SDRs have been a game changer for radio hobbyists, but for ham radio applications, they often need a little help. That’s especially true of SDR dongles, which don’t have a lot of selectivity in the HF bands. But they’re so darn cheap and fun to play with, what’s a ham to do?

[VK3YE] has an answer, in the form of this homebrew software-defined radio (SDR) helper. It’s got a few features that make using a dongle like the RTL-SDR on the HF bands a little easier and a bit more pleasant. Construction is dead simple and based on what was in the junk bin and includes a potentiometer for attenuating stronger signals, a high-pass filter to tamp down stronger medium-wave broadcast stations, and a series-tuned LC circuit for each of the HF bands to provide some needed selectivity. Everything is wired together ugly-style in a metal enclosure, with a little jiggering needed to isolate the variable capacitor from ground.

The last two-thirds of the video below shows the helper in use on everything from the 11-meter (CB) band down to the AM bands. This would be a great addition to any ham’s SDR toolkit.

We’re not very far into the AI revolution at this point, but we’re far enough to know not to trust AI implicitly. If you accept what ChatGPT or any of the other AI chatbots have to say at face value, you might just embarrass yourself. Or worse, you might make a mistake designing your next antenna.

We’ll explain. [Gregg Messenger (VE6WO)] asked a seemingly simple question about antenna theory: Does an impedance mismatch between the antenna and a coaxial feedline result in common-mode current on the coax shield? It’s an important practical matter, as any ham who has had the painful experience of “RF in the shack” can tell you. They also will likely tell you that common-mode current on the shield is caused by an unbalanced antenna system, not an impedance mismatch. But when [Gregg] asked Google Gemini and ChatGPT that question, the answer came back that impedance mismatch can cause current flow on the shield. So who’s right?

In the first video below, [Gregg] built a simulated ham shack using a 100-MHz signal generator and a length of coaxial feedline. Using a toroidal ferrite core with a couple of turns of magnet wire and a capacitor as a current probe for his oscilloscope, he was unable to find a trace of the signal on the shield even if the feedline was unterminated, which produces the impedance mismatch that the chatbots thought would spell doom. To bring the point home, [Gregg] created another test setup in the second video, this time using a pair of telescoping whip antennas to stand in for a dipole antenna. With the coax connected directly to the dipole, which creates an unbalanced system, he measured a current on the feedline, which got worse when he further unbalanced the system by removing one of the legs. Adding a balun between the feedline and the antenna, which shifts the phase on each leg of the antenna 180° apart, cured the problem.

We found these demonstrations quite useful. It’s always good to see someone taking a chatbot to task over myths and common misperceptions. We look into baluns now and again. Or even ununs.

Do you remember the fourth-place winner in the 2022 Hackaday Prize? If it’s slipped your mind, that’s okay—it was Boondock Echo. It was a radio project that aimed to make it easy to record and playback conversations from two-way radio communications. The project was entered via Hackaday.io, the judges dug it, and it was one of the top projects of that year’s competition.

The project was the brainchild of Mark Hughes and Kaushlesh Chandel. At the 2023 Hackaday Supercon, Mark and Kaushlesh (KC) came back to tell us all about the project, and how far it had come one year after its success in the 2022 Hackaday Prize.

Breaker, Breaker

The talk begins with a simple video explainer of the Boondock Echo project. Basically, it points out the simple problem with two-way radio communications. If you’re not sitting in front of the receiver at the right time, you’re going to miss the message someone’s trying to send you. Unlike cellular communications, Skype calls, or email, there’s no log of missed calls or messages waiting for you. If you weren’t listening, you’re out of luck.

Mark was inspired to create a device to solve these problems by his father’s experience as an emergency responder with FEMA. Often, his father would tell stories about problems with radios and missed transmissions, and Mark had always wondered if something could be done.

Boondock Echo is the device that hopes to change all that. It’s a device designed for recording and playback of two-way radio communications. The hardware is based around the ESP32, which is able to capture analog audio from a radio, digitize it, and submit it to the Boondock Echo online service. This also enables more advanced features—the system can transcribe audio to text, and even do keyword monitoring on the results and email you any important relevant messages.

Rather amazingly, Hackaday actually helped spawn this project. Mark had an idea of what Boondock Echo should do, but he didn’t feel like he had the full set of technical skills to implement it. Then, Mark met KC via a Hackaday Hackchat, and the two started a partnership to develop the project further. Eventually, they won fourth place in the 2022 Hackaday Prize, which netted them a tasty $10,000 which they could use to develop the project further. They then brought in Mark’s friend Jesse on the hardware side, and things really got rolling.

The hope was to start producing and delivering Boondock Echo devices. Of course, nobody is immune to production hell, and it was no different for this team. KC dives into the story of how the device relied on the ESP32-A1S module. When they went to make more, this turned out to be problematic. They found some of the purchased modules worked and some didn’t. Stripping the RF shields off the pre-baked modules, they found that while they all included audio codec chips marked “8388,” some modules had a different layout and functioned differently. And these were parts with FCC IDs, identical part numbers, and everything! This turned into a huge mess that derailed the project for some time. The project had to be retooled to work with the ESP32-based AI Thinker Audio Kit, to which they added a custom “sidekick” board to handle interfacing with the desired radio hardware.

Mark notes that there were some organizational lessons learned through this difficult journey. He talks about the value of planning and budgets when it comes to any attempt to escape the “Valley of Death” as a nascent startup. Mark also explains how Boondock Echo came to seek investors to grow further when he realized they didn’t have the resources to make it on their own.

“You don’t go out asking for $10,000 from family and friends, you go out and you ask for a heck of a lot more than that from professional investors,” explains Mark. “It’s a lot easier to come up with $100,000 than $10,000, because the venture capitalists don’t play in the $10,000 price range.” Of course, he notes that this comes with a tradeoff—investors want a stake in the company in exchange for cold, hard cash. Moving to this mode of operation involved creating a company and then dividing up shares for all the relevant stakeholders—a unique challenge of its own. Mark and KC explain how they handled the growing pains and grew their team from there.

The rest of the talk covers the product itself, and we get a demo of what it can do. KC and Mark show us how the Boondock Echo units capture audio, record it, and submit it to the cloud. From there, we get to see how things like AI transcription, keyword triggers, and notifications work, and there’s even a fun live demo. Beyond that, Mark explains how you can order the hardware via CrowdSupply, and sign up with the Boondock Echo cloud service.

It’s not just neat to see a cool project, it’s neat to see something like this grow from an idea into a fully-fledged business. Even better, it grew out of the Hackaday community itself, and has flourished from there. It’s a wonderful testament to what hackers can achieve with a good idea and the will to pursue it.

Ideally, if you are going to transmit, you want a properly-tuned resonant antenna. But, sometimes, it isn’t practical. [Ham Radio Rookie] knew about random wire antennas but didn’t want a wire antenna. So, he took carbon fiber extension poles and Faraday tape and made a “random stick” antenna. You can check it out in the video below.

We aren’t sure what normal people are doing with 7-meter-long telescoping poles, but — as you might expect — the carbon fiber is not particularly conductive. That’s where the tape comes in. Each section gets some tape, and when you stretch it out, the tape lines up.

We aren’t sure how these poles are constructed, but the video claims that the adjacent sections couple capacitively. We aren’t sure about that as the carbon fiber won’t be very conductive, but it probably isn’t a very good insulator, either. Then again, the poles may have a paint or other coating along the surface. So without seeing it, it is hard to say what’s coupling the elements.

He admits this is experimental and there is more work to do. However, it seems cheap and easy to setup. The hardest part is tapping an M10 hole in the end cap to allow things to mount.

We suppose you could make your own tubes, but it hardly seems worth the trouble. If you cut or drill this stuff, you might want to take precautions.

The regenerative radio is long-ago superseded in commercial receivers, but it remains a common project for electronics or radio enthusiasts seeking to make a simple receiver. It’s most often seen for AM band receivers or perhaps shortwave ham band ones, but it’s a circuit which also works at much higher frequencies. [Perian Marcel] has done just this, with a regenerative receiver for the FM broadcast band.

The principle of a regenerative receiver is that it takes a tuned radio frequency receiver with a wide bandwidth and poor performance, and applies feedback to the point at which the circuit is almost but not quite oscillating. This has the effect of hugely increasing the “Q”, or quality factor of the receiver, giving it much more sensitivity and a narrow bandwidth. They’re tricky to tune but they can give reasonable performance, and they will happily slope-demodulate an FM transmission.

This one uses two tubes from consumer grade TV receivers, the “P” at the start of the part number being the giveaway for a 300mA series heater chain. The RF triode-pentode isn’t a radio part at all, instead it’s a mundane TV field oscillator part pushed into service at higher frequencies, while the other triode-pentode serves as an audio amplifier. The original circuit from which this one is adapted is available online, All in all it’s a neat project, and a reminder that exotic parts aren’t always necessary at higher frequencies. The video is below the break.

If you’re planning on working satellites or doing any sort of RF work where the signal lives down in the dirt, you’re going to need a low-noise amplifier. That’s typically not a problem, as the market is littered with dozens of cheap options that can be delivered in a day or two — you just pay your money and get to work. But is there a case to be made for rolling your own LNA?

[Salil, aka Nuclearrambo] thinks so, and he did a nice job showing us how it’s done. The first step, as always, is to define your specs, which for [Salil] were pretty modest: a low noise figure, moderate gain, and good linearity. He also wanted a bandpass filter for the 2-meter amateur radio band and for weather satellite downlinks, and a bias-tee to power the LNA over the coax feedline. The blog post has a detailed discussion of the electrical design, plus some good tips on PCB design for RF applications. We also found the discussion on bias-tee design helpful, especially for anyone who has ever struggled with the idea that RF and DC can get along together on a single piece of coax. Part 2 concentrates on testing the LNA, mostly using hobbyist-grade test gear like the NanoVNA and tiny SA spectrum analyzer. [Salil]’s tests showed the LNA lived up to the design specs and more, making it more than ready to put to work with an RTL-SDR.

Was this more work than buying an LNA? Absolutely, and probably with the same results. But then again, what’s to learn by just getting a pre-built module in the mail?

We love seeing the incredible work many RF enthusiasts manage to pull off — they make it look so easy! Though RF can be tricky, it’s not quite the voodoo black art that it’s often made out to be. Many radio protocols are relatively simple and with tools like gnuradio and PocketSDR you can quickly put together a small system to receive and decode just about anything.

[Jean-Michel] wanted to learn more about GNSS and USB communication. Whenever you start a project like this, it’s a good idea to take a look around at existing projects for designs or code you can reuse, and in this case, the main RF front-end board is taken from the PocketSDR project. This is then paired with a Cypress FX2 development board, and he re-wrote almost all of the PocketSDR code so that it would compile using sdcc instead of the proprietary Keil compiler. Testing involved slowly porting the code while learning about using Python 3 to receive data over USB, and using other equipment to simulate antenna diversity (using multiple antennas to increase the signal-to-noise ratio):

The main board uses two MAX2771 GNSS front-ends, which filter and convert the received signals to either a digital output or optionally as I and Q outputs for conversion with discrete ADCs. This data is then read by the 8051 core on the FX2, and the data is sent over USB to maintain a fast and reliable stream. On the PC side, this can be decoded using the original PocketSDR software, or one can build a decoder using gnuradio.

The result is a working GNSS decoder. If you would like to see more detail about the project, [Jean-Michel] put together a YouTube video talking about his work in cloning and porting the code, which you can see below:

As far as hobbies go, ham radio tends to be on the more expensive side. A dual-band mobile radio can easily run $600, and a high-end HF base station with the capability of more than 100 watts will easily be in the thousands of dollars. But, like most things, there’s an aspect to the hobby that can be incredibly inexpensive and accessible to newcomers. Crystal radios, for example, can be built largely from stuff most of us would have in our parts drawers, CW QRP radios don’t need much more than that, and sometimes even the highest-performing antennas are little more than two lengths of wire.

For this specific antenna, [W3CT] is putting together an inverted-V which is a type of dipole antenna. Rather than each of the dipole’s legs being straight, the center is suspended at some point relatively high above ground with the two ends closer to the earth. Dipoles, including inverted-Vs, are resonant antennas, meaning that they don’t need any tuning between them and the radio so the only thing needed to match the antenna to the feed line is a coax-to-banana adapter. From there it’s as simple as attaching the two measured lengths of wire for the target band and hoisting the center of the antenna up somehow. In [W3CT]’s case he’s using a mast which would break the $8 budget, but a tree or building will do just as well.

The video on the construction of this antenna goes into great detail, so if you haven’t built a dipole yet or you’re just getting started on your ham radio journey, it’s a great place to get started. From there we’d recommend checking out an off-center-fed dipole which lets a dipole operate efficiently on multiple bands instead of just one, and for more general ham radio advice without breaking the bank we’d always recommend the $50 Ham series.

It probably comes as little surprise that our planet is practically buzzing with radio waves. Most of it is of our own making, with cell phones, microwaves, WiFi, and broadcasts up and down the spectrum whizzing around all the time. But our transmissions aren’t the only RF show in town, as the Earth itself is more than capable of generating radio signals of its own, signals which you can explore with a simple sferics receiver like this one.

If you’ve never heard of sferics and other natural radio phenomena, we have a primer to get you started. Briefly, sferics, short for “atmospherics,” are RF signals in the VLF range generated by the millions of lightning discharges that strike the Earth daily. Tuning into them is a pretty simple proposition, as [DX Explorer]’s receiver demonstrates. His circuit, which is based on a design by [K8TND], is just a single JFET surrounded by a few caps and resistors, plus a simple trap to filter out the strong AM broadcast signals in his area. The output of the RF amplifier goes directly into an audio amp, which could be anything you have handy — but you risk breaking [Elliot]’s heart if you don’t use his beloved LM386.

This is definitely a “nothing fancy” build, with the RF section built ugly style on a scrap of PCB and a simple telescopic whip used for an antenna. Tuning into the Earth’s radio signals does take some care, though. Getting far away from power lines is important, to limit AC interference. [DX Explorer] also found how he held the receiver was important; unless he was touching the ground plane of the receiver, the receiver started self-oscillating. But the pips, crackles, and pings came in loud and clear on his rig; check out the video below for the VLF action.

We’ve always been fascinated by things that perform complex electronic functions merely by virtue of their shapes. Waveguides come to mind, but so do active elements like filters made from nothing but PCB traces, which is the subject of this interesting video by [FesZ].

Of course, it’s not quite that simple. A PCB is more than just copper, of course, and the properties of the substrate have to be taken into account when designing these elements. To demonstrate this, [FesZ] used an online tool to design a bandpass filter for ADSB signals. He designed two filters, one using standard FR4 substrate and the other using the more exotic PTFE.

He put both filters to the test, first on the spectrum analyzer. The center frequencies were a bit off, but he took care of that by shortening the traces slightly with a knife. The thing that really stood out to us was the difference in insertion loss between the two substrates, with the PTFE being much less lossy. The PTFE filter was also much more selective, with a tighter pass band than the FR4. PTFE was also much more thermostable than FR4, which had a larger shift in center frequency and increased loss after heating than the PTFE. [FesZ] also did a more real-world test and found that both filters did a good job damping down RF signals across the spectrum, even the tricky and pervasive FM broadcast signals that bedevil ADSB experimenters.

Although we would have liked a better explanation of design details such as via stitching and trace finish selection, we always enjoy these lessons by [FesZ]. He has a knack for explaining abstract concepts through concrete examples; anyone who can make coax stubs and cavity filters understandable has our seal of approval.

The Quansheng UV-K5 is a popular handheld radio. It’s useful out of the box, but also cherished for its modification potential. [OM0ET] purchased one of these capable VHF/UHF radios, but got to hacking—as he wanted to use it as a desktop radio instead!

This might just sound like a simple reshell, but there was actually a bit of extra work involved. Most notably, the Quansheng is designed to be tuned solely by using the keypad. For desktop use, though, that’s actually kind of a pain. Thus, to make life easier, [OM0ET] decided to whip up a little encoder control to handle tuning and other control tasks using an ESP32. This was achieved with help from one [OM0WT] and files for that are on Github. Other tasks involved finding a way to make the keypad work in a new housing, and how to adapt things like the audio and data module and the speaker to their new homes.

Despite the original handheld being much smaller than the case used here, you’d be surprised how tight everything fits in the case. Still, the finished result looks great. We’ve seen some other adaptable and upgradable ham radio gear before, too. Sometimes custom is the way to go! Video after the break.

It’s a staple of spy thriller movies, that the protagonist has some kind of electronic scanner with which he theatrically searches his hotel room to reveal the bad guys’ attempt to bug him. The bug of course always had a flashing LED to make it really obvious to viewers, and the scanner was made by the props department to look all cool and futuristic.

It’s not so far-fetched though, while bugs and hidden cameras in for example an Airbnb may not have flashing LEDs, they still emit RF and can be detected with a signal strength meter. That’s the premise behind [RamboRogers]’ RF hunter, the spy movie electronic scanner made real.

At the rear of the device is an ESP32, but the front end is an AD8317 RF detector chip. This is an interesting and useful component, in that it contains a logarithmic amplifier such that it produces a voltage proportional to the RF input in decibels. You’ll find it at the heart of an RF power meter, but it’s also perfect for a precision field strength meter like this one. That movie spy would have a much higher chance of finding the bug with one of these.

For the real spies of course, the instruments are much more sophisticated.

Anyone who works with radio transmitters will know all about matching and impedance, and also about the importance of selecting the best co-axial cable connecting transistor and antenna. But here’s [Steve, KD2WTU] with a different take, he’s suggesting that sometimes a not-so-good co-ax choice can make the grade. He’s passing up expensive 50 ohm cable in favour of the cheap and ubiquitous 75 ohm RG6 cable used in domestic TV and satellite receiver installations.

Fighting that received wisdom, he outlines the case for RG6. It’s cheap and it has a surprisingly low loss figure compared to some more conventional choices, something that shouldn’t be a surprise once we consider that it’s designed to carry GHz-plus signals. Where it loses is in having a lower maximum power rating. Power shouldn’t be a problem to a shoestring ham for whom 100W is QRO. Another issue is that 75 ohm coax necessitates a tuner for 50 ohm transmitters. It also has the effect of changing the resonance of some antennas, meaning a few mods may be in order.

So we’re convinced, and with the relatively QRP shack here we can’t see RG6 being a problem. Maybe it’s something to try in out next antenna experiment. Meanwhile if you’re interested in some of the background on co-ax impedance choices, we’ve been there before.