A Trail-Ready DSW-40

I would like to share a few impressions of the DSW-40 - from an "adventure radio" perspective - and offer some trail-friendly design suggestions for finishing your own DSW rig.

I won't go into all the details of the DSW-40 design. Excellent reviews of the DSW rigs are available in the July '99 QRP Quarterly and elsewhere. But I should mention a few features which make the DSW-40 particularly fit for "adventure" radio operation. At only 7 cm x 11 cm, the board is sufficiently small - an important consideration for backpacking . With low current consumption (~ 32 mA on receive), and the ability to continue to perform at reduced supply voltage, the DSW should "keep on going" long after other rigs will have given up. The nominal 2.5 W output at 13.8 v dc is a good power vs. battery requirement compromise for backpacking. And two features that I know I will especially appreciate in a tent after sundown are the frequency annunciation in cw (activated by depressing the encoder tuning control), and the calling-frequency initialization on power-up.

You may ask why I chose the 40 m DSW. One reason was that it was the only model available at the time. However, even though 20 and 30 m models are available now, I suspect that my DSW-40 will be ideally suited for multi-day canoe trips, where antennas don't go up until the tent is pitched and the evening meal is prepared.

Also unavailable when I bought the DSW-40 was the custom enclosure. This didn't bother me, as I had already selected a die-cast aluminum box for the purpose from the junk box. (Ontario hams will correctly suspect that this box came from VE3HC, Fred Hammond of Hammond Manufacturing fame, who every year brought a large supply of project boxes to the Central Ontario Hamfest.) The box is Hammond #1590BB, and measures 4.67"x3.68"x1.33" . It is available wherever Hammond enclosures are sold, unfortunately at a higher cost than the 50 cents Fred charged me !) In exchange for a few extra ounces of backpack weight, I felt this enclosure would provide an added degree of trail ruggedness, in a package that is about the same volume as the stock enclosure.

Unlike a clamshell case, where controls and jacks must be mounted on the "front" or the "back", the diecast enclosure would permit mounting on all four sides, as ergonomic considerations and personal preference dictated. Creative trail-friendly radio designs illustrate that the ideal arrangement of controls is NOT the same when operating in a sleeping bag or on a cliff as it is when operating in the home shack. My own preference is to avoid rear-mounted jacks, so the radio can be "angled" (resting on a branch, a rock, or clothing) with all controls and connections visible to the operator. My chosen configuration is shown in fig. 1. The tuning control (encoder) is located near the center of the front face, with the gain control to the left. The keyer configuration pushbutton and RIT toggle are to the right of the tuning control, and the paddle jack is at the far right of the front face. The dc jack and BNC antenna jack are on the right side , and the earphone jack is near the front face on the left side (i.e. opposite the dc connector visible in fig. 1). As a right-handed operator, this arrangement assures that earphone wires and paddle wires won't get tangled. Side mounting of the antenna, dc, and earphone jacks provide convenient access, while minimizing clutter on the front face. Front mounting of the keyer jack was essential, to permit the use of a trail friendly paddle which I will describe shortly.

As you may have already guessed, the DSW board is mounted "sleeping bat" style, on the "top" of the aluminum enclosure, with all controls and jacks sitting "below" the board. This can be a bit confusing when laying out the arrangement of the controls, since the "right side" will become the "left side" when the radio is turned over and mounted on the shallow lid of the diecast enclosure. For example, the RIT toggle switch must be "on" in the down position when the rig is being assembled. The internal arrangement of the board and off-board components is shown in fig. 2. The board is positioned as far back as possible, to provide maximum clearance for the front-mounted components. Flat head screws were countersunk in the top (or is that the bottom?) of the enclosure.

Mount the board before marking any holes for drilling, to assure that you will have sufficient clearance for all off-board components (you will note that the side mounted jacks are not vertically centered, for this reason). Also, unused tabs on the dc jack and RIT switch are cut off to maximize clearance. Although the arrangement in fig.2 may appear "cramped", there is sufficient clearance to permit removal the board simply by desoldering the antenna jack center conductor and unscrewing the dc jack.

To complement my newly completed rig, I wanted a small set of paddles that I could connect directly to the paddle jack. We all know that paddle performance is directly proportional - while paddle trail-friendliness is inversely proportional - to the weight of the paddle base! So it makes sense to use the rig itself as an anchor for the paddles. Essential design criteria for my direct-connect paddles included light weight, minimal length from plug to paddle (to minimize torque wear-and-tear on the paddle jack), and alignment of the plug with the center of the paddles (to prevent the paddles from pivoting about the plug).

I had picked up a couple of sets of "Bulldog " mini-paddles after Dayton '99. One of these had been pressed into bicycle mobile service, and has performed well. So I decided to use the other set for my "direct-connect" paddles. To mount the Bulldog paddles to the stereo plug, a 1" x 5/8" piece of 1/4" Plexiglas is used. A 1/4" hole is drilled in the center of the Plexiglas, and the hole is then tapped with a 5/16" NF24 thread, which seems to be the closest standard to that used to secure the cover of a garden variety 3.5 mm stereo plug . Install the plug into the hole (you may have to use pliers to fully thread the plug on the base, but after doing this once it should be easy to install or remove the plug while completing the subsequent assembly steps), and note that the two "dit" and "dah" solder tabs protrude just beyond the surface of the Plexiglas, while the "common" tab is much longer.

Using side cutters, trim the common tab to the same height as the others, and make a small nick in it to facilitate mechanical connection of the paddle wire to the tab while soldering. Remove the plug from the Plexiglas base, and drill holes above and below the plug hole, for attachment of the paddles. Note that these holes must be very close to the plug hole, to assure that the wooden base of the bulldog paddles does not split. Drill starter holes into the wooden base of the Bulldog paddles, and temporarily screw the Plexiglas onto the paddles. Remove the paddles and reinstall the plug. Solder the three wires from the paddles to the plug tabs, keeping the wires as short as possible to minimize slack, and then bend over the tabs, flush against the Plexiglas (Before doing this, you may wish to use a dermal tool to make indentations in the Plexiglas where the bent tabs will rest. The base is then rescrewed onto the paddles, and the unit is complete, as shown in fig. 3.

The DSW-40 / paddle combo (fig. 4), along with a monoband inverted vee fed by RG-174 for best weight / loss compromise at 7 MHz, are now ready to hit the trail. You will notice that the installed paddles do not interfere with operation of the RIT or keyer control.

I am sure we will be hearing many DSW rigs in upcoming "to the field" events. Information on the DSW series is available at http://www.smallwonderlabs.com, and Bulldog paddle information can be found at http://www.qth.com/k9lu/Pic1.htm

See you on the trail!

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John Cummings, VE3JC, is a well known QRPer, outdoorsman, and writer of articles on low power radio.