Pomona BNC boxes - Page 1
Forum section: electronics / rf-microwave

author: KenGaler
author_rank: Contributor
timestamp: December 11, 2016, 06:27:24 pm
content: Anybody know of an alternate to these Pomona boxes? My butt hurts just thinking about $30 each.If there are no other good choices, does anybody make proto pcbs for them?TxKen

author: Fraser
author_rank: Super Contributor
timestamp: December 20, 2016, 07:24:38 pm
content: I have used even bitter BNC project boxes that came from Radio Spares in the UK. Sadly I think they cost about the same as the Pomona offering though. These boxes have always been a tad pricey. For small projects I had to drill the BNC holes in Hammond/Eddystone diecast boxes and fit panel mount connectors. In terms of the time it takes, a commercial project would likely buy the Pomona 'ready to use' product.Sorry I cannot help. I would be interested in alternatives also.Fraser

author: SingedFingers
author_rank: Frequent Contributor
timestamp: December 20, 2016, 07:53:24 pm
content: I managed to pick up a couple of these, used (just attenuator networks in them) in a box of assorted junk on eBay. £5 for two in the end. Plus some old OC81D transistors that went back on ebay for a small fortune. Couldn't believe my luck.However they're really "not all that". I'd be annoyed if I bought a new one come to think of it. You can do the same with a couple of bulkhead mount BNC connectors and a die cast aluminium box with a few holes drilled. Plus I usually need a switch or something as well which hurts if you have to blow a hole in a Pomona one.I haven't used a prototype board in mine. Just wired rat's nest.

author: Fraser
author_rank: Super Contributor
timestamp: December 20, 2016, 08:15:30 pm
content: I agree. The Pomona boxes are not that great.The RS BNC project boxes used two large square flange connectors and a rectangular two piece shell between them. This gave great access to what was being constructed within. Nice quality construction and very solid in use. I have used dozens of these during my career in RF. Modern kit often uses SMA connectors which was not available in that particular case range. There were N type and PL/SO239 versions. I see that RS no longer sells them. I have five or so in my project stock though.Regarding NOS Germanium transistors...... I almost binned a bag of OC and AC series last week. I shall have to place them on eBay 😄Fraser

author: Gyro
author_rank: Super Contributor
timestamp: December 20, 2016, 08:58:36 pm
content: I think this is the one you mean Fraser. I used my only one recently avter having it for about 20 years. A shame to hear that they don't sell them any more (I hate using my last one of anything!).

author: Fraser
author_rank: Super Contributor
timestamp: December 20, 2016, 09:05:03 pm
content: @Gyro,Yes that is one of the versions I have. There is also a slightly different version that I have which has 'L' shaped side panels that lock together and long threaded rods slide through them to secure everything together. I will did one out and photograph it later.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: December 20, 2016, 09:18:32 pm
content: OK, I found a few of the RS type boxes on the shelf in my lab. I have several more squirreled away somewhere !Sadly I do not know who actually manufactured these boxes as they may still be in production somewhere.The last time I bought one of these it was £15 +VAT so they were never cheap. That was about 10 years ago.RS datasheet attachedFraser

author: Fraser
author_rank: Super Contributor
timestamp: December 20, 2016, 09:28:40 pm
content: The original RS boxes were made byTYCO Electronicsand have now been replaced with a cylindrical version found herehttp://uk.rs-online.com/web/p/rf-coaxial-adapters/3950447/Datasheet of the new version attached.I prefer a flat face box for when buttons or sockets need to be fitted into the shell.Fraser

author: Gyro
author_rank: Super Contributor
timestamp: December 20, 2016, 09:49:53 pm
content: QuoteThey could have given some indication of how much space there is inside.Being RS own brand I don't know how you'd find out any more. Only available in 75R too.Presumably that screw on the side allows the thin walled cylinder to slide off. The countersunk screws at the ends look quite meaty so it might be tight in there!It's about time someone in China started running off those extrusions.

author: SingedFingers
author_rank: Frequent Contributor
timestamp: December 20, 2016, 10:03:55 pm
content: Not sure I like cylindrical ones. It's much easier to screw up and not be able to get the cover on. The old RS ones look nice: will keep an eBay eye peeled for some.Gyro: nice idea for a prescaler BTW assuming that is what it is. Need to build one of them myself when I get time as my counter is only good to 22MHz which sucks (disclaimer: homebrew thing mistakenly built on stripboard in the 1990s)Fraser: some crazy person paid £13 each for some OC81Ds. Even had some American guy almost have a nervous breakdown because I wouldn't ship outside UK. Find the lowest price ones in the UK and undercut them with a buy it now by only £0.01. Easy money.

author: Gyro
author_rank: Super Contributor
timestamp: December 20, 2016, 10:22:36 pm
content: QuoteProject link if it helps...https://www.eevblog.com/forum/projects/my-600mhz-prescaler-(from-the-scrap-box)/msg1074092/#msg1074092Manhattan beats stripboard every time.

author: SingedFingers
author_rank: Frequent Contributor
timestamp: December 20, 2016, 11:22:43 pm
content: Thanks for the link. Will read

author: karoru
author_rank: Regular Contributor
timestamp: December 21, 2016, 05:35:15 pm
content: Quote from: Gyro on December 20, 2016, 09:49:53 pmReally, there should be some award for the guy that made this technical drawing and didn't notice that there's something "kind of" important missing:)

author: Fraser
author_rank: Super Contributor
timestamp: December 21, 2016, 05:50:25 pm
content: I should state that China-RF and other ebay sellers have nice small aluminium enclosures very similar to the original RS design. The end plates would need to be drilled or punched to take a panel mount BNC connector. They are pretty cheap at around $2 a piece, but the time to convert them to BNC in line boxes could still make it uneconomic to do.http://www.ebay.co.uk/itm/New-Extruded-Aluminum-Box-Enclosure-Case-Project-electronic-DIY-50-25-25mm-/111801450858?hash=item1a07e2c16a:g:Z1AAAOSwr7ZW5pk3http://www.ebay.co.uk/itm/Black-Extruded-Aluminum-Project-Box-Enclosure-Case-Electronic-DIY-50-25-25mm-/131630608758?hash=item1ea5cbb176:g:NQgAAOSwoBtW5pk4http://www.ebay.co.uk/itm/Aluminum-PCB-Shell-Extruded-Black-Enclosure-Box-DIY-Project-Case-40-25-25mm-/401084062644?hash=item5d62791bb4:g:dkoAAOSwZ1lWc1pEhttp://www.ebay.co.uk/itm/New-Extruded-Aluminum-Box-Enclosure-Case-Project-Electronic-1-97x0-98x0-98-/162187858992?hash=item25c3265430:g:4wkAAOSwFe5Xx~bZhttp://www.ebay.co.uk/itm/Aluminum-Blue-Box-Enclosure-Electronic-Project-Case-25-25-80mm-/112169283392?hash=item1a1dcf6f40:g:DHcAAOSwmLlYBDCKFraser

author: KJDS
author_rank: Super Contributor
timestamp: December 21, 2016, 09:29:57 pm
content: I'll have to have a root through my old drawers to see what germanium parts I have.For boxes, I've often just cut up some double sided board and soldered it together.

author: cdev
author_rank: Super Contributor
timestamp: December 22, 2016, 04:43:55 pm
content: You likely can also use a short length of thin copper pipe for some project boxes. If the PCB can be cut to fit in it and the RF connector isn't too big.For an inline trap or band pass filter, for example, if its small, that might make a lot of sense. It certainly would be a lot cheaper than those die cast aluminum boxes and also copper is a better conductor.

author: Fraser
author_rank: Super Contributor
timestamp: December 22, 2016, 05:29:54 pm
content: I just managed to buy 14 of these nice RS format rectangular in line boxes with nice black cases. Brand new and unused. They are a nice mix of good quality N type and BNC type connectors plus two lengths of case, 65mm and 75mm. The cost? £43These will keep me going for a while 🙂Sadly that was all of the chaps stock or I would provide his details.Fraser

author: SingedFingers
author_rank: Frequent Contributor
timestamp: December 22, 2016, 06:00:59 pm
content: Good price!

author: Fraser
author_rank: Super Contributor
timestamp: December 22, 2016, 06:07:16 pm
content: I thought so, hence buying his entire stockFraser

author: Gyro
author_rank: Super Contributor
timestamp: December 22, 2016, 06:26:18 pm
content: We need an emoticon for 'Green with envy'.The China extrusion boxes would be good if you could get the original large flange BNC connectors (presumably they are the same flange size as N type).

author: GreyWoolfe
author_rank: Unknown
timestamp: December 23, 2016, 03:20:55 pm
content: Quote from: Gyro on December 22, 2016, 06:26:18 pm

author: KenGaler
author_rank: Contributor
timestamp: December 23, 2016, 04:53:34 pm
content: I've been looking at those boxes from ebay also. This one for instance.http://tinyurl.com/hqmhmm9I'm considering using these but with PCB end plates. It wouldn't be difficult to design a family of PCBs in a small panel that would consist of:- Two end plates for each of BNC, SMA, and N connectors. These connectors could be the type that edge connects to the internal PCB. This is a good example:http://tinyurl.com/glq2kmshttp://tinyurl.com/z5nweojhttp://tinyurl.com/hrwsjdv- And internal boards with a 50 or 75 ohm stripline connecting the connectors. The line can be cut to add series parts.This kit of break-off PCBs along with the $2 enclosure would be useful and a LOT cheaper than the Pomona boxes.It's hard to describe. Do you know what I mean?Ken

author: SingedFingers
author_rank: Frequent Contributor
timestamp: December 23, 2016, 05:06:25 pm
content: Good idea with PCB based ends. Cheap and easy then!

author: cncjerry
author_rank: Unknown
timestamp: December 26, 2016, 05:54:28 pm
content: Those cylindrical boxes changed my builds for sure. Having tons of pipe and a CNC metal lathe, I can know them out quickly. The only issue is mounting the PCB, but if you make it a snug diametrical fit, the likelihood of the parts grounding is mitigated. I've been using the little bud boxes but having to cut a D in the end (and sides for reflection bridges) was a pain and I never had the right size. Now looking at the cylindrical boxes, I can use even metal pipe for more shielding and I picked up a ton of end cap sized cutoffs for free a while back. Also, being cylindrical, they give a better look to in-line filters, etc.

author: cdev
author_rank: Super Contributor
timestamp: December 26, 2016, 07:56:01 pm
content: For using small boxes.. this kind of SMA connector is useful in grounding to both sides of both ends of the PCB and the box effectively, and not just one or the other.Edit: You can buy these with a nut and lock washer, thats what I meant, (the pictured one doesn't have them). These are useful with the small die-cast Pomona boxes (the ones that don't come with coax connectors pre- attached) too.

author: Spikee
author_rank: Frequent Contributor
timestamp: December 27, 2016, 07:06:52 am
content: If those end plates of the china like extrusion boxes is not good for the BNC you van always design your own endcap and getit made and anodized in china. This is cheap, even in small qty.If you guys can get a decent order together (>50 pcs) of custom end-plates than I can do this for you guys if you want it.

author: David Hess
author_rank: Super Contributor
timestamp: December 28, 2016, 05:25:19 am
content: It would be nice if all inside surfaces of the boxes were solderable. I usually end up making my own out of double sided copper board with solder fillets on both sides for strength.

author: SingedFingers
author_rank: Frequent Contributor
timestamp: December 28, 2016, 10:01:59 am
content: That's how i built my frequency counter enclosure. It's incredibly strong if you use FR4.

author: Robert763
author_rank: Super Contributor
timestamp: January 01, 2017, 02:57:45 pm
content: The "RS" boxes with two "L" extrusions are actually a Greenpar design. Ma-Com/Tyco bought out Greenpar. I have a couple that have the Greenpar interseries interface on the end plates so you can put any connector on them. The blue ones with "U" extrusions are Huber + Suhner Sucobox, nice but not cheap. The Pomona boxes have poor shielding and this can also be an issue with the Chinese boxes as they are anodised all over.

author: jpb
author_rank: Super Contributor
timestamp: January 13, 2017, 10:46:52 pm
content: If $30 in the USA seems expensive, the Pomena BNC boxes are frighteningly priced in the UK.At Mouser the plain ones are £28:56 + VAT (i.e. £34.27 inc VAT) whilst the ones with banana plug connectors are £55:54 + VAT (£66:65 including VAT).But even more outrageous is the price for the same at Farnell £62.284 + VAT = £74:74 inc VAT for the plain one :http://uk.farnell.com/pomona/2390/box-shielded-aluminium-blue/dp/1228237?ost=Pomona+2390&selectedCategoryId=&categoryNameResp=All%2BCategories&searchView=table&iscrfnonsku=falseSo US price = $30 Farnell price = $91, three times the price.The alternative of buying an enclosure for around £3 plus two BNC jacks at say £3:50 each comes to around £10. I would be happy paying twice that, say £20 for the Pomena box but 3 1/2 times to over seven times is just madness.

author: Fraser
author_rank: Super Contributor
timestamp: January 13, 2017, 11:33:59 pm
content: My parcel of boxes arrived. They are really nice quality boxes with high quality N and BNC connectors. I have seen them before on a power inserter for an active Schaffner (?) EMC probe. They look like they are an expensive item.Looks like I have enough for many years to comeFraser

author: Fraser
author_rank: Super Contributor
timestamp: January 13, 2017, 11:41:02 pm
content: Just saw an interesting variation in use of theses boxes. One attachec axialy to another with a metal screen between the two for a multi stage device. Never seen that before.

author: KenGaler
author_rank: Contributor
timestamp: February 02, 2017, 05:28:00 pm
content: These look good from Hammond.http://www.digikey.com/product-detail/en/hammond-manufacturing/1590A/HM150-ND/122740Ken

author: Fraser
author_rank: Super Contributor
timestamp: February 02, 2017, 06:54:27 pm
content: That is the classic 'Eddystone box' that has formed the heart of the project metal box market for many years. Excellent except that they do suffer surface oxidation if not painted. I have lost count of how many of those boxes I have seen and used in professional applications over the years.Fraser

author: SeanB
author_rank: Super Contributor
timestamp: February 02, 2017, 07:32:59 pm
content: Remember with those Eddystone cast boxes the cover is not really a shield, unless you first use a surface mill to trim the metal properly level, and the lid to make a flat mating surface, and then put a conformal tin or gold plated copper mesh gasket as a seal. Otherwise the as cast metal can have a thick oxide coating on it, which can be a pretty good insulator, and literally make the top an insulated cover that will radiate.

author: Fraser
author_rank: Super Contributor
timestamp: February 02, 2017, 07:45:37 pm
content: SeanB,Totally agree. For sensitive RF projects I used either an internal screened 'tin box' approach or a proper RF grade milled box with RF gaskets. Such specialist boxes are pricey though.Fraser

author: Gyro
author_rank: Super Contributor
timestamp: February 02, 2017, 09:05:50 pm
content: Quote from: Fraser on January 13, 2017, 11:41:02 pmLooks useful... but that poor BNC panel socket, some form of 'truss' might be in order!

author: Wolfgang
author_rank: Super Contributor
timestamp: August 15, 2018, 09:41:23 pm
content: Hi,I also use PCBs with edge mount connectors, but in tinplate "Schubert" boxes. They cost a fraction of the aluminum ones are have better screening, like this:https://electronicprojectsforfun.wordpress.com/working-with-rf-circuitry/

author: cdev
author_rank: Super Contributor
timestamp: August 17, 2018, 01:30:19 pm
content: So you simply cut a square hole in the Schubert box thats exactly the size of the SMA's square?Have you ever used the longer SMAs that have an extra length of threading for a pair of nuts and a lockwasher? The situation is a bit different that way. It may be better for shielding RF to use a longer SMA that makes more positive connection around the edges. They still are soldered to the edge of the device with their little "C's". But then the ends of the PCB are not snug against the ends of the box unless you can recess the SMA a bit. (I never have done that, instead I make a strip of copper flashing material, thats long enough to go around the PCB inside the box completely and some overlap, but holes for the smas, thin copper to improve the grounding, usually putting it on both sides of the PCB, top and bottom.) Aluminum boxes are not the best conductors because of oxidation so they benefit from some extra copper, I think. With a die cast box its a bit more difficult. For me sometimes I only do this on one side, the input side.(I've only done this for what I consider to be a critical application, low noise RF amplifiers that seem to perform quite differently depending on how they are enclosed.)Quote from: Wolfgang on August 15, 2018, 09:41:23 pmI'm going to look them up, thank you for the recommendation.Tin boxes are excellent! Tin is my favorite shielding material.A short length of copper pipe also works really well and is easy to work with if you use the threaded SMAs, (as long as you don't need to connect anything through the sides.) I've been too lazy to get caps so I've just used a bit of copper for the ends and folded and cut it, then soldered. That has worked well for me too. They are just large enough for a label.

author: Wolfgang
author_rank: Super Contributor
timestamp: August 17, 2018, 02:02:27 pm
content: Hi CDev,I usually do it in the following ways:- Order pre-drilled boxes from Schubert. Send them a drawing, and they make them for you for a moderate price.As you can see from my website, I standardized my projects a bit so I dont need too many types.- Sometimes I use plain boxes and drill in the lab. Then I use the "long" SMA edge mount connectors, and when you lookat my boxes I use a nut and a washer outside and I flush solder them to the box inside.- If I cannot use an edge mount connector due to PCB design I use long 90° connectors, again with nut and washer outsidethe case. Inside, I solder them to the case, too. Just just have to set them back a little from the PCB corners.- For special cases (Bruene bridge, some switches, ...) I use very long upright SMA connectors and drill holes in the case lid.These use a rubber gasket to press washer and nut to the lid inside, and an outside washer and nut fixes them and the lid.- I have a machine for punching square holes, but I almost never use it.