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How do you know that your patch cables are good? For simple jumper wires, a multimeter is about all you need to know for sure. But things can get weird in the RF world, in which case you might want to keep these coaxial patch cable testing tips in mind.

Of course, no matter how high the frequency, the basics still apply, and [FesZ] points out in the video below that you can still get a lot of mileage out of the Mark 1 eyeball and a simple DMM. Visual inspection of the cable and terminations can reveal a lot, as can continuity measurements on both the inner and outer conductors. Checking for shorts between conductors is important, too. But just because the cable reads good at DC doesn’t mean that problems aren’t still lurking. That’s when [FesZ] recommends breaking out a vector network analyzer like the NanoVNA. This tool will allow you to measure the cable’s attenuation and return loss parameters across the frequency range over which the cable will be used.

For stubborn problems, or just for funsies, there’s also time-domain reflectometry, which can be done with a pulse generator and an oscilloscope to characterize impedance discontinuities in the cable. We’ve covered simple TDR measurement techniques before, but [FesZ] showed a neat trick called time-domain transformation, which uses VNA data to visualize the impedance profile of the whole cable assembly, including its terminations.

There are many ways to build a radio receiver, but most have a few things in common, such as oscillators, tuned circuits, detectors, mixers, and amplifiers. Put those together in the right order and you’ve got a receiver ready to tune in whatever you want to listen to. But if you don’t really care about tuning and want to hear everything all at once, that greatly simplifies the job and leaves you with something like this homebrew all-band receiver.

Granted, dispensing with everything but a detector and an audio amplifier will seriously limit any receiver’s capabilities. But that wasn’t really a design concern for [Ido Roseman], who was in search of a simple and unobtrusive way to monitor air traffic control conversations while flying. True, there are commercially available radios that tune the aviation bands, and there are plenty of software-defined radio (SDR) options, but air travel authorities and fellow travelers alike may take a dim view of an antenna sticking out of a pocket.

So [Ido] did a little digging and found a dead-simple circuit that can receive signals from the medium-wave bands up into the VHF range without regard for modulation. The basic circuit is a Schottky diode detector between an antenna and a high-gain audio amplifier driving high-impedance headphones; [Ido] built a variation that also has an LM386 amplifier stage to allow the use of regular earbuds, which along with a simple 3D-printed case aids in the receiver’s stealth.

With only a short piece of wire as an antenna, reception is limited to nearby powerful transmitters, but that makes it suitable for getting at least the pilot side of ATC conversations. It works surprisingly well — [Ido] included a few clips that are perfectly understandable, even if the receiver also captured things like cell phones chirping and what sounds like random sferics. It seems like a fun circuit to play with, although with our luck we’d probably not try to take it on a plane.

If there’s anything more annoying to an amateur radio operator than noise, we’re not sure what it could be. We’re talking about radio frequency noise, of course, the random broadband emissions that threaten to make it almost impossible to work the bands and pick out weak signals. This man-made interference is known as “QRM” in ham parlance, and it has become almost intolerable of late, as poorly engineered switch-mode power supplies have become more common.

But hams love a technical challenge, so when a nasty case of QRM raised its ugly head, [Kevin Loughlin (KB9RLW)] fought back. With an unacceptable noise floor of S8, he went on a search for the guilty party, and in the simplest way possible — he started flipping circuit breakers. Sure, he could have pulled out something fancier like a TinySA spectrum analyzer, but with his HF rig on and blasting white noise, it was far easier to just work through the circuits one by one to narrow the source down. His noise problem went away with the living room breaker, which led to pulling plugs one by one until he located the culprit: a Roomba vacuum’s charging station.

Yes, this is a simple trick, but one that’s worth remembering as at least a first pass when QRM problems creep up. It probably won’t help if the source is coming from a neighbor’s house, but it’s a least worth a shot before going to more involved steps. As for remediation, [Kevin] opts to just unplug the Roomba when he wants to work the bands, but if you find that something like an Ethernet cable is causing your QRM issue, you might have to try different measures.

Although ham radio can be an engaging, rewarding hobby, it does have a certain reputation for being popular among those who would fit in well at gated Florida communities where the preferred mode of transportation is the golf cart. For radio manufacturers this can be a boon, as this group tends to have a lot of money and not demand many new features in their technology. But for those of us who skew a bit younger, there are a few radios with custom firmware available that can add a lot of extra capabilities.

The new firmware is developed by [NicSure] for the Tidradio TD-H3 and TD-H8 models and also includes a browser-based utility for flashing it to the radio without having to install any other utilities. Once installed, users of these handheld radios will get extras like an improved S-meter and detection and display of CTCSS tones for repeater usage. There’s also a programmer available that allows the radio’s memory channels to be programmed easily from a computer and a remote terminal of sorts that allows the radio to be operated from the computer.

One of the latest firmware upgrades also includes a feature called Ultra Graph which is a live display of the activity on a selected frequency viewable on a computer screen. With a radio like this and its upgraded firmware, a lot of the capabilities of radios that sell for hundreds of dollars more can be used on a much more inexpensive handheld. All of this is possible thanks to an on-board USB-C interface which is another feature surprisingly resisted by other manufacturers even just for charging the batteries.

Analog radio broadcasts are pretty simple, right? Tune into a given frequency on the AM or FM bands, and what you hear is what you get. Or at least, that used to be the way, before smart engineers started figuring out all kinds of sneaky ways for extra signals to hop on to mainstream broadcasts.

Subcarrier radio once felt like the secret backchannel of the airwaves. Long before Wi-Fi, streaming, and digital multiplexing, these hidden signals beamed anything from elevator music and stock tickers to specialized content for medical professionals. Tuning into your favorite FM stations, you’d never notice them—unless you had the right hardware and a bit of know-how.

Sub-what now?

Subcarrier radio was approved by the FCC under the Subsidiary Communications Authorization. This allowed both AM and FM radio stations to deliver additional content through subchannel broadcasting on their existing designated frequency. Practicalities mean that only FM stations could reasonably use this technique to broadcast additional audio content; AM radio stations were too limited in bandwidth to do so. In the latter case, only low-bitrate data could be sent on a subcarrier. 1983 saw the deregulation of subcarrier broadcasts, with existing broadcasters able to use them largely as they wished.

To understand how this let FM radios broadcast extra programming, we need to know how subcarriers work. Basically, in this context, a subcarrier is a high-frequency signal outside the range of human hearing—usually something like a sine wave at a frequency of 20 KHz to 100 KHz or so. This signal is then amplitude modulated with the desired secondary audio program for broadcast. As this signal is beyond the range of human hearing, it can be mixed with the regular station’s main audio feed without perceptibly altering it to any great degree. The mixed signal is then frequency modulated on to the radio station’s main carrier signal (usually in the range of 88-108 MHz) and sent up the tower for broadcast over radio.

For subchannel broadcasting, FM stations typically used subcarriers at 67 kHz or 92 kHz to carry additional low-fidelity mono audio feeds. These carrier frequencies were chosen to avoid the existing subcarrier signal in FM stereo broadcasts, which carried a left-right channel difference signal at 38 kHz.

Subcarriers were a neat little lifehack that let a single frequency do double or triple duty. A single FM station could deliver its main program, plus a bonus low-fidelity mono channel for various purposes. This facility was used for all kinds of obscure uses. Some broadcasters delivered background music for piping into department stores and the like, while others created special channels reserved for reading-for-the-blind organizations.

The Physician’s Radio Network was also a notable user, which broadcast information of specific relevance to medical professionals. However, the limited audience made it a difficult prospect to keep running from a commercial standpoint, even though it saved money by merely rebroadcasting one hour of programming around the clock on any given day. It eventually went off the air in 1981.

Tuning into these broadcasts wasn’t possible on a regular FM radio. Instead, you needed a device specifically built to pull the subcarrier signal out of the radio broadcast and then demodulate it back into listenable audio. By and large, organizations broadcasting on subchannels would distribute special radios that were tuned to only decode their sub-carrier station. The hardware involved wasn’t complex—it just involved demodulating the FM broadcast signal, then filtering out the subcarrier signal and demodulating that back into audio.

FM subcarriers weren’t just for audio, either. Microsoft famously used 67.7 kHz subcarriers on FM radio stations for its now-defunct DirectBand datacast network. It could deliver data at 12 kbit/second, or over 100 MB a day. The technology was used to deliver things like weather reports and stock prices to early smartwatches and coffee makers in the days before WiFi and celluar internet were cheap and everywhere.

From a hardware hacker’s perspective, these channels were a fun challenge to hunt down. With the right radio receiver and a bit of circuit hacking to tap off the baseband signal, you could decode the subcarrier and reveal the hidden broadcast. Some hobbyists rigged up surplus SCA receivers—often stuff found at flea markets or hamfests—to get free background music, weather reports, or any niche audio that happened to be riding along. Alternatively, decoding the subcarrier was entirely possible by building your own gear. It was kind of a neat analog puzzle—filter out the main audio, isolate the frequency where the secret channel lived, and then demodulate it. The hardware you’d use looked suspiciously like the guts of a standard FM radio, just with a few added filters and demodulation stages stuck in. These days, software defined radio techniques make doing the same thing comparatively easy.

Though it felt like eavesdropping, this wasn’t exactly some top-secret espionage. While technically unauthorized reception was frowned upon by the FCC, it wasn’t heavily policed. Subcarrier channels didn’t exactly have roving gangs of enforcers prowling about the neighborhood. Mostly, these subcarriers delivered paid subscription services, like Muzak, or nonprofit programming authorized under the station’s broadcast license. Their decline coincided with the rise of digital technologies and more flexible content-delivery methods. By the late 20th century, satellite feeds, internet streaming, and multicast digital channels rendered analog subcarriers quaint and unnecessary.

Still, SCA subcarrier signals remain a fascinating piece of broadcasting history. A few still linger today, but it’s now a more obscure medium than ever, lost as mainstream technology has moved on. It’s a reminder that even in the old days of broadcast radio, clever engineers found ways to pack more data into the same old bandwidth—long before we started streaming everything in sight.

Featured image by [windytan].  (Also, check out her work on RDS demodulation.)

If you were in Tunisia in October, you might have caught some of the Morse Code championships this year. If you didn’t make it, you could catch the BBC’s documentary about the event, and you might be surprised at some of the details. For example, you probably think sending and receiving Morse code is only for the elderly. Yet the defending champion is 13 years old.

Teams from around the world participated. There was stiff competition from Russia, Japan, Kuwait, and Romania. However, for some reason, Belarus wins “almost every time.” Many Eastern European countries have children’s clubs that teach code. Russia and Belarus have government-sponsored teams.

Morse code is very useful to amateur radio operators because it allows them to travel vast distances using little power and simple equipment.  Morse code can also assist people who otherwise might have problems communicating, and some assistive devices use code, including a Morse code-to-speech ring the podcast covers.

The speed records are amazing and a young man named [Ianis] set a new record of 1,126 marks per minute. Code speed is a little tricky since things like the gap size and what you consider a word or character matter, but that’s still a staggering speed, which we estimate to be about 255 words per minute. While we can copy code just fine, at these speeds, it sounds more like modem noises.

Learning Morse code isn’t as hard as it sounds. Your computer can help you learn, but in the old days, you had to rely on paper tape.

For the amateur radio operator with that on-the-go lifestyle, nothing is more important than having your gear as light and packable as possible. If you’re lugging even a modest setup out into the woods, every ounce counts, which is why we love projects like this packable dipole antenna feedpoint.

At its simplest, a dipole antenna is just two pieces of wire cut to a specific, frequency-dependent length connected to a feedline. In practical terms, though, complications arise, such as keeping common-mode currents off the feedline and providing sturdy mechanical support for the antenna to suspend it safely. [Ham Radio Dude]’s design handles both those requirements while staying as small and packable as possible. The design starts with a bifilar 1:1 current balun, which is wound on an FT82-43 ferrite toroid with 22 AWG magnet wire. One side of the balun is connected to a BNC connector while the other is connected to a pair of Wago splice connectors that are glued together. A loop of paracord for mechanical strain relief is added, and the whole thing gets covered in heat-shrink tubing. The antenna is deployed by attaching a feedline to the BNC, clipping quarter-wave wires into the Wago terminals, and hoisting the whole thing aloft. Full build details are in the video below.

People will no doubt be quick to point out that these Wago terminals are rated for a minimum of 18 AWG wire, making them inappropriate for use with fine magnet wire. True enough, but [Dude] was able to get continuity through the Wagos, so the minimum gauge is probably more of an electrical code thing. Still, you’ll want to be careful that the connections stay solid, and it might pay to look at alternatives to the Wago brand, too.