I considered a number of A.T.U. designs ranging from manual tuners to auto-tuning units and had a preference for building one of my own. In the end I came across this kit and at the price found it very compelling. Equipment requirements for this sort of operation are small size, low weight, battery powered and physically fairly rugged and this kit ticks all of those boxes. The tuner itself is available pre-built and tested for a very modest price but I wanted some stake in the project so I opted to build and test it myself.
The kit comes with two double-sided printed circuit boards and all wire, components and hardware necessary to built a complete unit, including the case and labeling. There are not a great number of components to deal with and the exception of one PIC micro-controller they're all discrete.
A full and accurate inventory is included, as are a couple of minor errata. This kit came with precisely the correct number of parts and enough wire to allow you a couple of mistakes.
A special note for the assembly and testing instructions is justified here. The instructions for the kit are superb. They assume very little, including any great proficiency at soldering. For an experienced builder they at first seem a little tedious with one whole page dedicated to soldering two BNC connectors but I soon learned that the instructions are filled with very insightful hints that are really worth following. It's obvious to me now, having finished the unit, that the instructions have been written with considerable experience of this kit. I was soon able to skim the page and tease out the juicy tender insight and to enjoy the rest for what they are.
The main board has some surface-mount components. In the kit I received they came pre-soldered. The main board is where most of the circuit for the tuning unit resides including the micro-controller, the relays and the various toroidal inductors and capacitors that comprise the tuning unit itself.
There were a couple of small challenges in construction of the Main Board. Some of the solder pads are quite close together, so you need a steady hand to avoid solder bridges in a couple of places, nothing that some solder wick won't help you correct if you make a mistake though. It's surprisingly fiddly fitting the single turn winding on the toroidal transformers. They look simple enough, but the board is very compact and there isn't a lot of wiggle room.
The Main Board immediately prior to the toroid-winding stage. Nearly all of the components have been added. The green boxes are the locking relays.
The first toroidal transformer almost ready for installation.
The two completed toroidal transformers installed.
The completed Main Board with all of the toroidal inductors installed.
The Control Board accommodates the external switches, LED's and connection to the internal battery. It plugs into the inline plugs on the Main Board.
Construction of the Control Board is very straightforward.
The completed Control Board.
Final assembly involves plugging the Control Board into the Main Board, installing the battery clips into the case, installing the boards into the case, soldering the ground connector and battery terminals, screwing the case together and labeling.
Control Board mounted on Main Board.
Completed Unit, in its box and labelled.
Basic testing worked just fine. The unit powered up, the morse information display appeared to be working and satisfying relay clunks were heard when putting the unit into and out of bypass mode.
After sorting out some appropriate cables I tested the unit with my FT-817ND in the backyard with a 7 metre squid pole and a couple of counterpoise wires. I tested 80-10 metres successfully!
Tuning took a few seconds of relay clattering to accomplish but SWR was fine at both band ends and band-middle for each band.
I purchased the optional FT-817 control cable. This appeared not to work, but I suspect that is because it has made some assumption about the CAT data rate and I've modified it. I'll sort that out next.
If you're interested in building one of these kits for yourself, you can find it, and a bunch of other interesting looking kits at:
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