The circuit is fairly simple but construction a lot more difficult so this page will concentrate on that aspect.
Switch wiring: The electronics op-amp must be shielded from the rest of the tuner. Programming Arduinos is just much more fun.Ham Radio - Build your own L network antenna tuner
An antenna tuner adds or subtracts wire to the length of your antenna automatically to find the best match. In Adelaide Australia, they are available from Cookson Controls.
Then transmit at low power while tuning the capacitor for a dip in SWR. Obviously k3ng has skills, but his focus is amateur radio and not microcontroller programming. Lay the board on your work surface, with the feet down.
The largest voltage, other than across the coil, is likely to be across the input capacitor which is usually smaller to slightly bigger than at the output terminals. If the SWR meter is not included, 50 ohm coaxial cable should be used especially for the higher frequensies. Drill another hole two inches away from the first hole, toward the front of the board.
Do not use this tuner or any unshielded tuner with more than 100 watts. If you have a PL-259 on the output not recommended at all then there is no point getting big capacitors. The voltages in the above table are PEAK voltages not those necessary to produce the power listed.
Mount the PVC pipe upright in the middle of the wood, using the L brackets and wood screws. It is very easy to ruin a variable capacitor if you are not used to handling them, because the plates get bent easily. Peel and stick the rubber feet in the corners of the board, on the roughest side. Both these meters read slightly differently no matter how long the patch cord or whether the linear amplifier is in circuit or not between radio and tuner.
If it looks like and duck and quacks like a duck, its a duck. If you really can't get a good tune within 20 seconds, you have something wrong.
A tuner is only suitable to two types of antenna viz. Voltage separation for capacitors, and all other components, will not depend on the mode of operation ie. Air makes a much better dielectric.
BUT, the transmitter power controls will roll back power near 3.
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