3D Printed Helical Satcom Feed

With the advent of cheap software defined radios made popular by the RTL-SDR project a few years back, satellite communications are now within the budget of even the most modest hacker. For $20 USD you can get a USB SDR module that is more than capable of receiving signals from any number of geosynchronous satellites, but you’ll need something a little more robust than rabbit ears to pick up a signal broadcast from over 22,000 miles away.

Building a satellite-capable antenna isn’t necessarily difficult, but does involve a fair bit of arcane black magic and mathematics to do properly; something that can scare away those new to the hobby. But by using a 3D printed mandrel, [Tysonpower] has come up with a feed you can build and mount on a standard dish without having to take a crash course in antenna theory. [Tysonpower] reports the feed has a center frequency 1550 MHz, and works well for reception of Inmarsat, AERO and HRPT signals.

The channel in the 3D printed core of the feed ensures that the inserted wire is of the correct length and in the perfect position for optimal reception. All you need to do is print the core, wrap it with wire, and then solder the end to a connector on a ground-plane that’s nothing more than a sheet of aluminum. [Tysonpower] was even kind enough to model up a mount that will allow you to bolt this feed to a standard satellite dish.

We’ve previously covered using RTL-SDR to receive Inmarsat transmissions, and hardware for the Outernet project, both of which would be great applications for an antenna like this.

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Sferics, Whistlers, and the Dawn Chorus: Listening to Earth Music on VLF

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.

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[Jeri] Builds a Magnetic Loop Antenna

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?

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Scratch That SDR!

When you think of a software defined radio, what language might you consider reaching for to create the software part of the equation? C? C++, maybe?

How about Scratch?

“What, Scratch as in the visual programming language aimed at young people?”, we hear you cry incredulously. It’s not exactly the answer you’d expect for an SDR, but thanks to [Andrew Back]’s work there is now ScratchRadio, a set of Scratch extensions for software defined radio. Why on earth do this? The aim is to lower the barrier to entry for software defined radio as far as possible, and to place it in a learning environment such as Scratch seems an ideal way to achieve that.

Of course, Scratch itself isn’t powerful enough for the heaviest of heavy lifting, so in reality this is a Scratch wrapper for a LuaRadio backend. It was created with the LimeSDR Mini in mind, but given that LuaRadio is not specific to that hardware we’d expect it to work with other SDRs such as the ever-popular RTL chipset TV sticks. It gives an owner of a Raspberry Pi 3 the ability to experiment with SDR coding without the need for a huge level of experience, and that to our mind can only be a good thing.

If you fancy trying ScratchRadio, you can find the code in its GitHub repository, and take it from there. Meanwhile we covered LuaRadio last year, so if Scratch is a little basic for you and GNU Radio too advanced, give it a try.

Radio icon: [Sakurambo], (CC BY-SA 3.0).

Scratch cat logo: MIT Media Lab.

LoRa Is the Network

We’ve become used to seeing LoRa appearing in projects on these pages, doing its job as a low-bandwidth wireless data link with a significant range. Usually these LoRa projects take the form of a client that talks to a central Internet connected node, allowing a remote wireless-connected device to connect through that node to the Internet.

It’s interesting then to see a modest application from [Mark C], a chat application designed to use a set of LoRa nodes as a peer-to-peer network. In effect LoRa becomes the network, instead of simply being a tool to access it. He optimistically describes peer-to-peer LoRa networks as the new FidoNet in his tip email to us, which might be a bold statement, but we can certainly see some parallel. It’s important to note that the application is merely a demonstrable proof-of-concept as it stands, however we’d agree that it has some potential.

The hardware used for the project is the Heltec ESP32-based LoRa board, which comes with a handy OLED screen on which the messages appear. As it stands a PC connection is required to provide text input via serial, however it’s not impossible to imagine other more stand-alone interfaces. If it interests you the code can be downloaded from the GitHub repository, so maybe this can become the seed for wider peer-to-peer LoRa networks.

There have been no shortage of LoRa projects featured here over the years. Recent ones include a handy local LoRa packet sniffer, and news of an extreme distance record from a LoRa node on a balloon.

3D Printed Dashboard CB Mount is Convoy Ready

Some may be surprised to hear that CB radio is alive and well in the 21st century. From disaster response to operating in areas without reliable communication infrastructure, there are plenty of reasons people are still reaching for their radio and not their smartphone. Unfortunately, modern automotive interior design doesn’t have such an enlightened view. It’s hard enough to get decent cup holders in some cars, let alone a spot to hang your microphone.

When presented with this problem in his Subaru Forester, [Alex Loizou] did what any modern hacker would, he 3D printed a mount that snaps into the stock dash. No drilling was required to attach his radio mount, it simply replaces a decorative trim piece that wasn’t doing anything anyway. Obviously this particular mount would only really work on the same year and make of vehicle as [Alex] has, but this is a good demonstration of how 3D printing can be used to adapt to existing hardware.

As is often the case when trying to print something to match perfectly with an existing object, there was a fair amount of trial and error required. It took a few attempts before [Alex] got the proper shape, and things weren’t made any easier by the fact he was doing his designing in TinkerCAD. While we appreciate the fact that TinkerCAD provides a web-based CAD tool that is easy enough for anyone to use, using a parametric design tool like OpenSCAD is generally preferred when you need to make slight adjustments to your model.

Software limitations aside, [Alex] managed to come up with a mount that not only holds his CB microphone, but also his handheld transmitter. All while looking about as close to stock hardware as something like this could. We especially like that he switched to a darker filament color for his final version to blend it into the dashes color scheme a bit better.

If your radio interest is a little full-fat for CB, take a look at what keeps ham radio alive and well in 2017, and if you’re a radio amateur with a hankering for the CB days we’ve got you covered.

Snazzy Balun Lets Ham Use Off-The-Shelf Coax

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.

[via r/amateurradio]