Building another ATU-100

 

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 carying 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.

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 power to tune to 1 Watt. Like in the previous build, I also removed three strands fromt he RG-58 inner conductor, 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 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 hey ... I had a nice screen ! (the LCD has a few minor faults 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. 

These are the further settings I made in the EEPROM:
NOTA: 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 by the antenna swaying in the wind).
One solution is to switch off the AUTO mode after tuning, or to change the 5th cell ( = cell 04) to 1.5 or so.
 

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 remain in the bag during use. So I started cutting pieces of  PCB, and started 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!  

This method reduces the number of holes to be drilled, and makes for a neat impression. 
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:

Seen from the back, these are the connections:

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 low 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