I have built an ATU-100 kit back in 2020, see my previous reports about the build here and some tests I did here.
This time, I built a second one for my friend Geert, ON5GL, who is a keen POTA activator.
He bought the Windcamp carrying bag for the IC-705 (e.g. this one from Ali Express).
It has some nice ORANGE details which make me jealous 😉
But it is not a backpack, so it would not suit me for SOTA.
He wanted a cheap autotuner that fits in one of the compartiments of the bag. We determined the maximum size to be 18 x 11 x 5 cm.
I ordered an ATU-100 kit and two square flange BNC connectors on Ali Express, for a total cost of only 27.21€. The rest of the stuff came from my junkbox. I can't think of a cheaper automatic tuner solution!
First I built the tuner kit, which gave one strange problem, read on ...
Mounting the coils and the relays went smoothly.
For the SWR bridge, even the thinnest wire that came with the kit was too thick, so I used some thinner wire (0.3 mm). I kept the standard 10:1 winding ratio, but I changed the minimum tuning power to 1 Watt (see EEPROM settings further on).
Like in the previous build, I also removed three strands from the RG-58 inner conductors, to make the wires fit the holes in the PCB. After a lot of fiddling, it looked like this:
Adding the rest of the components was no problem, but then came the first test ... nothing came up on the OLED display, huh ?
I have a PicKit3, so I started investigating the EEPROM values that control the type of display, and the display address. Whatever values I tried, still nothing!
I tested the OLED in an Arduino project, and there the OLED was fine. So what could be wrong ?
In the end , I connected a 1602 LCD display and changed the approriate EEPROM cells, and hey ... I had a nice screen ! (the LCD has a few artefacts which are not important here). The tuner seemed to work OK when connected to my home antenna. Here I tuned my 20m groundplane on the 17m band.
After a lot of searching and reading, I decided to try the older firmware (3.0) that is also in my own tuner, and this solved the OLED problem.
NOTE: you may have trouble with the tuner starting to tune in the middle of a QSO, which is very annoying. This happens sometimes if the SWR changes to a value above 1.3 (maybe because the antenna is swaying in the wind, etc).
OK, and then it was time to put it in a box.
This time, I wanted all connectors, controls and the display to be at the same side, so the tuner can stay in the bag during use. So I started cutting pieces of PCB, and began by making the front panel.
After a lot of measuring, drilling, filing and soldering, this is how the back of the. front panel looked:
Three pushbuttons are glued between two small strips of PCB, which are then soldered to the front panel. The OLED is held with 4 pieces of stiff wire, soldered to the front, and bent over to keep the display pressed against the front. Make sure to file off the pins, so they don't short out!
Two BNC connectors with square flanges are held with two bolts and nuts, which should suffice to keep them in place. I prefer the square flanges over the round BNC's, which tend to turn themselves loose after some time. A DC connector, and a small ON/OFF switch complete the front panel.
The front, before labeling, looked like this:
Then came the bottom, back, and two lower side panels, and I mounted the tuner inside like this:
A thin aluminium plate (10 x 28.5 cm) was bent into a U-shape to make a cover, it is fixed with 4 Parker screws to the two lower side plates. Here a view of the complete project before closing the lid.
For the closed box with labels, see top picture.
And here the tuner is in use in the Windcamp bag, with the IC-705 in the front, the ATU-100 tuner in the middle (a little hidden), and a 12V-7Ah SLAB in the back.
This SLAB is rather bulky, so the next improvement will be to make a lighter and SMALLER battery pack, so maybe an EFHW antenna can be stored in the remaining space.
Happy tinkering !
73 de Luc - ON7DQ