When we published a piece about an ADS-B antenna using a Coke can as a groundplane, Hackaday reader [2ftg] got in contact with us about something with a bit more… stature.
A monopole groundplane antenna is a single vertical conductor mounted on an insulator and rising up above a conductive groundplane. In radio terms the groundplane is supposed to look as something of a mirror, to provide a reflection of what would come from the other half of a dipole were there to be two conductors. You can use anything conductive as your monopole, a piece of wire, (in radio amateur humour) a piece of wet string, or even beer cans. “Beer cans?” you ask incredulously, expecting this to be another joke. Yes, beer cans, and [2ftg] has been good enough to supply us with a few examples. The first is a 57-foot stack of them welded together in the 1950s for use on the 80 metre band ( we suspect steel cans may have been more common than aluminum back then), the second is a more modest erection for the 2 metre band, and the final one consists of photographs only of an HF version that looks a little wavy and whose cans are a little less beery.
The reporting in the 1950s piece is rather cheesy, but does give a reasonable description of it requiring welding rods as reinforcement. It also gives evidence of the antenna’s effectiveness, showing that it could work the world. Hardly surprising, given that a decent monopole is a decent monopole no matter how many pints of ale you have dispatched in its making.
The Coke can ADSB can be seen in all its glory here, and if all this amateur radio business sounds interesting, here’s an introduction.
Beer cans picture: Visitor7 [CC BY-SA 3.0].
[Scott Tilley] was searching for radio signals from the Air Force’s top-secret ZUMA satellite. He found something that is — we think — much more interesting. He found NASA’s lost satellite called IMAGE. You are probably wondering why it is interesting that someone listening for one satellite found another one. You see, NASA declared IMAGE dead in 2005. It went silent unexpectedly and did not complete its mission to image the magnetosphere.
NASA did a failure review and concluded that in all likelihood a single event upset caused a power controller to trip. A single event upset, or SEU, is a radiation event and should have been automatically recovered. However, there was a design flaw that failed to report certain types of power controller failures, including this one.
The report mentioned that it might be possible to reset the controller at a specific time in 2007, but given that NASA thought the satellite was out of commission that either never occurred or didn’t work. However, something apparently woke the satellite up from its sleep.
[Scott] did a lot of number crunching to determine that the satellite’s spin rate had only decreased a little from its operational value and that the doppler data matched what he expected. [Scott] can’t read or command the telemetry, so he doesn’t know how healthy the satellite is, but it is at least operational to some degree. It’s really neat to see members of the team that worked on IMAGE leaving comments congratulating [Scott] on the find. They are working to get him data formatting information to see if more sense can be made of the incoming transmissions.
Who knew listening to satellites could be so exciting? If you want to build your own ground station, you might be interested in this antenna mount. If you need to know what’s overhead, this can help.
With the advent of low-cost software defined radio (SDR), anyone who’s interested can surf the airwaves from the FM band all the way up to the gigahertz frequencies used by geosynchronous satellites for about $20 USD. It’s difficult to overstate the impact this has had on the world of radio hacking. It used to be only the Wizened Ham Graybeards could command the airwaves from the front panels of their $1K+ radios, but now even those who identify as software hackers can get their foot in the door for a little more than the cost of a pizza.
But as many new SDR explorers find out, having a receiver is only half the battle: you need an antenna as well. A length of wire stuck in the antenna jack of your SDR will let you pick up some low hanging fruit, but if you’re looking to extend your range or get into the higher frequencies, your antenna needs to be carefully designed and constructed. But as [Akos Czermann] shows on his blog, that doesn’t mean it has to be expensive. He shows how you can construct a very capable ADS-B antenna out of little more than an empty soda can and a bit of wire.
He makes it clear that the idea of using an old soda can as an antenna is not new, another radio hacker who goes by the handle [abcd567] popularized their own version of the “cantenna” some time ago. But [Akos] has made some tweaks to the design to drive the bar even lower, which he has dubbed the “coketenna”.
The primary advantages of his design is that you no longer need to solder anything or even use any special connectors. In fact, you can assemble this antenna with nothing more than a pocket knife.
You start by cutting the can down to around 68 mm in length, and cutting an “X” into the bottom. Then strip a piece of coax, and push it through the X. The plastic-coated center conductor of the coax should emerge through the bottom of the can, while the braided copper insulation will bunch up on the other side. If you want to make it really fancy, [Akos] suggests cutting a plastic drink bottle in half and using that as a cover to keep water out of the “coketenna”.
How well does it work? He reports performance being very similar to his commercial ADS-B antenna which set him back $45 USD. Not bad for some parts of out the trash.
We’ve covered the math of creating an ADS-B antenna in the past if you’d like to know more about the science of how it all works. But if you just want an easy way of picking up some signals, this “coketenna” and an RTL-SDR dongle will get you started in no time.
When it comes to finding what direction a radio signal is coming from, the best and cheapest way to accomplish the task is usually a Yagi and getting dizzy. There are other methods, and at Shmoocon this last weekend, [Michael Ossmann] and [Schuyler St. Leger] demonstrated pseudo-doppler direction finding using cheap, off-the-shelf software defined radio hardware.
The hardware for this build is, of course, the HackRF, but this pseudo-doppler requires antenna switching. That means length-matched antennas, and switching antennas without interrupts or other CPU delays. This required an add-on board for the HackRF dubbed the Opera Cake. This board is effectively an eight-input antenna switcher using the state configurable timer found in the LPC43xx found on the HackRF.
The key technique for pseudo-doppler is basically switching between an array of antennas mounted in a circle. By switching through these antennas very, very quickly — on the order of hundreds of thousands of times per second — you can measure the Doppler shift of a transmitter.
However, teasing out a distinct signal from a bunch of antennas virtually whizzing about isn’t exactly easy. If you look at what the HackRF an Opera Cake receive on a waterfall display, you’ll find a big peak around where you expect, and copies of that signal trailing off, separated by whatever your antenna switching frequency is. This was initially a problem for [Schuyler] and [Ossmann]’s experiments. Spinning the antennas at 20 kHz meant there was only 20 kHz difference in these copies, resulting in a mess that can’t be decoded. The solution was to virtually spin these antennas much faster, resulting in more separation, and a clean signal.
There are significant challenges when it comes to finding the direction of modern radio targets. Internet of Things things sometimes have very short packet duration, modulation interferes with antenna rotation, and packet detection must maintain the phase. That said, is this technique actually able to find the direction of IoT garbage devices? Yes, the demo on stage was simply finding the direction of one of the wireless microphones for the talk. It mostly worked, but the guys have some ideas for the future that would make this technique work a little better. They’re going to try phase demodulation instead of only frequency-based demodulation. They’re also going to try asymmetric antenna arrays and pseudorandom antenna switching. With any luck, this is going to become an easy and cheap way to do pseudo-doppler direction finding, all enabled by a few dollars in hardware and a laser-cut jig to hold a few antennas.
We’ll admit that [3DSage] has a pretty standard design for a crystal radio. What we liked, though, was the 3D printed chassis with solderless connections. Of course, the working pieces aren’t 3D printed — you need an earphone, a diode, and some wire too. You can see the build and the finished product in the video below.
Winding the coil is going to take awhile, and the tuning is done with the coil and capacitance built into the tuning arrangement so you won’t have to find a variable capacitor for this build. There is a picture of the radio using a razor blade point contact with a pencil lead, so if you want to really scrimp on the diode, that works too, and you can see how at the end of the video.
We did like the use of cord ends from a sewing and craft supply store to serve as solderless springs. This would be a great item to print off a few dozen copies and use it for a school or youth group activity. You might want to pair it with an AM transmitter, though so the kids won’t be dismayed at what is playing on AM in most markets. [3DSage] uses a sink for ground — literally a kitchen sink. However, if you try this, make sure all the pipes are metal or you won’t get a good ground and you probably won’t pick up any stations.
We’d like to get some of those springs and make some other kind of starter projects with them like the kits many of us had as kids. This reminded us of the old foxhole radios, found during World War II.
Continue reading “A Modern Take on the Crystal Radio”
Pick a card, any card. [Andrew Quitmeyer] and [Madeline Schwartzman] make sure that any card you pick will match their NYC art installation. “Replantment” is an interactive art installation which invites guests to view full-size leaf
molds casts from around the world.
A receipt file with leaf images is kept out of range in this art installation. When a viewer selects one, and carries it to the viewing area, an RFID reader tells an Arduino which tag has been detected. Solid-state relays control two recycled clothing conveyors draped with clear curtains. The simple units used to be back-and-forth control but through dead-reckoning, they can present any leaf
mold cast front-and-center.
Clothing conveyors from the last century weren’t this smart before, and it begs the question about inventory automation in small businesses or businesses with limited space.
We haven’t seen much long-range RFID, probably because of cost. Ordinary tags have been read at a distance with this portable reader though, and NFC has been transmitted across a room, sort of.
Continue reading “Long-Range RFID Leaflets”
If you’ve played Valve’s masterpiece Portal, there’s probably plenty of details that stick in your mind even a decade after its release. The song at the end, GLaDOS, “The cake is a lie”, and so on. Part of the reason people are still talking about Portal after all these years is because of the imaginative world building that went into it. One of these little nuggets of creativity has stuck with [Alexander Isakov] long enough that it became his personal mission to bring it into the real world. No, it wasn’t the iconic “portal gun” or even one of the oft-quoted robotic turrets. It’s that little clock that plays a jingle when you first start the game.
Alright, so perhaps it isn’t the part of the game that we would be obsessed with turning into a real-life object. But for whatever reason, [Alexander] simply had to have that radio. Of course, being the 21st century and all his version isn’t actually a radio, it’s a Bluetooth speaker. Though he did go through the trouble of adding a fake display showing the same frequency as the one in-game was tuned to.
The model he created of the Portal radio in Fusion 360 is very well done, and available on MyMiniFactory for anyone who might wish to create their own Aperture Science-themed home decor. Though fair warning, due to its size it does consume around 1 kg of plastic for all of the printed parts.
For the internal Bluetooth speaker, [Alexander] used a model which he got for free after eating three packages of potato chips. That sounds about the best possible way to source your components, and if anyone knows other ways we can eat snack food and have electronics sent to our door, please let us know. Even if you don’t have the same eat-for-gear promotion running in your neck of the woods, it looks like adapting the model to a different speaker shouldn’t be too difficult. There’s certainly enough space inside, at least.
Over the years we’ve seen some very impressive Portal builds, going all the way back to the infamous levitating portal gun [Caleb Kraft] built in 2012. Yes, we’ve even seen somebody do the radio before. At this point it’s probably safe to say that Valve can add “Create cultural touchstone” to their one-sheet.
Continue reading “Recreating the Radio from Portal”