We live in an electromagnetic soup, bombarded by wavelengths from DC to daylight and beyond. A lot of it is of our own making, especially further up the spectrum where wavelengths are short enough for the bandwidth needed for things like WiFi and cell phones. But long before humans figured out how to make their own electromagnetic ripples, the Earth was singing songs at the low end of the spectrum. The very low frequency (VLF) band abounds with interesting natural emissions, and listening to these Earth sounds can be quite a treat.
Most new hams quickly learn that the high-frequency bands are where the action is, and getting on the air somewhere between 40- and 160-meters is the way to make those coveted globe-hopping contacts. Trouble is, the easiest antennas to build — horizontal center-fed dipoles — start to claim a lot of real estate at these wavelengths.
So hacker of note and dedicated amateur radio operator [Jeri Ellsworth (AI6TK)] has started a video series devoted to building a magnetic loop antenna for the 160- and 80-meter bands. The first video, included after the break, is an overview of the rationale behind a magnetic loop. It’s not just the length of the dipole that makes them difficult to deploy for these bands; as [Jeri] explains, propagation has a lot to do with dipole height too. [Jeri] covers most of the mechanical aspects of the antenna in the first installment; consuming a 50-foot coil of 3/4″ copper tubing means it won’t be a cheap build, but we’re really looking forward to seeing how it turns out.
We were sorry to hear that castAR, the augmented reality company that [Jeri] co-founded, shut its doors back in June. But if that means we get more great projects like this and guided tours of cool museums to boot, maybe [Jeri]’s loss is our gain?
It’s a dilemma many hams face: it’s easy to find yourself with a big spool of RG-11 coax cable, usually after a big cable TV wiring project. It can be tempting to use it in antenna projects, but the characteristic impedance of RG-11 is 75 Ω, whereas the ham world is geared to 50 Ω. Not willing to waste a bounty of free coax, one ham built a custom 1:1 current balun for a 75 Ω dipole.
Converting between balanced and unbalanced signals is the job of a balun, and it’s where the device derives its name. For hams, baluns are particularly useful to connect a dipole antenna, which is naturally balanced, to an unbalanced coax feedline. The balun [NV2K] built is a bifilar 1:1 design, with two parallel wires wound onto a ferrite core. To tweak the characteristic impedance to the 75 Ω needed for his antenna and feedline, [NV2K] added short lengths of Teflon insulation to one of the conductors, which is as fussy a bit of work as we’ve seen in a while. We appreciate the careful winding of the choke and the care taken to make this both mechanically and electrically sound, and not letting that RG-11 go to waste is a plus.
With as much effort as hams put into antenna design, there’s a surprising dearth of Hackaday articles on the subject. We’ve talked a bit about the Yagi-Uda antenna, and we’ve showcased a cool magnetic loop antenna, but there’s precious little about the humble dipole.
In the first part of our series on in-band signaling, we discussed one of the most common and easily recognizable forms of audio control, familiar to anyone who has dialed a phone in the last fifty years – dual-tone multifrequency (DTMF) dialing. Our second installment will look at an in-band signaling method that far fewer people have heard, precisely because it was designed to be sub-audible — coded squelch systems for public service and other radio services. Continue reading “In-Band Signaling: Coded Squelch Systems”
“When all else fails, there’s ham radio.” With Hurricane Harvey just wrapping up, and Irma queued up to clobber Florida this weekend, hams are gearing up to pitch in with disaster communications for areas that won’t have any communications infrastructure left. And the perfect thing for the ham on the go is this ham shack in a box.
Go-boxes, as they are known, have been a staple of amateur radio field operations for as long as there have been hams. The go-box that [Fuzz (KC3JGB)] came up with is absolutely packed with goodies that would make it a perfect EmComm platform. The video tour below is all we have to go on, but we can see a tri-band transceiver, an RTL-SDR dongle and a Raspberry Pi with a TFT screen for tracking satellites. The Pi and SDR might also be part of a NOAA satellite receiver like the one [Fuzz] describes in a separate video; such a setup would be very valuable in natural disaster responses. Everything is powered by a 12-volt battery which can be charged from a small solar panel.
[Fuzz] is ready for action, and while we genuinely hope he and other hams won’t be needed in Florida, it doesn’t seem likely at this point. You can read more about the public service face of ham radio, or about an even more capable go-box.
Amateur radio operator [KE4FOX] wanted to build his own 2M fox hunt transmitter for use at conventions. It would be contained in a 1020 Pelican micro case and attached to a person who would walk around transmitting a signal, leaving the hams to track down the fox. The project uses a DRA818 VHF/UHF transceiver plugged into a low-pass filter combined with a hardware DTMF decoder, all controlled by an ATmega328P and powered by a 11.2 mAh battery.
[KE4FOX] also etched his own PCB, using the PCB toner transfer method, folding a sheet of transfer paper around the board to align both layers. Then he etched the board using cupric chloride. When assembling the board he realized he had made a terrible error, assuming the transceiver module’s pins went in the top layer when in fact they should have gone in the bottom layer. He solved this by soldering in the module in upside down.
He dropped the project into the 1020 and installed an SMA antenna. After he assembled the project he found out that the level shifter he used on the Arduino’s 5 V data didn’t work as expected and it was stuck at a single frequency. Something to work on for V2!
[thanks, that Kat!]
How do you like your Ham and Cheese sandwich? If you answered “I prefer it beefy”, look no further than [William Osman]’s Vin Diesel Ham and Cheese Sandwich! [Osman]’s blog tagline is “There’s science to do” but he is the first to admit this is science gone too far. When one of his followers, [Restroom Sounds], commented “Please sculpt a bust of [Vin Diesel] using laser cut cross-sections of laser sliced ham”, he just had to do it.
His friend [CameraManJohn] modeled the bust using Maya and [Osman] has provided links to download the files in case there’s the remote possibility that someone else wants to try this out. They picked the cheapest packs of sliced ham they could get from the supermarket — so technically, they did not actually laser slice the ham. For help with generating the slice outlines, they found the Slicer app for Autodesk’s Fusion 360 which did exactly what needed to be done. The app converts the 3D model into individual cross sections, similar to an MRI. It helps to measure the thickness of various samples of your raw material so that the Slicer output is not too stretched (or squished). The result is a set of numbered 2D drawings that can be sent to your laser cutter.
The rest of the video scores pretty high on the gross-o-meter, as [Osman] goes about laser cutting slices of ham (and a few slices of cheese), tasting laser cut ham (for Science, of course), and trying to prevent his computer from getting messed up. In the end, the sandwich actually turns out looking quite nice, although we will not comment on its taste. A pair of googly eyes adds character to the bust.
One problem is that the Slicer app does not optimise its results for efficient packing. with the smallest part occupying the same bounding box as the largest. This leads to a lot of wasted pieces of ham slices to be thrown away. [Bill] is still wondering what to do with his awesome sandwich, so if you have suggestions, chime in with your comments after you’ve seen the video linked below. If you know [Vin Diesel], let him know.
This isn’t [Osman]’s first adventure with crazy food hacks — here are a few tasty examples: a Toast-Bot that Butters For You (sometimes), a Laser-Cut Gingerbread Trailer Home, and a Pumpkin-Skinned BattleBot.