In the last installment of “The $50 Ham” I built a common tool used by amateur radio operators who are doing any kind of tuning or testing of transmitters: a dummy load. That build resulted in “L’il Dummy”, a small dummy load intended for testing typical VHF-UHF handy talkie (HT) transceivers, screwing directly into the antenna jack on the radio.
As mentioned in the comments by some readers, L’il Dummy has little real utility. There’s actually not much call for a dummy load that screws right into an HT, and it was pointed out that a proper dummy load is commercially available on the cheap. I think the latter observation is missing the point of homebrewing specifically and the Hackaday ethos in general, but I will concede the former point. That’s why at the same time I was building L’il Dummy, I was building the bigger, somewhat more capable version described here: Big Dummy.
Continue reading “The $50 Ham: Dummy Loads, Part 2”
This is an exciting day for me — we finally get to build some ham radio gear! To me, building gear is the big attraction of amateur radio as a hobby. Sure, it’s cool to buy a radio, even a cheap one, and be able to hit a repeater that you think is unreachable. Or on the other end of the money spectrum, using a Yaesu or Kenwood HF rig with a linear amp and big beam antenna to work someone in Antartica must be pretty cool, too. But neither of those feats require much in the way of electronics knowledge or skill, and at the end of the day, that’s why I got into amateur radio in the first place — to learn more about electronics.
To get my homebrewer’s feet wet, I chose perhaps the simplest of ham radio projects: dummy loads. Every ham eventually needs a dummy load, which is basically a circuit that looks like an antenna to a transmitter but dissipates the energy as heat instead of radiating it an appreciable distance. They allow operators to test gear and make adjustments while staying legal on emission. Al Williams covered the basics of dummy loads a few years back in case you need a little more background.
We’ll be building two dummy loads: a lower-power one specifically for my handy talkies (HTs) will be the subject of this article, while a bigger, oil-filled “cantenna” load for use with higher power transmitters will follow. Neither of my designs is original, of course; borrowing circuits from other hams is expected, after all. But I did put my own twist on each, and you should do the same thing. These builds are covered in depth on my Hackaday.io page, but join me below for the gist on a good one: the L’il Dummy.
Continue reading “The $50 Ham: Dummy Loads”
If you want to talk about antennas, the amateur radio community has you covered, with one glaring exception. Very low frequency and Extremely Low Frequency radio isn’t practiced very much, ultimately because it’s impractical and you simply can’t transmit much information when your carrier frequency is measured in tens of Hertz. There is more information on Extremely Low Frequency radio in Michael Crichton’s Sphere than there is in the normal parts of the Internet. Now there might be an easier way to play with VLF radiation, thanks to developers at the National Accelerator Laboratory. They’ve developed a piezoelectric transmitter for very long wavelengths.
Instead of pushing pixies through an antenna, this antenna uses a rod-shaped crystal of lithium niobate, a piezoelectric material. An AC voltage is applied to the rod makes it vibrate, and this triggers an oscillating electric current flow that’s emitted as VLF radiation. The key is that it’s these soundwaves bouncing around that define the resonant frequency, and the speed of sound in lithium niobate is a lot slower than the speed of light, but they’re translated into electric signals because of its piezoelectricity. For contrast, if this were a wire quarter-wave antenna it would be tens of kilometers long.
The application for this sort of antenna is ideally for where regular radio doesn’t work. Radio doesn’t work underwater, but nuclear subs trail an antenna out of the back to receive messages using Extremely Low Frequency radio. A walkie talkie doesn’t work in a mine, and this could potentially be used there. There is a patent for this piezoelectric antenna, so if anyone knows of a source of lithium niobate, put a link in the comments.
We’ve seen this trick before to make small antennas even smaller, but this is the first time we’ve seen it used in the VLF band, where it’s arguably even more impressive.
Antennas come in many shapes and sizes, with a variety of characteristics making them more or less suitable for various applications. The average hacker with only a middling exposure to RF may be familiar with trace antennas, yagis and dipoles, but there’s a whole load more out there. [Eric Sorensen] is going down the path less travelled, undertaking the build of a self-tuning magnetic loop antenna.
[Eric]’s build is designed to operate at 100W on the 20 meter band, and this influences the specifications of the antenna. Particularly critical in the magnetic loop design is the voltage across the tuning capacitor; in this design, it comes out at approximately 4 kilovolts. This necessitates the careful choice of parts that can handle these voltages. In this case, a vacuum variable capacitor is used, rated to a peak current of 57 amps and a peak voltage of 5 kilovolts.
The magnetic loop design leads to antenna which is tuned to a very narrow frequency range, giving good selectivity. However, it also requires retuning quite often in order to stay on-band. [Eric] is implementing a self-tuning system to solve this, with a controller using a motor to actuate the tuning capacitor to maintain the antenna at its proper operating point.
If you’re unfamiliar with magnetic loop builds, [Eric]’s project serves as a great introduction to both the electrical and mechanical considerations inherent in such a design. We’ve seen even more obscure designs though – like these antennas applied with advanced spray techniques.
Watch Justin McAllister’s presentation on simple antennas suitable for a zombie apocalypse and two things will happen: you’ll be reminded that everything antennas do is amazing, and their reputation for being a black magic art will fade dramatically. Justin really knows his stuff; there is no dangle-a-wire-and-hope-for-the-best in his examples. He demonstrates that it’s possible to communicate over remarkable distances with nothing more than an off-the-shelf radio, battery pack, and an antenna of simple design.
Continue reading “Justin McAllister’s Simple, Post-Apocalypse-Friendly Antennas”
Ham radio isn’t just one hobby. It is a bunch of hobbies ranging from chatting to building things, bouncing signals off the moon, and lots of things in between. Some of these specialties, such as supporting disaster relief or putting odd locations “on the air”, require portable operation. To encourage disaster readiness, hams participate in Field Days which is a type of contest that encourages simulated emergency conditions. So how do you erect an antenna when you just have a few hours to set up a temporary station? [KB9VBR] shows how he and his friend used a Chameleon Emcomm III portable HF antenna for Winter Field Day. You can see the video review, below.
Unlike some portable antennas, this one is almost 100 feet of wire (73 feet of radiator and a 25 foot counterpoise). The entire affair is meant to be put up and taken down repeatedly.
Continue reading “Portable Ham Antenna Gets A Workout”
Not long ago, we published an article about researchers adding sensor data to passive RFID tags, and a comment from a reader turned our heads to a consumer/maker version which anyone can start using right away (PDF). If you’re catching up, passive RFID technology is behind the key fobs and stickers which don’t need power, just proximity to the reader’s antenna. This is a much “hackier” version that works with discrete signals instead of analog ones. It will not however require writing a new library and programming new tags from the ground up just for the user to get started, so there is that trade-off. Sparkfun offers a UHF reader which can simultaneously monitor 25 of the UHF tags shown in this paper.
To construct one of these enhanced tags, the antenna trace is broken and then routed through a switching device such as a glass-break sensor, temperature limit switch, doorbell, or light sensor. Whenever continuity is restored the tag will happily send back its pre-programmed data, and the reader will acknowledge that somewhere one of the tags is seeing some activity. Nothing says this could not be applied to inexpensive RFID readers should you just want a temperature warning for your gecko terrarium or light sensor to your greenhouse‘s sealed controller.
Thank you, [Mike Massen], for your tip on RFID Doing More Than ID.
Continue reading “Long-Range RFID With Feedback”