Transceiver enclosures

Transceiver enclosure

It has been a while since I finished the transceiver modules, and now I'd like to show some pictures of the process I used to put them into enclosures. I had some of these cast aluminum enclosures lying around, so they were pressed into service. They're a little on the heavy side, as the completed weight is around half a pound, but it's well within the carrying capacity of my Kadet. Before diving into the process of cutting the holes, I want to show some images of the transceiver board with the RFI fence installation process.

Cutting copper sheet

For use on the spectrum analyzer project, I found some sheet copper at the craft store. I think it was for etching, but I'm not totally sure, and I chose the thickest gauge they had. So far, the best way I've found to cut it is using an exact-o knife and a straight edge. I tried scissors, but it didn't really work.

RFI Fence

Once I had a strip of copper cut, I cut openings for the power and control traces and soldered it onto the PCB. I also soldered it onto the SMA connector. Once all that was finished, I soldered on a lid. Lots of solder flux helps here.

Once the board was prepared, both by soldering on a fence and replacing the pin header with a right-angle one, I began to prepare the enclosure. I was intending to drill a hole for the SMA connector, then cut a hole for the digital connection. The SMA connector hole was trivial to make, though the connector on the board was a little short. I ended up having to use an O-Ring from the hardware store (look in the plumbing section) to hold it in. When an antenna or cable is screwed on the O-Ring compresses, having the nice side-effect of sealing it.

DB-9 template

For the digital connection, I decided on using a DB-9 connector. I figured it was a prolific connector, so I should have lots of connectors laying around. But, that didn't turn out to be as helpful as I had hoped. To create nice holes for the DB-9 connectors I decided that I could use an old PCI bracket as a template. I lined the bracket up against the side of the enclosure and traced it. On the black box, I traced it using a knife, and on the grey box I used sharpie.

DB-9 template using sharpie

Once the outline was traced onto the box, I drilled holes for the retention screws. Then, I drilled out as much as I could of the trapezoid shaped interior. I mostly used the drill press, then the dremel with a router/cutter bit. I made sure to leave a margin inside the perimeter to remove with metal files. I had avoided purchasing a set of jewelers files for a while, I think I assumed that they were expensive. They're not, you should get a set.

Finished penetration

In the photo above, you can see the finished penetration for the DB-9. I beveled the inside edge to make room for the fillet on the connector that I had. The black box got a male DB-9, and the grey box got a female one. The holes need to be about the same size, as the male shroud always has to fit over the female connector body.

DB-9 connector installed

In addition to the RF and digital connectors, I needed a way to securely mount the internal circuit boards. The way I chose to do this was first to drill holes in the bottom of the box, then "countersink" some screws into it. I have countersink in quotes because I don't have a countersink bit, so I used a larger drill bit. You can see the results of this in the headline picture of this post. Though I think it looks pretty good, I still decided to buy a drill and tap set for 4-40 screws after building the black box. For the grey box, I used the tap and screwed directly into the box. This requires slightly less hardware and looks pretty good, I think.

Breadboard transceiver circuit

For whatever reason, the board I built for the black box (using some veroboard-style construction) didn't work the same as the breadboard. Because I was under time constraint (I was planning on flying one of the transceivers over the weekend). I decided to put it back on the breadboard and use it as the base-station. This version uses an FTDI cable to connect to my computer.

Flyable transceiver module

For the grey box, I used an extra ATMega48 breakout board I had. This one worked just fine in the enclosure, so I flew it. I also built a power regulation/distribution board, seen on the right of the photo.

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