Antenna Tuner Update

 

Looks pretty dont it LOL. Well it does not work. Why you may ask, well, the IO expander which was meant to be able to output 5V and 20ma per pin, could not raise the skin off a custard. 1.2V out into an open load is all i could get out of it. I do not know why, schematic is correct, the voltage is correct and the reset line is pulled high, I can read and write to the IC over I2C and turn the pins on and off, they just never get anywhere near being 5V out. Anyway, I have redesigned the board using only the pins on the micro to control the relays, having bodged some wires into it to make sure it would work.

I also have another iteration in the pipeline, were I have added some switching of the capacitance to either the input or output sides for low z and high z loads and have also added swr meter circuitry. It might be months before i have that totally ready, I am going to spend a lot more time on the layout to get it right.

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Air Variable Caps Part 2

Air variable cap parts arrived a couple of weeks ago now. Have had this sitting on the bench for over a week, thought i should post about it. These are the panels, i separated them by cutting the tabs off on the bandsaw. If i ever make a second iteration, I will add in some drillings to make the tabs break off.

6 plates top and bottom give a minimum capacitance of 20pf.

Fully meshed they give a maximum capacitance of 133pf. Using the parts on hand, I have enough plates to build 2 capacitors that are 60 to 400pf or there about’s, being 15 plates top and bottom. Its just a matter of spending the time assembling them. There are some changes i would make if I was to do them again, like make the rod 5mm rather than 4mm, this would make it easier to mount a knob on and things like that. There is a spring front and rear to apply resistance to the movable plates so they hold their position. Other than that, it works.

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