Software-defined radios represent “the next level of shortwave radio listening,” says convert James Careless – writing a piece espousing the technology’s benefits for Future Publishing’s Radio World magazine.
“Where have these things been all my life,” James rhetoricises after being introduced to the world of software-defined radio systems. “There is a new breed of RF receivers known as software-defined radios, and they are revolutionising the way in which people listen to shortwave (SW) radio, or indeed any form of radio broadcast.”
Explaining that SDR hardware allows the listener to “literally see what is happening across the band in real time,” James claims the devices are “an absolute must for anyone who likes to tune around the bands.” He should know: James has been listening to shortwave radio for more than 40 years, having started out on a 1950s Nordmende console. “Being able to see the band being tuned to is an absolute gift. At a glance, you can see which bands have lots of possible targets and which do not. Tuning can be done by using the mouse and scroll wheel.”
This turned out to deliver what James refers to as “unexpected stations” – signals from Botswana, Tinian Island, and Ascension Island, all received in a second-floor radio room in Ottawa. “Had I understood just how useful and cool these devices are,” he concludes, “I would have got them years ago.”
The full article is available in the August 1 issue of Radio World magazine, P16-19.
Jon Dawson has also been experimenting with low-cost receive-only software-defined radios, but with a rather more homebrew approach – turning a Raspberry Pi Pico microcontroller board into a working radio capable of standalone operation.
“A couple of years ago, I built a basic yet capable radio receiver using a [Raspberry] Pi Pico,” Jon explains, “and while I originally designed a custom PCB for it, this time I’m building an even simpler and cheaper version that can be built on a breadboard using (mostly) through-hole components. I wanted to build a very minimal (but useful) design that I could use as a platform for experiments, tweaks, and upgrades.
“The design uses a ‘Tayloe’ Quadrature Sampling Detector (QSD) popularised by Dan Tayloe […] and used in many HF [High-Frequency] SDR radio designs. This simple, design allows a high-quality mixer to be implemented using an inexpensive analogue switch. A quadrature oscillator is generated using the PIO [Programmable Input/Output] feature of the RP2040. This eliminates the need to use an external programmable oscillator.
“The receiver covers frequencies up to 30MHz,” Jon concludes, “including commercial broadcasts on Longwave, Medium Wave, Shortwave, and the HF amateur radio bands. What’s great about this design is that it’s completely standalone – it doesn’t need a PC or sound card and can run for hours on just three AAA batteries.”
The design is shown in detail, with schematics, on Jon’s website; source code and a pre-compiled firmware are available on GitHub under the permissive MIT licence.
Researchers at China’s XiDian University and the Xi’an Institute of Space Radio Technology, working with the APT Satellite Company, have come up with a new approach to designing multi-beam antennas with artificial intelligence assisted optimisation – and say it could be key to delivering a sixth-generation (6G) satellite network.
“The active multi-beam antenna can be widely used in the 6G integrated satellite network project, the national satellite Internet project, and other major satellite projects,” the team explains. “It determines the key performance indicators of the satellite such as the service coverage area and the communication capacity of all the beams in the forward link and the return link. The active multi-beam antenna is the core technology of satellite payload and has been developed rapidly in recent years.
“Based on the antenna performance requirements such as the number of giant-scale beams, super-large coverage area, high gain, and high carrier-to-interference ratio (C/I), this paper proposes a new active multi-beam antenna design method, which integrates the multi-objective coordination and multi-feed amplitude and phase weighted optimisation algorithms. A balanced optimal solution that meets the performance requirements can be obtained by constraining each other with different objective functions. In the optimisation process, the surrogate model of convolutional autoencoder based on artificial intelligence technology is proposed for multi-objective optimisation solution, which efficiently completes the search of optimal beam excitation coefficients.
“This paper takes the demand for very-high-throughput communication satellites serving the Asia-Pacific region as an example,” the team explains, “and applies the design method to the multi-beam antenna design of the satellite. The simulation verification of the antenna is completed, achieving good performance of 976 beams. All results meet the performance requirements, supporting the implementation of 1Tbps communication capacity for the entire satellite, and verifying the correctness of the design method.”
The full paper is available under open-access terms in the journal Space: Science & Technology.
Also turning their attention to space is pseudonymous YouTuber “331RL328”, who has been peering at the Perseid meteor shower using a software-defined radio.
Visible in the sky, clouds permitting, from mid July to mid August each year, the Perseids – named for the sons of Perseus – are the result of the Earth crossing the path of debris from the Swift-Tuttle comet. Typically, the meteors can be seen as shooting stars and fireballs by the naked eye as they burn in the upper atmosphere – but 331RL328 has been visualising their paths using radio signals, instead, which is at least less affected by cloud cover.
In the near-seven-minute video, 331RL328 delivers a view of the Perseids as seen using the 143.05MHz Graves space-surveillance radar as a signal source – recording echoes as they bounce from the meteors gliding through the sky above. Visually, they show up as bright “sparks” in the waterfall graph – though the audio is, perhaps, uncomfortable listening at higher volumes.
The full video is available on 331RL328’s YouTube channel.
Bob “KD4BMG” Hughes, also known as the HOA Ham, is continuing to expand his antenna collection with designs that won’t draw the attention of his local home owners’ association – this time installing an antenna in his guttering to hide it from view.
“Gutter antennas? Antennas hiding in plain sight? Stealthing the HOA? I’m all about that,” Bob explains. “I’m not afraid to try something new and different. [I have] an aluminium downspout [that’s] just begging to be tested. I didn’t think of this when I installed the [Chameleon Antenna] URT-1 [Remote Tuner], but it’s in a perfect location to just take a two-foot piece of wire, take it on over to the downspout, hook it up, and see if I can make contacts.”
Initial testing proved positive, despite very carefully managed expectations. “My downspout has been painted multiple times over, so I don’t know how many coats of paint are on these products – [and] they’re all aluminium. This is aluminium downspout, aluminium gutter, aluminium fascia, aluminium soffit, so my concern was ‘is my signal going to get out with all the layers of paint, and I’ve got aluminium on top of aluminium on top of aluminium, and that fascia wraps around the end of my house – where does my antenna end?”
The full project, including contact results, is available on Bob’s YouTube channel.
Self-described “lifelong maker, tinker, and hacker” Robert Hart is also working with radios in a built-up area, but has opted to trade visibility for portability in the creation of a low-noise Moebius loop antenna for high frequency (HF) operation.
“I was running one of my IoT [Internet of Things] workshops at the library on SDR receivers; however, receiving signals below 50MHz in an urban area is very difficult, particularly in a library,” Robert writes. “Conventional HF antennas are often many metres in size. VHF and UHF were relatively easy, but HF is almost impossible due to limited space and radio noise. One solution to this problem was using a Moebius magnetic loop antenna.
“[These are] also called a small loop, as it has a diameter smaller than half the operating wavelength (typically no more than 1/3 to 1/4 wavelength). Loop antennas are used mainly as receiving antennas but are sometimes used for transmission. The radiation pattern of a loop antenna is maximum at directions within the plane of the loop, so perpendicular to the maxima of large loops.
“I had an unused roll of N-terminated Andrew LDF4-50A HELIAX 1/2″ Corrugated Coaxial Cable, which I’ve used for microwave experiment,” Robert says. “It is quite ridged, and I thought this would make an excellent stiff loop. It is also very low-loss. So, I cut it into two lengths to make a loop approximately 1.2 metres in diameter, removing the ends for termination. I found a plastic enclosure, fitted cable glands and soldered the two ends for the Moebius configuration. Then, I set about winding a 1:1 Balun from instructions I found on Peter Miles, VK6YSF website.”
The full build log is available on Hackaday.io.
Pseudonymous Redditor “Trick_Camp_6283,” hereafter simply “Camp,” is also working with homebrew antennas, upcycled from discarded satellite dishes and plastic drinks bottles – pointing them at the sky in order to pull in data from geostationary satellites.
“I have made this antenna with a very common dish available in India which comes with the brand DishTv,” Camp explains. “It’s an 80cm dish, and by calculations the focal point should be between 37 to 41cm, but for me it works best on 35.8cm. I’m using a simple dipole for this, and I am using 1mm thick copper sheet. Each dipole is 4.2cm long and 1.5cm wide.
“Copper coax work best in this case which is RG58, [I] couldn’t use LMR400 cause its difficult to work with. In the bottle I have secured SAWbird + GOES filter. I was going to buy [a] Nooelec GOES boom antenna, but it was way too costly for its purpose. I have also made an helical antenna add-on for this dish, but due to smaller size of dish it isn’t working properly, [I] hope somehow I make it work.”
Despite the upcycled parts and field-expedient bottle housing, the antenna’s performance seems impressive with Camp sharing crisp and clear images captured from weather satellites in the project’s Reddit thread.
Fellow pseudonymous Redditor “Chris56855865,” hereafter simply “Chris,” has also been working on antennas for satellite reception – though the “Craptenna” is built from considerably more humble components.
“The Craptenna [is] literally made from some garbage fence board, a pair of dry twigs, cable ties, a bit of choc bloc, and a thin solid core copper wire with old 75 ohm TV coax,” Chris writes. “It’s going to be replaced by a QFH once my friend gets some ABS plastic for his 3D printer, I made this more of a stopgap solution so that I don’t have to go out 5kms to a nearby field to get good data. Also, it’s to show that one can make an antenna out of rubbish, plus it has been fun.”
While the Craptenna was usable, it was soon replaced. “Goodbye Craptenna,” Chris writes in a follow-up post. “Welcome 3D printed, aluminium rod 120° V-Dipole! The Shed™ has a new crown. I didn’t measure anything, I don’t have the means to do so. The cable is 75 ohm RG6 anyways, so probably not anywhere near 50 [ohms] on the whole. I shaped the aluminium rods’ inside end to fit the choc block, and I didn’t use a connector, they are directly connected to the cable.
“[The results are] not that good unfortunately, it has more nulls than the junk antenna had, probably due to positioning. I also have a QFH built that I want to try. Also, the shed has sheet aluminium roofing (it used to be cheap in the ’70s and ’80s where I live), and that is more than likely an issue too.”
The Craptenna and its follow-up have their own respective Reddit posts for more discussion.
Finally, Michael Simpson has been playing with a little piece of radio history, from before the days anything available in shops could be described as “software-defined”: a Philmore VC-1000 crystal radio kit, released in the 1960s.
“I’ve been trying to date this radio to the exact year, but I’m not having much luck. Both the box and the radio are labelled ‘Model VC-1000’, but the radio on the box doesn’t match the radio. On the box there’s an extra antenna connection, and the diode’s up here. Now, in the 1960s Philmore catalogue, this is the radio you got – so we can consider this to be post 1960, since they’ve enacted some cost-cutting measures and removed this [second antenna] connection. So, let’s give this a tentative date of 1964.
“It’s picking up one station,” Michael found after firing the radio up, “[but] I don’t seem to be able to tune anything: when I turn the knob for the variable capacitor, nothing’s happening. We’ve got a bad solder joint, so I’ll reheat that solder joint and see if the performance improves any.”
Sadly, that didn’t solve the problem, with the tuner still working only intermittently. Replacing the variable capacitor with a new-old stock version, though, got everything up and running as it should – while the bracket holding it to the base of the radio was cleaned of 60 years of oxidisation.
The full process – along with a few comedy skits, mild explosions, and a story about crystal earpieces – is detailed in Michael’s YouTube video.