small shielded enclosures for Rf devices like filters, VNA protectors, etc.Around 40mm long, 20mm high, 30mm wide - typically as you find RF filters being sold in - usually extruded ali shell, and ali panel ends. And takes a PCB so maybe grooved inside.I've lost the will to live trying to search in RS or Mouser - just cannot get to shat I am looking for...An example of what would be ideal is the sort of enclosure a Flamingo FM notch filter comes in.Can anyone point me in the right sort of direction?Thanks!

author: reboots
author_rank: Regular Contributor
timestamp: April 16, 2022, 08:42:54 pm
content: For commercial or industrial use, Pomona Electronics makes compact enclosures prepped with RF connectors. For example, Pomona #2399 is SMA M-M. They are die cast rather than extruded. Prepare yourself for commercial or industrial pricing.https://www.pomonaelectronics.com/products/boxes/boxes-with-connectorsHammond Manufacturing makes more economical extruded aluminum enclosures. It's not clear to me whether the metal end cap variants are RF shielded.https://www.hammfg.com/electronics/small-case/extruded/1455I don't see anything specifically matching your size and feature requirements. The Flamingo filters are almost certainly using a generic Asian OEM enclosure, rather than a name-brand part you might find from a domestic distributor. Given thelow cost, it might be worth it to buy the filters just for the enclosure and included connectors.

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: April 16, 2022, 10:03:58 pm
content: Twin IndustriesMicro-Ampseries of enclosures is available with SMAs on either side, and a range of pre-made PCBs with pads for amplifiers, filters and the like. They're available from Digi-key.There's alsoModpak, but you'd have to order from them direct.

author: cdev
author_rank: Super Contributor
timestamp: April 16, 2022, 11:15:43 pm
content: There are active RF devices on ali-expressthat are definitely worth buying just for the cases.They have some LNAs that appear to come in cases that don't seem available elsewhere. (If you find some please let us know here!)The LNAs that come in these cases havenotbeen reviewed as very good by people here, however. They use fake counterfeit chips, its likely.But the case is nice looking. It may be broken in some other way, but in the photos, the cases look decent. Are they? It seems hard to fake that. They just have a machine shop and made them. Why not do that here? Well, no reason exists. They would sell.One could it seems almost certain make ones own LNA of the exact right size and shape, use MiniCircuits LNA devices , and get a very nice amplifier. IMHO the case does make a big difference in how well an LNA works. It can exclude RFI that otherwise would almost invariably sneak into the signal chain, for example.Some of my LNAs live in the small die cast Pomona boxes. However, if I do that again I will have to size the LNA expressly to fit snugly (around the edges) in a specific box.My LNAs use a combination of edge mount connector on the input side and a very short piece of coax on the other side. (less than an inch)That works well. The coax has to be soldered to both sides of the PCB quite well.

author: cdev
author_rank: Super Contributor
timestamp: April 16, 2022, 11:30:49 pm
content: How are their prices?If I hadn't gotten a very good deal on my Pomona boxes I wouldn't have gotten them. They are too expensive. I'd have made cases using other small product boxes, copper pipes and sheet copper, (that works well) or bought cheap chinese LNAs with nice boxes and put my own LNAs in them. (why not?)Quote from: radar_macgyver on April 16, 2022, 10:03:58 pm

author: hagster
author_rank: Frequent Contributor
timestamp: April 17, 2022, 06:59:42 am
content: What frequency are you working at? Those Pomona boxes look pretty awful for anything near the GHz.

author: 6SN7WGTB
author_rank: Regular Contributor
timestamp: April 17, 2022, 07:39:44 am
content: Yes, sorry, I should have stated my potential use.My requirements are all sub-140MHz - i.e. broadcast through to air band spectrum so although the Pomona look suitable, they’d be just too expensive. Similarly TI.The Hammond are an option - I missed the extruded ones with metal ends - kept hitting up on the plastic end ones (which I’ve used to make IR transmitters).Probably buying some populated cheapos and stripping them is the answer.

author: geggi1
author_rank: Frequent Contributor
timestamp: April 17, 2022, 10:01:51 am
content: Make the boxes!Get some pices of thin copper foil 0,2-0,5mm thick.You will also need a pair of long jaw thin snips or a heavy duty scissor.A small wice is also handy together with some wooden blocks.The wooden blocks and the wice is your bending jig.Make a drawing of the box full scale and glue this to the top of your copper foil. The glue can be made of flour and water.Cut and bend along the lines on your drawing.If you are making many boxes with the same you can make wooden blocks that fits inside the box you are planning to make and use this as a bending jig.

author: 6SN7WGTB
author_rank: Regular Contributor
timestamp: April 17, 2022, 11:00:46 am
content: It's a good suggestion as I do have brass sheet, some simple metal folding equipment that I use for modelling work.

author: 2N3055
author_rank: Super Contributor
timestamp: April 17, 2022, 02:19:25 pm
content: search for "5pcs Extruded PCB Aluminum Box Black Enclosure Electronic Project DIY 50*25*25mm" on Ebay..

author: cdev
author_rank: Super Contributor
timestamp: April 17, 2022, 02:35:25 pm
content: I have what is known here as flashing copper, thin copper sheeting. Its thicker than foil but not rgid enough to stand up to much bending. Layered over something it makes okay RF shielding, however. It must be combined with something to give it rigidity. That also applies to copper tape. One could make cases out of something else and cover them with copper tape.Anything is better than paying $40-120.00! (for an RF box suitable for agoodLNA)That's what some would likely charge for one to be made up. That's way too much.

author: cdev
author_rank: Super Contributor
timestamp: April 17, 2022, 03:48:34 pm
content: I have used that box. Be aware that its anodized. I have one of them here, right here, right now. I think the black coating is quite nonconductive. Other than that its sturdy. One can use sandpaper to scrape off the anodized coating on the edges, making it conductive where the edges meet. Also, as it comes the screw holes are conductive. Which makes all the difference, ensuring its all at roughly the same potential. I am a stickler for that because I am convinced it effects the performance of an LNA made using a single active MMIC. (with a voltage regulator) Previously I performed numerous experients for myself usig various forms of shielding. I posted the impressions of how it affected received signals on other sites I was on at the time.Even wrapping the coax and LNA in aluminum foil helped visibly over an LNA with no shielding. Noise travels into the inputon the coax shieldwithout it. .So its crucial, if you want to receive the weak signals. In this case I was trying to receive weak VHF and UHF signals from central NJ on ham bands. They were signals that originated in known places. NOAA weather broadcasts are also good for this. For example, signals from Connecticut and Rhode Island for me stretch the limits of LOS reception. I suspect that this is a good strategy for optimizing your receive front end and antennas. Use signals which you know the origin of, by using sites like Repeater Book to find and identify signals from some distance away from your QTH.For example, I am some distance west of New York City and can receive some signals from New York City but not all of them. Similarly with boats at 162 Mhz. (AIS) in New York Harbor.Oh well.. I get some of them.If I had a tower, I could receive all of them. So,Yes, I think the little metal cases strike a decent balance between appearance and performance if you can live with the above issue. Formostapplications its fine. For a passive filter it would be fine. For a sensitive LNA, it depends on a lot of things. I would suggest either adding copper tape or using sandpaper to remove enough of the anodization to make the two edges conductive, and internally making sure the PCB edges made good electrical contact. Otherwise the lack of conductivity will act as a slot. Make sure the edges of your PCB make good contact. Use a combination edge mount, thread on SMA and solder itwell on both sides. Use that connector on theinputside.There is enough room on the ends to add a switch or a filter or capacitor RF feed through for DC, or a toggle switch, LED, whatever. I always put anything like that on the bottom facing metal part. A hole for air to prevent internal condensation might help.Quote from: 2N3055 on April 17, 2022, 02:19:25 pm

author: 6SN7WGTB
author_rank: Regular Contributor
timestamp: April 17, 2022, 04:15:44 pm
content: I may just resort to using small Hammond /Eddystone die-cast boxes.Can't really fault them. Nothing fancy but good flanged lid which should keep the Gremlins in or out.

author: cdev
author_rank: Super Contributor
timestamp: April 17, 2022, 04:40:28 pm
content: Quote from: 6SN7WGTB on April 17, 2022, 04:15:44 pmAs I said the four screws in the corners do make for an acceptable electrical connection for most uses.But the anodized black stuff isn't a conductor, its an insulator. You should know that the end result is a crappy RF box. Unless one does what I suggest to modify it. And even then it may not be so good. But, "better than nothing".I am thinking about an LNA, however which is an application that IMHO, demands a fairly decent RF box. If its not very well shielded, the amplifier does not ever reach its true potential. Noise gets inside.Don't forget that everything that gets in, just about, gets amplified.

author: 6SN7WGTB
author_rank: Regular Contributor
timestamp: April 17, 2022, 05:02:00 pm
content: Yes that's why I like the Hammond/Eddystone.

author: cdev
author_rank: Super Contributor
timestamp: April 17, 2022, 05:20:48 pm
content: The cases below would be okay for most uses, with the caveats I am mentioning. Copper tape via capacitance could be used to fix the edges to one another much better than they are by default. That works pretty well.PCB edges should be grounded to any case, also RF connectors should utilize both the case and the edge mount - both... Otherwise, problems arise.

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: April 17, 2022, 06:46:05 pm
content: Quote from: cdev on April 16, 2022, 11:30:49 pmTwin Industries boxes are about $110 on DK, so are pricey compared to Pomona etc., and are likely overkill for OP's frequency range. I've used them for filtered amps at 9.4 GHz with their PCBs (RO4350), have a design in the works using an MH-2 and my own PCB at 5.6 GHz. At sub 140 MHz, making your own boxes works, or else make a PCB to hold your parts, and build a box around the PCB using copper-plated FR4 or tape. The PCB becomes part of the enclosure.

author: jpanhalt
author_rank: Super Contributor
timestamp: April 17, 2022, 07:30:47 pm
content: It has been bugging me ever since I read the OP's post. A few years ago, I needed some RF enclosures. I finally remembered. My source was Teko (located in Italy) and now apparently sold by OKW (https://www.tekoenclosures.com/en/products/family/RF/series/37-39). They were attractively priced compared to DigiKey and Mouser.The version I got was 271.16 They are about 1.9" x 2.1" x 1" with both top and bottom having friction fits. Unfortunately, 271.16 is now a dead link. Glad I bought several at the time.EDIT: The other source I used was LMB Heeger (https://lmbheeger.com/search.aspx?find=M-16). The size I got was 2"x 1.75" x 0.75". Unfortunately that size does not appear to be available anymore. Moreover, they were solderable tops, not friction fit. But, still reasonable compared to brand name distributors.

author: cdev
author_rank: Super Contributor
timestamp: April 17, 2022, 08:14:33 pm
content: The extruded anodyzed aluminium cases like the ones Ive bought from ebay, would be okay for most uses, with the caveats I am mentioning. They are small and almost ideal in size for me.Unfortunately they are anodyzed which means the coating is an insulator.Copper tape via capacitance could be used to fix the edges to one another much better than they are by default. That works pretty well. The anodized material must be very thin, so taping over the gap using a conductive material tape will by virtue of capacitance, even if that is all thats available, connect the two well, with a low RF impedance. That works well. The reduction in potential common mode noise getting in seems quite significant.NASA construction guidelines for electronics often specify gold foil or silver plating for RF shielding. We should think of anodyzed coatings the same way we do of paint. Painted steel on computer cases often makes for a really crappy case that doesnt shield EMI at all. It may even make it worse, by acting as an antenna for it. To work as RF shielding, It has to be scraped off where the pieces of metal meet. Which is a real PITA.One can put copper tape on the areas where sheets of aluminum or steel meet. Even if the paint or anodyzed layer is left there, The capacitance likely offers a low enough impedance to RF to improve the shielding measurably.One company selling stuff to the RTLSDR market sells its hardware in anodyzed cases and seems to claim that they provide good RF shielding. Thats inaccurate. But for the specific use case, it is likely better than nothing, although likely not by very much. Is it shielding? Not really by much. its a missed opportunity to put some shielding there. Such a case is mechanical protection, from shorting, etc. which a bare PCB would be vulnerable to.

author: cdev
author_rank: Super Contributor
timestamp: April 20, 2022, 03:38:19 pm
content: Quote from: radar_macgyver on April 17, 2022, 06:46:05 pmI definitely agree with you on the need for RF friendlier cases at GHz frequencies. But why are they so expensive when they could be much cheaper?How good can they be? It all comes down to the fit, and how well is it possible to make the PCB fit snugly in the case.THis is all too wordy and kind of stupid..warning.. rant ahead..Lets suppose we have a small PCB that fits almost perfectly into the box. Which plane is it going to be in?How is it going to fit into the box. The Pomona box shaped aluminum cases, are die cast and fairly well designed and the lids have a small flange that makes for better than average (but not by much) RF shielding. Because it has a corner and a well-fitting lid.. (and four little screws which make the lid fit snugly. There are only two pieces of aluminium, the box and its lid and four little screws. Well, one could mount the PCB to the LID.. that would actually make sense for many projects.. but cosmetically, might be kind of ugly.. Lets suppose we do what they do with their own RF cases, and put the RF coaxial connectors on the ends.Here is their web page..https://www.pomonaelectronics.com/products/boxes/boxes-with-connectorsWell, immediately we see how they propose to do this grounding thing..With a tinned grounding post/screw."Screw, 4-40 UNC2A" Okay.. but, I personally don't feel so great doing that.. I feel better about the aforementioned dual edge mount /plus threaded SMAs. An N type connector which comes with a little tinned solderable connector would be better. But in any case, I'm confident that a good low impedance connection will get made, up to a couple of hundred MHz, where the wavelength starts getting shorter and shorter and the likelihood that the return path becomes some fairly high percentage of the actual return path to ground. Thats when things start acting up. Since its die cast and this wouldnt add much to the price, Pomona should put some provision in its boxes for grounding to the edge of PCBs. The hammond boxes intend that a PCB would go into ridges on the edges.. Instead of using the screw and anchor post? Maybe thats better for DC applications because getting a low resistance connection to aluminum is non optimal without lots of pressure as well as a clean connection. (Nobody's approach is that great, that I can see!)There has to be a better way to do this and whomever gets it first should do it, and make a decent amount of money with it.if it sits flat with the removable piece on top, suppose you have two SMAs, where are they going to be and how will they connect to the PCB? Will they be on the ends? Probably. Okay, how will they connect to the PCB, both top (signal trace?) and bottom, (ground?)What about the edges of the board? Will they be grounded, if so, how? Will the board sit in the box oriented on its side, What will be done at the ends, to ground it? Lets use one that I have as an example, it allows a 52mm PCB. If your PCF is exactly the right length you can ground it with the SMA jacks at its ends. Using an combination end launch and threaded gold plated SMA. Like the ones used in my NanoVNA 2That works best. The threaded portion is also deliberately long. One sould use it with a slightly shorter PCB (with room for the hex nuts) and get a fairly good electrical connection.At the ends.Do you see what I am getting at? An RF PCB should be grounded better especially around its edges.

author: metrologist
author_rank: Super Contributor
timestamp: April 20, 2022, 03:54:21 pm
content: What are prices like for these or for custom machined aluminum enclosures/clamshells? What does one want to pay?

author: cdev
author_rank: Super Contributor
timestamp: April 20, 2022, 04:15:58 pm
content: I first reaction was "do you really want to know"That being sort of a joke.. but not really.. Too much.. they want too much. Meaning there definitely is a potential profit there for somebody..One of the URLs in this thread goes to a manufacturer who wants and gets $120 for a two port box. Thats a lot. Perhaps not typical.I should send a thought out (actually he is very much in my thoughts today) to the very helpful @radiolistener who has helpfully often pointed me to online resources.. On aliexpress there is a manufacturer of LNAs who dresses their LNAs up in very pretty metal boxes..Probably for some reason the LNAs are not so very good. Not as good as the cases makes them look. In any cases the noise figures are not as advertised. Also the devices are not protected from ESD. But the boxes make it worth buying them, and using the PCB as a template to properly size your own LNA to put in the nice die cast box. Doing that one can save some money.Quote from: metrologist on April 20, 2022, 03:54:21 pmI would think that $20 would be fair and reasonable. $40 is too much.

author: metrologist
author_rank: Super Contributor
timestamp: April 20, 2022, 06:51:56 pm
content: I was curious from a prototyping POV. I did not make these, but I do have a full blown machine shop that is basically holding down the concrete floor right now.I was imagining the postman delivering chunks of aluminum. These I will repurpose for my use.

author: cdev
author_rank: Super Contributor
timestamp: April 20, 2022, 08:21:08 pm
content: Quote from: metrologist on April 20, 2022, 06:51:56 pmThe solid machined case style is excellent for RF but it uses up a lot of aluminum. Its not necessary for low noise amplifiers to be cut from a solid chunk of aluminum, although it doesn't hurt!A much more abbreviated case will work just fine. What's important is the enclosing of the RF path in conductive material completely which excludes radio waves from bypassing transmission lines.. .

author: KE5FX
author_rank: Super Contributor
timestamp: April 20, 2022, 08:38:23 pm
content: At the prices they charge for those ready-made enclosures, the real question is, "What's the cheapest desktop CNC machine that will hog out an aluminum cavity from a solid block?" It's safe to say that you could buy such a machine for the price of only a few of those Micro-Amp boxes.

author: hagster
author_rank: Frequent Contributor
timestamp: April 20, 2022, 09:14:16 pm
content: Quote from: 6SN7WGTB on April 17, 2022, 07:39:44 amAt those frequencies and with the size of your board, I don't think it's hugely important to have an amazing enclosure. Good PCB design will prevent your traces becoming antennas. If you do that, and with good filtering of the power lines I doubt you will notice the difference a custom made case makes. If you really want, you can get some PCB sheilds but I don't expect much difference.As normal, you ask a question on a forum and everyone will offer 101 problems, but unless you have some really special requirements, you can probably get away with either the belt or the braces, but you likely won't need both.

author: metrologist
author_rank: Super Contributor
timestamp: April 20, 2022, 09:31:18 pm
content: Quote from: cdev on April 20, 2022, 08:21:08 pmWe used to solder in tin fences around certain circuits and pop in mu metal lids. There are cheap ways to get things done. I remember using plumbing parts.Quote from: KE5FX on April 20, 2022, 08:38:23 pmYes, the cost of the machine is, irrelevant. That is the cheap part.But there is even an uglier side. You will find out that you can buy a cheap LNA with a machined aluminum enclosure WITH plated RF connectors for LESS than the hunk of aluminum to make just the enclosure.The only things I've made in my shop are things that you cannot buy, because this old adage is just too true: "For a little bit more, you can make it yourself!"

author: thm_w
author_rank: Super Contributor
timestamp: April 20, 2022, 09:49:06 pm
content: Quote from: metrologist on April 20, 2022, 09:31:18 pmCost of endmills, connectors, feed through, aluminum block, aluminum plate, screws, hours spent swearing as a shitty $250 CNC machine tries to cut into aluminum while you stand and baby it.Anyway here is one box for $15:https://www.aliexpress.com/item/32883971739.html

author: KE5FX
author_rank: Super Contributor
timestamp: April 20, 2022, 11:21:04 pm
content: Yep, that's probably the best answer. Going to be hard to beat $14 each.

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: April 22, 2022, 12:24:26 am
content: thm_w beat me to it, but this was the reason I fell down the CNC rabbit hole. I'm too far gone to get back out, but I strongly advise against the roll your own approach unless you like machining as a hobby.The Aliexpress amplifiers look interesting. Good for one-offs. Don't have the convenience of the micro-amp pre-made PCBs though.

author: cdev
author_rank: Super Contributor
timestamp: April 24, 2022, 02:10:55 am
content: bluetosis?Four screws for mounting its corners..