Have you ever looked up a recipe online, and before you got to the ingredients, you had to scroll through somebody’s meandering life story? You just want to know how many cans of tomato paste to buy, but instead you’re reading about cozy winter nights at grandma’s house? Well, that’s where you are right now, friend. Except instead of wanting to know what goes in a lasagna, you just want to see the inside of some weirdo alternative medicine gadget. I get it, and wouldn’t blame you for skipping ahead, but I would be remiss to start this month’s teardown without a bit of explanation as to how it came into my possession.
So if you’ll indulge me for a moment, I’ll tell you a story about an exceptionally generous patron, and the incredible wealth of sham medical hokum that they have bestowed upon the Hackaday community…
Continue reading “Teardown: Analog Radionic Analyzer”
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!
The inside of classic radios holds wonders that the sterile chips and SMD components of today’s circuits can’t hold a candle to. Chunky resistors and capacitors, vacuum tubes with cathodes aglow, and seemingly free-form loops of wire forming inductors will all likely make an appearance. But the most fascinating bit of any old radio was connected to the tuning knob: the big variable capacitor with its interdigitating metal plates. Watching one at work, with its plates evenly and finely spaced, is still a joy to behold.
In an attempt to recapture a little of that magic, [Jeremy S. Cook] came up with this home-brew variable tuning capacitor. The frame is built mainly from 3D-printed parts, which supports a shaft made from a common bolt. Plates are fashioned from stainless steel fender washers cut in half; the fixed plates are press-fit into the frame while the rotary plates ride on the shaft. The spacing between the rotary plates is maintained by printed spacers, which also serve to lock the rotor into one solid unit. [Jeremy]’s prototype, for which he provides STL files, can be tuned between about 7 and 15 pF. Check out the build in the video below.
We love the look of this, and we can imagine custom tuning caps would come in handy for certain retro radio builds. The tuning range is a little narrow, but that could be fixed with more plates or closer spacing. That might be a tall order with thick steel washers, but we’ve seen really thin aluminum machined and closely spaced before, so this might be one approach to higher capacitance. Continue reading “DIY Tuning Capacitors From Washers And 3D-Printed Parts”
If you enjoy building radio projects you may have noticed something slightly worrying over the last few years in your component supply. Variable capacitors are no longer as plentiful as they used to be. There was a time when all radio receivers contained at least one, now with the advent of the varicap diode and the frequency synthesiser the traditional tuning capacitor is a rare breed. They are still made, but they’re not cheap and they won’t appear so readily in your junk box any more.
Fortunately a variable capacitor is a surprisingly simple device, and one you can make yourself if you are of a mind to do so. [Patrick] did just that with his home-made capacitor, in this case of a few tens of pF and suitable as a low-power trimmer capacitor or in a single-chip FM radio.
Rather than make a set of interlocking vanes as you’d find in a commercial design, he has gone for a screw in a tube. The capacitance is set by the length by which the screw is inserted into the tube. And his tube is not a tube in the traditional sense, instead he has used a coil of enamelled copper wire wound on the screw thread, whose insulation forms the dielectric. It looks wrong to use a coil in this way as you’d expect a similar coil to form the inductive part of a tuned circuit, but this coil is shorted out to prevent its inductance becoming a factor at the frequency in question.
It’s evidently not the answer to all variable capacitor problems, but it’s a neat piece of lateral thinking and it will make a simple working capacitor from readily available parts.
We’ve featured a couple of more traditional style home-made variable capacitors in the past on these pages, one made from thin aluminium sheet cut with scissors, and another one designed for use in higher power transmitters.
Thanks [PeterF] for the tip.
[Jezan] decided to introduce his son to electronics by building a small crystal radio. These crystal sets have been around for a long time, and make for a great beginner electronics project, but some of the required parts are a little hard to come by. The most difficult to source part for these radios is a variable capacitor, and not finding one in his parts bin, [Jezan] decided to make his own.
This variable capacitor comes directly from a piece of 1.5 mm thick aluminum sheet. Instead of fancy CNC machines, power tools, or even a pair of tin snips, [Jezan] cut the rotors and stators for his variable capacitors with a pair of scissors. The center hole was punched out with a piece of sharpened pipe, and all the pieces were filed down and sanded for a perfect finish.
Considering the variable caps you can get your hands on are either rare or very old, this looks like a great afternoon project for the budding electronics wizard or radio enthusiast. [Jezan]’s craftsmanship is incredible as well and the finished part looks like it came off an assembly line.
[Scott Harden] has been working through a design for a variable inductor to use as a PTO, or permeability tuned oscillator. What you see above is the most recent fruit of these efforts. The variable inductor is made up of the green coil of wire with a threaded bolt in the core. Turning that bolt moves the tip in or out of the coil, affecting its inductance.
Traditionally, tuning RF oscillator circuits has been a function of an adjustable capacitor. But capacitance is only part of the circuit, with inductance being the other important portion. Since variable capacitors that are capable of affecting a large change on the frequency of a circuit can be quite expensive he set out to find another way. This is what prompted the development of his first PTO project.
[Scott] produced a demo video of the hardware seen above which we’ve embedded after the break.
Continue reading “Experimenting With A Permeability Tuned Oscillator”