The handbook antenna tuner reveals how homebrewing is finished
If there is something in amateur radio that is more witchcraft than the design and implementation of antennas, we don’t know what it would be. At first glance, hanging up a piece of wire doesn’t seem complicated, but when you dive into the details it can be quite complex to build effective antennas and customize them for the job at hand.
Of course, that doesn’t mean antenna issues need to remain a mystery, especially when someone is taking the time to explain things properly. [Charlie Morris (ZL2CTM)] This was recently done with a simple antenna tuner, a device that is used to match impedances between a transmitter and an antenna. As he explains in the first video below, his tuner design is actually just a Wheatstone bridge with the antenna halfway up a leg. A toroidal transformer with several taps and a variable capacitor forms an LC circuit that corresponds to the high-impedance antenna, in this case an end-fed multi-band half-wave, with the nominal load of 50 ohms expected from the transceiver. A small gauge and diode detector will indicate when the bridge is balanced, which means the transceiver is seeing the correct load.
The second video below shows the final implementation of the tuner. as a fan of QRP or low-power operation, [Charlie] prefers simple, lightweight homebrew gear that can be easily brought into the field, and that definitely fits. A final video shows the tuner in use, with a NanoVNA proving what it can do. As usual, [Charlie] protests that he’s not an expert and just documents what he’s done, but he always does such a good job presenting the component selection calculations that any ham should be able to replicate their builds.