N7DDC Auto tuner kit build - Up to 100W SSB
Browsing AliExpress.com, I came across this automatic antenna tuner kit designed by N7DDC. It was surprisingly cheap and I didn't mind waiting a month to receive it. I already have an MFJ automatic antenna tuner, and I wanted to build this one for portable/mobile/field operations. A good thing with this kit is that al SMD components were already soldered to the board. The construction part consists in soldering the thru-hole components, relays, making and installing the coils.
Before I started my build I did quite few searches online for information about the proper way of putting this kit together. Anyways, I had a month of waiting ahead of me for this to arrive!
I found many interesting ways to finish the kit, and even how to upgrade the software on the microcontroller to its latest version. However, the part I thought it would be good to learn with this kit, was the building the toroidal coils and measure them to ensure the have the correct inductance. Not needed, but I saw it in one of the videos.
In the photo is a little adapter board I made to connect the coil to the NanoVNA for measurement of inductance.
Is this very short video, an example measuring a coil with NanoVNA.
A close up to the screen inductance measurement.
All coils and first three relays installed
Everything installed on the board, rest of the relays and the thru-hole components
Smoke test with a 9V battery. It worked at the first attempt.
Solder pads for the two "optional" buttons for "Bypass" and "Auto"
This is on the bottom side of the board
Finishing the project aluminum box (an extra CAD$ 16 in Amazon.)
I've used regular SO239 chassis type connectors, instead of the SMA PCB type connectors that came with the kit.
Mounting the board on the box and soldering the connectors and buttons
Back of the unit
Front of the unit with OLED screen.
Bypass and Auto buttons are optional.
Tune button is mandatory.
Smoke test with my oldest radio. (Just in case you know.)
The tuner remembers only the last used setting (even after a power cycle), it doesn't remembers previous adjustments on each frequency tuned, like most automatic tuners do (internal or external.)