Pomona BNC boxes

[Spikee]

If those end plates of the china like extrusion boxes is not good for the BNC you van always design your own endcap and get
it 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.

[David Hess]

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.

[SingedFingers]

That's how i built my frequency counter enclosure. It's incredibly strong if you use FR4.

[Robert763]

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.

[jpb]

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=false

So 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.

[Fraser]

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 come

Fraser

[Fraser]

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.

[KenGaler]

These look good from Hammond.

http://www.digikey.com/product-detail/en/hammond-manufacturing/1590A/HM150-ND/122740



Ken

[Fraser]

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

[SeanB]

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.

[Fraser]

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

[Gyro]

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.

Looks useful... but that poor BNC panel socket, some form of 'truss' might be in order! 

[Wolfgang]

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/

[cdev]

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.)

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/

I'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.

[Wolfgang]

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 look
  at 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 outside
  the 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.