ATU
Some years ago I was given some bits and pieces of a couple of old rollercoaster coils. There were a couple of coil formers, shafts, nobs and the counter mechanisms. Unfortunately the frames they would have originally been built into were absent. Never the less I thought it would be a good starting point to build an ATU from. Using some 10mm thick kitchen chopping board material I set about building a frame, winding the coil and putting the parts together to complete one rollercoaster from all the bits.
Once I had a working rollercoaster I then set about building case large enough for it, two capacitors and the rest of the parts needed. An old computer case was cut up and fashioned into a box with a removable lid. I wanted the ATU to handle at least 100 watts so the case had to be large enough for some reasonably big capacitors.
Holes are marked out ready for the power and SWR meters, then a series of small holes around the inside of the marking out is made.
With a pair of small pointed tin snips I cut between the holes, removing the unwanted metal.
Finally finishing off with a file to the line of the marking out.
Proceeding in this manner with any square holes that need to be made can usually produced a reasonable finish.
For round holes I use a stepped cone drill, enabling the drilling of the different sized holes in the back panel for aerial sockets and switch shafts.
In the picture to the right can be seen the balun secured to the back panel for a balanced feeder option.
Using an old copper computer heat sink, some brass tube, thin doubled sided PCB material and some plastic, I attempted to make a capacitor. This proved to be a lot harder than I thought it would be.
The finished capacitor worked but was far short of 350pf that I was hoping for.
The vanes were further appart than they perhaps needed to be, but it was difficult getting the alignment to stay true, and the vanes not touching when turning.
I think if I have the time, another attempt at this is needed.
Using some well known graphics software I designed the front panel and then printed it out on my inkjet printer.
The final panel design after printing was then laminated, cut out and fixed to the front panel with thin double sided tape.
Using a scalpel blade, the holes could then be cut out around holes in front panel using the holes already in the metal work as a guide.
ATU almost finished apart from from some finishing off on the case and some small tweaks in side.