someguynamedross.com

Various ramblings - Electronics, radio, old computers, cars & other junk...

Radio

Random radio projects for the amateur bands. Finally sat my foundation license in late October, received my license on the 14th of November along with my callsign, VK3FPAA.

Now to study up for the Standard license so I can actually use home made gear!!

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 the Small Wonder Labs.

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

Small Wonder Labs SW-40 Kit (Part 2)

Being my first transceiver, I wanted to really 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. Turned out very well!

"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 100ohm resistors in parallel on a BNC chasis connector. It worked, but got a "bit" warm when exceeding the power rating of the resistors...

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 100watt 50ohm 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 like 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 maybe even 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 that is easy to build. I built this board over 2 nights, about 4-5 hours in total. While building 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!!

40m/7MHz Loaded Dipole

My first project for the radio section of my website, and a nice easy one at that! This is a loaded dipole for the 40m/7MHz band, this design was chosen mainly due to the fact I don't have enough room to hang a full size dipole. I created the design using a great calculator I found here. There are many great calculators on that website (I also used the air-core inductor calculator for this antenna), well worth bookmarking!!.

I punched in a maximum length of 7m into the calculator and started fiddling with the values until I got something useful. 7 meters happens to be the longest length on the roof where I can easily hang a dipole (relatively) straight. Saved me having to put up a tower/supports, and also meant it was very discrete and out of the way.

The antenna is very basic in its construction, made from .75mm enamled wire I pulled out of an old transformer. Loading coils are formed on 1" ID PVC pipe, and the center insulator holding the BNC connector and balun is a piece of plastic packaging I found in the bin in the garage. This is one very low cost antenna as pretty much all materials were recycled, even the bolts in the loading coils which recycled from the transformer I pulled apart. The only thing I purchased was the BNC connector.

Total time spent building and hanging it was probably around the 2 hour mark. While I was finishing the balun, I had the antenna strung up about half a meter off the ground. Thought I'd do some quick testing with my VR-500 receiver (not very good on HF...), and managed to listen in to a very clear SSB transmission from Tasmania (VK7), which is around 400km's from where I live in Victoria! Since hanging it up on the roof I've been able to listen in on several SSB transmissions, and plenty of CW too. Just need to learn morse code...