There was a time when people like us might own a tube tester and even if you didn’t, you probably knew which drug store had a tube testing machine you could use for free. We aren’t sure that’s a testament to capitalistic ingenuity or an inditement of tube reliability — maybe both. As [Usagi] has been working on some tube-based projects, he decided he needed a tester so he built one. You can see the results in the video, below.
The tester only uses 24V, but for the projects he’s building, that’s close to the operation in the real circuits. He does have a traditional tube tester, but it uses 100s of volts which is a different operating regime.
The bulk of the circuit is creating the voltages required, including a 555 charge pump to generate around -10V. The tube is wired up in a particular configuration and the Arduino makes a few measurements while changing the operating bias conditions. The converter goes through a voltage divider so the maximum 24 volts won’t overload the Arduino.
Grabbing the data into a spreadsheet allowed some curve tracing which looked useful for matching. However, as [Usagi] points out, the tester is very specific to his application. He has plans to maybe make a more general-purpose tube tester.
One of the problems with a truly general-purpose tube tester is connecting to the different pinouts. Punched cards offered one answer. If you don’t remember tube testers in drug stores, you might find that TV repair, at one time, was a big business.
Every time we see a dispatch from [Mr. Carlson], we imagine it is being beamed from his orbital station packed full of vintage radio gear. We are certain the reality is more terrestrial, but if we were going to build an orbiting lab, it might look like [Carlson’s] shack. In his latest communique, he shares his progress working on a high-performance 3-6-9 receiving antenna design and you can see it in the video below.
Although the antenna isn’t done, it is already working and looks impressive. There’s a lot of wire, so this probably isn’t a condo-friendly solution. The name of the antenna derives from the three wires, one tuned for 3 MHz, one for 6 MHz, and the other for 9 MHz.
The mechanical construction is impressive, with springs and pulleys. The wire used is actually MIG welding wire which is cheap and durable. Supposedly, the antenna has already performed well with an average receiver, but we didn’t get to hear it ourselves. Maybe in the next video.
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.
Dipoles are a classic builder’s antenna, after all they are usually little more than two pieces of wire and a feedline. But as [Rob] shows us in the video below, there are a few things to consider.
The first thing is where to get the wire. A damaged extension cord donated the wire. That’s actually an interesting idea because you get multiple wires the same length inside the extension cord. Of course, it is easy to just pull the conductors out of the extension cord, but how do you feed it? A small balun converts the unbalanced feed line into a balanced connection for the antenna. Although the title says “free dipole” this balun is commercial and probably cost something unless you happen to already have one. However, building a balun isn’t all that tricky, either if you happen to have a ferrite toroid.
If you want to transmit, you’ll probably need a little different arrangement, but for receiving this will definitely get the job done. A tuner would make life easier.
Even though this is technically a dipole, without tuning it is more of a random wire. However, it works and with antenna analyzers now common gear, it would be easy to shorten the dipole down to any band you wanted.
We don’t normally embrace the supernatural here at Hackaday, but when the topic turns to the radio frequency world, Arthur C. Clarke’s maxim about sufficiently advanced technology being akin to magic pretty much works for us. In the RF realm, the rules of electricity, at least the basic ones, don’t seem to apply, or if they do apply, it’s often with a, “Yeah, but…” caveat that’s sometimes hard to get one’s head around.
Perhaps nowhere does the RF world seem more magical than in antenna design. Sure, an antenna can be as simple as a straight piece or two of wire, but even in their simplest embodiments, antennas belie a complexity that can really be daunting to newbie and vet alike. That’s why we were happy to recently host Karen Rucker’s Introduction to Antenna Basics course as part of Hackaday U.
The class was held over a five-week period starting back in May, and we’ve just posted the edited videos for everyone to enjoy. The class is lead by Karen Rucker, an RF engineer specializing in antenna designs for spacecraft who clearly knows her business. I’ve watched the first video of the series and so far and really enjoy Karen’s style and the material she has chosen to highlight; just the bit about antenna polarization and why circular polarization makes sense for space communications was really useful. I’m keen to dig into the rest of the series playlist soon.
The 2021 session of Hackaday U may be wrapped up now, but fear not — there’s plenty of material available to look over and learn from. Head over to the course list on Hackaday.io, pick something that strikes your fancy, and let the learning begin!
AM radios are relatively simple devices, and building one is a good way to start exploring the world of radio communications. [GreatScott] does exactly this in the video after the break, building both a transmitter and receiver.
At the most basic level, AM radio works by generating a carrier wave with an oscillator, and then modulating the amplitude with an audio signal. Around these parts, the venerable 555 timer is always brought up whenever things get to oscillating; so you’ll no doubt be happy to see [GreatScott] decided to give it a shot for his first experiments, testing two popular 555 transmitter circuits. One uses the control voltage pin to input the audio signal, while the other uses the reset pin. The CV-pin version worked slightly better, but it was still just barely possible to distinguish a voice over a standard commercial AM/FM receiver.
The next attempt was with a XR2206 function generator kit, which worked quite well when combined with a simple microphone amplifier circuit. But this time the receiving side was swapped out, as [GreatScott] built a basic circuit around a TA7642 AM amplifier/demodulator IC, with only six passive components and a hand-wound coil.
Everybody has a bucket list, things to be accomplished before the day we eventually wake up on the wrong side of the grass. Many bucket-list items are far more aspirational than realistic; very few of us with “A trip to space” on our lists are going to live to see that fulfilled. And even the more realistic goals, like the trip to Antarctica that’s been on my list for ages, become less and less likely as your life circumstances change — my wife hates the cold.
Luckily, instead of going to Antarctica by myself — and really, what fun would that be? — I’ve recently been getting some of the satisfaction of world travel through amateur radio. The last installment of “The $50 Ham” highlighted weak-signal digital modes using WSJT-X; in that article, I mentioned a little about the Weak Signal Propagation Reporter, or WSPR. It’s that mode that let me test what’s possible with very low-power transmissions, and allowed me to virtually visit six continents including Antarctica and Sweden-by-way-of-Alaska.
Whispers in the Noise
Ask a random amateur radio operator what’s on his or her mind at any given moment and chances are pretty good the answer will be, “How are the bands right now?” That’s shorthand for what the current state of the ionosphere is, which largely determines how well RF signals will bounce off the various layers of charged particles that wrap around the planet. These layers shift and move in diurnal cycles, and undergo longer-term cycles of strengthening and weakening that depend on the cycles of magnetic activity on the Sun.
Assessing the state of the ionosphere and finding out which bands have a path to which points on the globe used to be something that hams had to do by spinning the dial and listening for beacon stations. Beacons are stations that transmit a generally low-power signal from a fixed, know location on a regular schedule. If you can hear the beacon, chances are good that you’ve got a propagation path between you and the general area of the beacon on that frequency.
While beacons are useful, they have their limits. They depend on the kindness of strangers, who devote resources to running and maintaining the beacon station. Beacons are also subject to occasional maintenance outages, so not hearing a beacon you expect does not necessarily mean that you don’t have a path between two points. But perhaps the most limiting aspect of traditional beacons is that they operate on a pull model — you have to sit down at your radio and intentionally tune into the beacon’s frequency and decode what you hear — beacons almost always use continuous wave (CW) mode with Morse code. Add to that the fact that whatever you learn about the propagation paths available to you stays pretty much within your shack, and beacons have limited utility.
With those limitations in mind, Joe Taylor (K1JT) began working on a digital mode in 2008 specifically for exploring propagation paths. The protocol was dubbed WSPR, which of course everyone pronounces as “whisper,” which given its capabilities is an apt name indeed. WSPR is a digital mode that employs special digital signal processing algorithms to decode signals with a signal-to-noise ratio (SNR) of -28 dBm in a bandwidth of 2,500 Hz.
When transmitting, WSPR sends a compressed 50-bit message that encodes the station’s callsign, the grid location, and the transmitter power. The message is modulated using frequency-shift keying at a very low bit rate — less than 1.5 baud. This means an entire message with error correction takes almost two full minutes to send. Transmissions are synchronized by the WSPR software to begin one second into each even-numbered minute, making accurate time synchronization essential.
Propagation Made Visual
As cool as the WSPR protocol is, the magic of WSPR comes from the “R” part of its name: reporting. This is where WSPR closes the loop that traditional beacons leave open, since WSPR client software can be configured to log any WSPR signals received and decoded by a station to a central database. WSPRnet.org is the place where all the reports go; the site contains a searchable database of all “spots” reported as well as a map that shows current contacts by many, many stations.
The map on WSPRnet is admittedly a bit janky — it’s based on Google Maps, and an error dialog pops up every time you load a new view. There are other visualizations, though, but even with the issues, WSPRnet’s map is a great way to see what propagation paths may be available to you at the current time.
For example, I took a quick peek at the 20-m band just now and found that from my area, I’ve got solid paths to pretty much all of North America. More importantly, I can see that I have no paths into Europe or Asia, and very little to the south into Central and South America. But, by looking at what’s going on with paths on the east coast of the US, where the sun is currently setting and which are actively reaching several stations in and just offshore of Antarctica, I might have a path to the bottom of the planet coming up as the sun sets over me.
Doing My Part
As I mentioned in my first weak-signals article, I’ve currently got WSJT-X running on a Raspberry Pi 4 that I have dedicated to ham radio use. WSJT-X has a built-in WSPR mode, which makes it easy to switch back and forth between exploring possible propagation paths with WSPR and exploiting that information to make actual QSOs using FT8 or one of the other supported modes.
The beauty of using WSJT-X for WSPR work is that it’s basically completely automated. Depending on how you set it up, you can either be a dedicated WSPR receiving and reporting station, or you can choose to also transmit.
When I’m going to be in the shack / office, which is almost always, I set up WSJT-X to transmit on WSPR with a 20% duty cycle — that is, one out of every five two-minute blocks will be dedicated to transmitting. That way, I can do my part contributing to the WSPR map — there generally aren’t many WSPR beacons operating in my part of North Idaho, so I figure this is my way of pitching in. Plus, I get the occasional bonus of nabbing a cool contact, like the aforementioned hit on DP0GVN-1, a German research vessel parked off the coast of Antarctica that I reached on the 30-m band using just five watts.
Sweden, By Way of Alaska
As cool as it is to know you’ve made a solid contact over a path of about 10,000 km on less power than it takes to run an LED light bulb, there’s also a lot to be said for the unusual stations you receive when you leave your WSPR station running. Case in point: the other day I glanced up at WSJT-X and noticed a strange callsign, SA6BSS. After a while of looking at callsigns you get to know which general areas they come from, and I suspected this was a “rare DX” coming from Europe, which is really hard for me to hit with my antenna from the inland Pacific Northwest. A quick lookup on QRZ.com confirmed that SA6BSS is a ham named Mikael Dagman, based in southern Sweden — cool!
I quickly spun up the WSPRnet map and was surprised to see that Mikael’s station was reporting its position as coming from Alaska rather than Sweden. I zoomed in the map a little and found that the signal was coming from a grid hundreds of kilometers south of Unalaska Island in the Aleutians. What in the world would a Swedish ham be doing in the North Pacific in February?
I shot Mikael a quick email about the contact, and he confirmed that I had indeed received a correct position report from his WSPR station, currently floating around the world on a party balloon! Since he released the balloon on Feb 23, it has traveled at around 11,000 meters altitude from Sweden to the Middle East, across Asia, and over the Pacific to just off the coast of Oregon. There it took a hook and headed back out to sea; as I write this it’s heading roughly in the direction of Hawaii.
Mikael was kind enough to include a little information on the WSPR transmitter he included on his balloon, which is completely solar-powered and weighs in at only 2.6 grams. The spareness of his design is almost comical — it’s just a GPS module, an ATMega328, and an Si5351 for the transmitter. It’s a perfect example of what can be done on a budget, which is right in line with “The $50 Ham” concept. So naturally, building a lightweight, inexpensive WSPR beacon will be the basis of the next installment in this series.
If you are a ham radio operator, the idea of sending pictures and data over voice channels is nothing new. Hams have lots of techniques for doing that and — not so long ago — even most data transmissions were over phone lines. However, now everyone can get in on the game thanks to the cheap availability of software-defined radio. Several commercial shortwave broadcasters are sending encoded data including images and even entire web pages. You can find out more at the Swradiogram website. You can also find step-by-step instructions.
WINB in Pennsylvania and WRMI Florida both have shows that include interspersed data. To play along, you’ll need a decoder like Fldigi or TIVAR. If you don’t have sufficient radio gear, you can probably borrow some from the Internet.
On the face of it, this might seem to be just a geeky hobby, but we can’t help but think that in places where data is censored, radio might be a viable way to send information. Some forward error correction codes and perhaps encryption could be a way to have a data lifeline to those forbidden from free access to the Internet. After all, history is full of stories of secret radio receivers tuned to the BBC or some other radio outlet, or examples of secret messages in broadcasts, such as Radio Swan. If you know Morse code, you might even get a warning about your impending rescue.
The film is presented without narration, but from the Dutch title cards and the fact that it’s Philips, we gather that this factory of gigantic proportions was somewhere in the Netherlands. In any case, it looks like something right out of [Fritz Lang]’s Metropolis and turned the rawest of materials into finished consumer products.
Much of the film focuses on the making of vacuum tubes; the sheer physicality of the job is what really stands out here. The upper body strength that the glassblowers had to have boggles the mind. Check out the chops — and the soon-to-be very unfashionable mustache — on the glassblower at the 12:00 mark. And it wasn’t just the gents who had mad skills — the fine motor control needed for the delicate assembly of the innards of the tubes, which seems to be mostly staffed by women, is just as impressive. We were also surprised by the amount these manual crafts were assisted by automated systems.
Especially interesting is the section where they build the luidspreker. Without narration or captions, it’s a little hard to tell what’s going on, but it appears that they used an enormous press to form chips of Bakelite into sleek covers for the speakers, which themselves are super-chunky affairs made from scratch in the factory. We’re also treated to assembly of the radios, packaging of finished products, and a group of dockworkers who clearly didn’t read the “Fragile” labels pasted on the boxes.
One can’t help but wonder if these people had the slightest inkling of what was about to sweep over them and the rest of the world. And if they did, would they even begin to comprehend how much the very products that they were making would contribute to both the slaughter of the coming war as well as to the sparing of so many lives? Likely not, but the film is still an interesting glimpse into the creation of an industry, one that relied very much on craftsmanship to get it started.
Using circuit simulating software like SPICE can be a powerful tool for modeling the behavior of a circuit in the real world. On the other hand, it’s not always necessary to have all of the features of SPICE available all the time, and these programs tend to be quite expensive as well. To that end, [Wes Hileman] noticed an opportunity for a specific, quick method for performing impedance calculations using python without bulky, expensive software and came up with a program which he calls fastZ.
The software works on any network of passive components (resistors, capacitors, and inductors) and the user can specify parallel and series connections using special operators. Not only can the program calculate the combined impedance but it can perform frequency analysis at a specified frequency or graph the frequency response over a wide range of frequencies. It’s also running in python which makes it as simple as importing any other python package, and is also easy to implement in any other python program compared to building a simulation and hoping for the best.
If you find yourself regularly drawing Bode plots or trying to cobble together a circuit simulation to work with your python code, this sort of solution is a great way to save a lot of headache. It is possible to get the a piece of software like SPICE to to work together with other python programs though, often with some pretty interesting results.