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Various ramblings – Electronics, radio, old computers, cars & other junk…

Monthly Archives: September 2011

Small Wonder Labs SW-40 Kit (Part 3)

With the case finished, there was only one thing left to do… Jam the radio in the case and make it work!

The digital dial kit and main board are secured to the case using brass stand offs (used for securing motherboards in PC cases), once cleaned up they solder rather nicely to the PCB cladding. The lid is secured in the same way. The rest of the boards in the case are secured using double sided tape, they seem fairly well supported and weigh so little that they shouldn’t come free any time soon.

In the photos you can see the main board, the digital dial and a few other additions I made to the radio:

– The most visible is a small LM317 circuit used to step down the 16.5v laptop switchmode PSU. 16.5v is a little high for most of the devices in the case, 14v is just within the maximum spec (and just inside the cut-off volatge for the LM317).

– Located just below the regulator is the RIT tuning module. This is built dead-bug style, with the CMOS logic mounted in a socket which is soldered on to some veroboard up-side-down.

– The final addon board in the pictures is a failed iambic keyer I built, it’s sitting in front of the RIT board. I had a go at troubleshooting it but caved and ordered a picokeyer chip that I plan to build in shortly.

With all that done, the radio just needed a few little finishing touches and it was up and running. I am very happy with the way that it turned out, it performs well and looks great!

The SW-40 kit can be purchased from theĀ Small Wonder Labs.

The digital dial kit can be purchased fromĀ Hendricks QRP Kits.

Multimeter Repair

My relatively new BK Precision multimeter got rained on, a leak in the roof on the deck soaked the table I was working on when some heavy overnight rain decided to come bucketing down. To say it was rained on is an understatement really, it must have been placed perfectly under a torrent of water that jammed more water into the meter than there was air.

Needless to say, I was rather pissed off. I pulled the battery cover off, and a large quantity of nasty looking brown water came pouring out. I proceeded to dismantle the meter, cleaning and drying all traces of water. I put it back together with a fresh battery, flicked the range switch around, and nothing…

Shit… So I pulled it apart again to have a better look at the board. It looked fine first time around, but under closer inspection I noticed that several of the tracks leading away from the positive battery snap solder joint were corroded away down to bare fibreglass board. I followed the trace until I found an undamaged section, scrubbed the green mask off the trace and installed a small piece of wire in the damaged sections place (small 30 gauge wire, what was used to fix mistakes on prototypes and the like ages back).

I plugged the battery back in and to my relief the multimeter was working!!

The meter still seems to perform as well as it did before, hopefully it stays that way. I can only assume that the tracks were damaged due to some sort of electrolysis effect. The meter was left in the on position and it had gone into auto-off mode but still using some power, a likely culprit. The corroded tracks started from the exposed copper vias through the board, eating into the copper underneath the green lacquer on the board. Bit of a shock that it happened so quickly!!

On a side note, while cleaning the meter I found a track underneath the screen that had been cut during manufacturing. What looks like a date code possibly points out that it was built in 2008. Is mine an early model? Interesting…

Small Wonder Labs SW-40 Kit (Part 2)

Being my first transceiver, I really wanted to make it my own (well, as much as I could with a kit…). I had seen many radios built into cases made from FR4 fibreglass PCB material, and thought I might have a go at doing my own.

Quite a simple process but it would have been much easier if I had access to a treadle shear. I cut the basic shapes on my table saw, allowing for a few millimeters to get the sizes accurate and remove any rough edges left by the saw. I then used wet/dry sandpaper to square up the edges and get all the sizes correct so the box fit together with no gaps.

The next step is to solder the case together. I made a jig with 3 90 degree angles in a corner shape, this helped me keep the box square as I soldered it.

Once that was done, I marked out where the holes for the screen and controls would go and I drilled/filed to shape. The final step was to clean the copper again and paint it with clear to prevent the copper from oxidising. Very happy with the results!

“100 Watt” Dummy Load

To align my SW-40 transceiver I needed to use a dummy load, something I didn’t yet have. The dummy load I bodged together in a hurry was 2 x 0.5 watt 100 ohm resistors in parallel on a BNC chasis connector. It worked, but got warm enough to discolour the resistors enough to make reading the values tricky.

I had used thick film power resistors in a previous project and thought maybe I could find something suitable for a dummy load. A quick look on RS components and I found a 100 watt 50 ohm resistor going for $20. Being thick film construction, I figured it would make a fairly good dummy load with no inductance and as a bonus it would be very easy to strap to a heatsink. A quick google confirmed this, it seems that this is a fairly popular way to build dummy loads.

Below are a few pictures of the dummy load I built. Very quick project, only took me around an hour to build. The case is recycled, in its previous life it was a VGA splitter/amplifier. I simply cut out some new end plates and bolted the heatsink on covering the holes left by the VGA connectors. The heatsink is also recycled, nabbed from an older server junked at work.

The resistor may have a high power rating, but to reach that you would need an almighty heatsink and forced cooling. The piddly heatsink I’m using might manage 20-30 watts for a fair while, more than enough for me though.

Small Wonder Labs SW-40 Kit (Part 1)

My first transceiver kit, a nice little radio with great instructions and is easy to build. I built this board over 2 nights, about 4-5 hours in total. While researching and ordering this kit I was still in the process of getting my foundation license, and not long after getting the kit in the mail I stumbled onto a small problem…

Foundation license holders are not allowed to operate homebrew transmitters…

I went ahead with the build, but until I got my standard license I was stuck using it as a receiver. All the more reason to upgrade!!