Surplus Syringes Make Satisfactory Tuner for Amateur Radio Experimentation

Amateur Radio as a hobby has a long history of encouraging experimentation using whatever one might have on hand. When [Tom Essenpreis] wanted to use his 14 MHz antenna outside of its designed frequency range, he knew he’d need an impedance matching circuit. The most common type is an L-Match circuit which uses a variable capacitor and a variable inductor to adjust the usable frequency range (resonance) of an antenna. While inefficient in some specific configurations, they excel at bridging the gap between the 50 ohm impedance of the radio and the unknown impedance of an antenna.

No doubt raiding his junk box for parts, [Tom] hacked together a variable capacitor and inductor using ferrite rods from AM radios, hot glue, magnet wire, copper tape, and some surplus 60ml syringes. You can see that he ground out the center of the plunger to make room for ferrite rods. Winding the outside of the syringe with magnet wire, the alignment of the ferrite can be adjusted via the plunger, changing the characteristics of the element to tune the circuit. [Tom] reports that he was able to make an on-air contact using his newly made tuner, and we’re sure he enjoyed putting his improvised equipment to use.

If Amateur Radio isn’t your thing, then maybe we can entice you with this syringe based rocket, syringe actuated 3D printed drill press, or vacuum syringe powered dragster. Have your own hack to share? By all means, submit it to the Tip Line!

#radiohacks #amateurradio #coppertape #ferrite #impedancematching #syringe #variablecapacitor #variableinductor

Make Your Own Variable Inductor

Inductors are not the most common component these days and variable ones seem even less common. However, with a ferrite rod and some 3D printing, [drjaynes] shows how to make your own variable inductor. You can see him show the device off in the video below.

The coil itself is just some wire, but the trick is moving the ferrite core in and out of the core. The first version used some very thick wire and produced an inductor that varied from 6 to 22 microhenrys. Switching to 22 gauge wire allowed more wire on the form. That pushed the value range to 2 to 12 millihenrys.

What can you do with an inductor? For this type of inductor, you are usually interested in resonating a capacitor either for an oscillator or a filter of some kind. You see big roller variable inductors in antenna matching circuits, but it is doubtful that these inductors would be suitable for transmitting unless it was with very low power.

There are many ways to measure inductance, especially so today. The video shows an LCR meter and network analyzer. But it is easy enough to use a simple LC oscillator and measure the output with a scope or use a grid dip oscillator if you happen to have one. In the vein of making things easier, though, we really wanted to see [drjaynes] build a coil winder if he plans to make many of these.

#3dprinterhacks #3dprinting #inductor #variableinductor