There are some really nice small enclosures that are incorporated into products sold by Mini-Circuits and others. They are very cool because their surfaces are perfectly perpendicular to each other, with no draft angle. This makes them perfect for joining modules together a bit like plumbing, and quick and easy connector alignment.
I didn’t know of any low-cost source of them (I could find low-cost angled sides, and really expensive ones with perpendicular sides but not low-cost), so I tried to make my own. This short blog post documents the method I attempted! The end result is physically larger, and won’t have the excellent performance of Mini-Circuits products, but could be acceptable for home use.
Apologies for the poor photo quality with some of the pics further below, some were taken with a mobile phone.
The technique could be used for non-RF circuits too. It all hinges around aluminium section, and a bit of metalwork that doesn't need many tools. A vice, hacksaw, file, electric drill, bits, , and is pretty much all that is required. An electric saw and disc sander will help though.
Take a length of box-section i.e. square-section extruded aluminium, and chop it to the right size (either with a hacksaw, or maybe a machine tool, but avoid a table saw - is really dangerous with alu box section!). Afterwards file it. That forms the body of the enclosure, and holes can be drilled for any RF connectors as required.
The photo shows my PCB too – just a double-sided copper-clad board, hand-cut/filed.
Next, for the end plates, I used 4mm thick aluminium sheet, cut and again filed. Thinner sheet could be used too.
If you want to, it could be possible to remove some thickness along the circumference on one side, to make the end plate pluggable onto the box-section. That’s not that easy to do however, without some machine tools.
Next, make some holes for screws (countersink them if you wish) on one end plate. For the other end plate the holes need to be smaller, and then tapped (I use a hand tap).
Drill holes on the sides of the extrusion for the RF connectors, and file, and optionally sand and polish everything, and voila, all of the metalwork is done!
For the insides, you could use copper-clad board cut to size, or a custom PCB. In the photo above, I chose to permanently solder the PCB to the nuts holding the SMA connector (easy to do with a soldering iron but needs a 3mm bit or larger, and 60W or more power ideally. This 90W model could be suitable: / / ). The SMA connectors were bolted on first, and then the nuts were soldered. There are star washers, to try to bite into the aluminium.
In future I may re-visit this soldered-nut method, but for now I went with it for my 5-200MHz intended use-case.
For the ground plane, I drilled lots of holes and soldered wire clippings through them to connect the top and bottom copper layers. For non-ground-plane connections, the drilled holes were given copper clearance with the countersink bit.
The wiring from the circuit was attached using short lengths of 30AWG kynar wire. This isn’t ideal, but I didn’t have time to design a PCB and get it made.
This is the underside, you can see the wiring here:
Here’s another example, where no PCB was used. I just soldered the metal can of the circuit (it was a filter) to the body of the connectors, and then made the rest of the connections using short lengths of enamelled copper wire. I’ve not made the end plates yet.
Here is the underside of the finished module, compared with the Mini-Circuits one. No real difference.
Afterwards, I just printed a design on paper and glued it onto the front. Not perfect, but it will do for now!
Here it is in use, it is being used in a ‘power splitter’ mode as wired in the photo above, converting a 20MHz input signal at 0dBm at the port marked 'J', into two approx -3dBm outputs (there will be some loss) that are 180 degrees out-of-phase with each other. You need same-length SMA cables for this, otherwise the phase will be noticeably wrong:
It would be interesting to see other people's custom enclosures too. Laser-cutters and 3D printers are definitely making life easier! Also, has anyone explored spraying an electrical screen to the insides of plastic?
Thanks for reading!