Soft Landings: Ultra Light Foam Cases for QRP Radios
The ARS Sojourner
I finally decided to build my own custom cases. The following design is based on a case I made years ago for a pair of miniature binoculars. After I dropped the binoculars on a rock, and the original case failed to prevent an expensive trip to the repair shop, I came up with a case made from lightweight, closed cell foam and a nylon stuff sack. This case has served me and my binoculars well for 10 years.
The QRP version of this case adds 3/4 inch to the overall dimensions of the radio, which represents just about the smallest possible case. I've built cases for several radios, from the Small Wonder Labs DSW, to the Elecraft K2. They've worked out so well that I recently built a case for my new Elecraft K1, before completing the kit.
Here, I'll describe the case I built for the Wilderness Radio Sierra, which weighs 4.0 ounces. (The K2 case weighs 6.5 ounces, and the DSW case is 2.5 ounces.) Closed cell foam is used for low-cost sleeping pads, and is readily available at any outdoor shop. Because the cells are closed (non-porous), the foam is firm and light.
There are many brand names with various characteristics; for protective cases, you want stiff, tough foam that doesn't become brittle at low temperatures. Commonly, closed cell sleeping pads are 3/8 inch thick, about 22 inches wide, and from 40 to 72 inches long. A 72 inch pad provides enough material for several cases, depending on your radios.
Occasionally, 1/2 inch foam is available, but I've found the thinner stuff to offer plenty of protection with less bulk. You'll also need a good, sharp knife so that you can cut the foam cleanly.
Xacto-type hobby blades are best; avoid scissors because they leave an uneven edge that is difficult to glue. You'll also need a good contact cement. I uses Barges Cement, a glue used by cobblers to attach boot soles, but any good contact cement intended for plastic and rubber should do the job. You'll also need Duct tape to attach the lid, and optionally to reinforce the case.
The first step is to measure the outside, overall dimensions of your radio, including knobs and switches. These dimensions will be the inside dimensions of your case, because you want the radio to fit snugly. In the following discussion, I'll use top, bottom, back, left side, etc. to refer to the foam pieces that cover the corresponding panels on the radio. It helps to lay out the dimensions full size on paper, at least for your first case. That way, you can visualize the design and the way the pieces fit together. Or you can lay out directly on the foam with a marking pen. In either case, check the dimensions against the actual radio before cutting.
In my design, the bottom piece forms the foundation for the case, and the side and back panels are glued to it. Accordingly, I cut the bottom piece 3/8 inch larger than the Sierra on all sides. Since the Sierra's overall width and depth are 6-5/8 by 7-1/8 inches, I cut the bottom piece to 7-3/8 by 7-7/8 inches.
Make sure you include the width of the Sierra's plastic case latches in the overall width. In the case (no pun intended) of the K2, you should ignore the height of the screw heads that hold the radio's panels together. The foam gives enough to accommodate the screw heads. Refer to this drawing to see how the other pieces fit together.
To avoid confusion later, during assembly, I marked each panel as I cut it. The top piece is the same size as the bottom piece. The right and left side pieces are the same depth as the bottom panel, 7-7/8 inches, but since they'll fit inside the top and bottom panels, they need only be as high as the radio.
In the case of the Sierra, they're 2-7/8 inches high. The front and back pieces fit within the top, bottom, and side panels, so they are the same dimensions as the radio, 2-7/8 inches high by 6-5/8 inches wide. You could assemble the case at this point, but I prefer to provide more protection for the protruding knobs, connectors, and switches. I added smaller pieces of foam as spacers to the front and back panels of the case so that the radio's panels rest on the foam, protecting the knobs.
The Sierra's foam case has two spacers, each made of two layers of foam, glued to the back panel. This gives 3/4 inch of spacing to keep the antenna jack and rear panel switches from contacting the back panel of the case. I added three layers of foam to the front panel of the case to protect the main tuning knob, and the smaller knobs and switches.
This also provides extra protection for the fragile LCD display. To determine the dimensions for these spacer pieces, measure the spacing and position of the controls. I allowed plenty of room, since there's no need for the controls to be held snugly by the foam. This drawing shows the dimensions of all the foam panels, and here's a photo of all the foam pieces prior to assembly.
The first step in assembly is to glue the spacer pieces onto the front and back panels. Before gluing, hold the pieces together and check the fit against the radio. I started the actual gluing by applying cement to the mating surfaces of the spacer pieces. Try to keep the cement from getting onto surfaces that won't be glued.
This isn't critical, as fully cured contact cement will not stick to or mar the radio panels. Allow the contact cement to dry for the time specified on the container. This is generally to a slightly tacky state. Then press the pieces firmly together.
You must position each piece precisely before allowing the glue-coated surfaces to touch, because you won't be able to separate them without tearing the foam. Repeat the procedure to glue the spacers to the front and back panels. My next step was to glue the side panels to the left and right edges of the bottom piece. Then, I glued to the back panel to the bottom and side pieces.
Gluing the top panel to the sides and bottom complete the basic case. The front panel is not glued in place. Instead, I taped its bottom edge to the case with duct tape. To do this, place the radio in the case (make certain the contact cement is completely dry so that you don't get any on the radio).
Then press the front panel of the case into place against the radio. It should fit flush with the top, bottom, and sides of the foam case. Now, form a hinge by taping lengthwise along the bottom edge of the case and front panel. Press the tape firmly into place, then flip the front panel completely open and remove the radio.
Apply another piece of tape to the inside of the bottom and front panels, parallel to the first. I also added a piece of tape to the top edge of the front panel to act as a handle. This makes it easier to open the case. Here's a photo of the completed case. Optionally, you can duct tape the main seams of the case. I've found that the tape adds strength without adding much weight.
Another option is get a waterproof nylon stuff sack that is large enough to hold the case. This adds an extra layer of dust and waterproofing to the case, and also serves to keep the front panel (lid) securely closed. You can either sew a custom stuff sack (which I keep meaning to do), or take the completed case to an outdoor store and buy one large enough to hold the case.
The weights mentioned above include the stuff sack for each case. The result of your work is a very light but highly protective case. Have a look at this photo, which shows the DSW and K2 next to their cases. Also, here's a photo of my K2 and its case in the field. The blue foam case is at the top center of the photo, above my operating position.
This design won't protect the radio from sharp objects, twisting or bending, or heavy blows, but that's not a problem inside a pack. I generally pack the radio and its case in a backpack for transport in a vehicle. Another option would be to use a large, rigid case, such as a plastic food container, or a hard camera case, to protect the radio inside its foam case.
I've carried the K2 in a pack on several field trips, and the other cases have seen some field use as well. So far, the radios have been perfectly protected.
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Bruce Grubbs, N7CEE, a veteran QRPer, builder, outdoorsman and writer, is a a contributing editor to The ARS Sojourner. He lives in Flagstaff, AZ.
mail@brucegrubbs.com