Setting Up the USRP X410
In the dim glow of my late‑night workstation, the USRP X410 sat on the desk, its cooling fans humming like a quiet wind turbine. I attached the small daughterboard that would convert the 3.5 mm connector to the standard U.FL sockets, then mounted the X410 into a compact enclosure to keep dust at bay. The first step was to flash the latest UHD firmware, which the vendor’s website had described as stable and fully compatible with my Linux distribution. After rebooting, I trimmed the firmware configuration with the driver’s uhd_usrp_probe utility and verified that the device responded at 1.5 GHz, the archetypal voice band of the X410.
Turning on the Radio
I loaded GNU Radio and dropped in a flow‑graph that would tune the X410 to 7.0 MHz, the classic amateur band where WSPR traffic often glides unnoticed between stations. Using the blockchain slider, I set the sample rate to 250 kS/s, a sweet spot that comfortably captured the 50‑Hz Hanning window of the WSPR transmitter without overloading the memory buffer. The receiver’s front‑end gain, a wizardly parameter, was pinned to 0 dB to keep the passband flat while letting the digital gate open for the weak replies that define WSPR.
Listening for the Silent Messages
At 07:57 UTC on the 14th, a faint burst shimmered across my waterfall display. The symbol appeared on 14.000 MHz, precisely where the X410’s frequency selector had been set. I half‑expected it to be nothing more than a phantom echo, yet the demodulation block lighted up with a Roger–Roger ACK from a far‑off station. I noted the marker’s time stamp and repeated the capture, confirming a real WSPR return on the same frequency. Then I drifted the receiver to 24.9 MHz, where an indistinguishable tone emerged after a storm of static. The story unfolded: WSPR uses the main amateur allocations, specifically 2.5 MHz, 4.9 MHz, 7.0 MHz, 10.1 MHz, 14.0 MHz, 18.1 MHz, 21.0 MHz, 24.9 MHz, 28.0 MHz, and 50.0 MHz. Each band provides an opportunity for the undersea of signals to ripple across the globe.
Digging Deeper and The Power of Data
Because the X410 can stream data at multi‑Gigabit links, I made a simple script that captured continuous bursts over a 10‑minute window on all WSPR frequencies. Inside the log file, the timestamps aligned with the official WSPR reporting schedule. I replayed the raw data through a custom Python decoder that used Gr‑WSPR libraries to pull out the transmission callsigns and compute the round‑trip SNR. The reader now can see exactly how little power—a 28 dB WSPR signal—can be extracted from a stage that routinely exceeds 100 dB of background noise.
From Hobbyist to Radar Archivist
When the capture pipeline was sorted, I turned the X410 into a small archive station. Every 5 years the community runs a specific WSPR “testing cycle” on the 2.5 MHz band to read the channel state. The X410’s enormous bandwidth lets me record the entire 2–54 MHz range, and the data can later be repurposed for WI‑Ks and Propagation Map projects. The story of my night‑time listening sessions is now a part of a larger science‑driven narrative—the USRP X410 forever listening to the faint whispers of radio explorers across the planet.
When Voice Came From the Quiet Street
The first dawn of the project was quiet, the only sound a distant hum from the city. I had recently unpacked the USRP X410, a powerful rig that feels more like a satellite dish than a handheld box. Its versatility—ranging from 1 GHz to 6 GHz—seemed to promise a world of possibilities. Yet my curiosity was set far lower, deep in the 15 MHz band where the elusive WSPR-15 signals hum.
Finding the Right Frequency
WSPR-15 takes its place at 15 073 kHz (15.073 MHz), a sweet spot that draws reverse‑directional radiators across the globe. This narrow channel, only 600 Hz wide, works wonders for weak‑signal experiments and is a favourite among those who love to test the limits of amateur radio links. The challenge was clear: hook the X410 to a frequency translator that could strip the 15 MHz tone down into the X410’s 1‑6 GHz span.
Building the Bridge
With a simple 10–15 MHz tuner and a low‑noise amplifier, I built a pass‑band filter that strips everything but our band of interest. The mixer then down‑converted 15 MHz to a 0–200 MHz range, perfectly suited for the X410’s daughterboard. When the first sweep of the tuner synced with \–15 073 kHz, the screen lit up, and the WSPR-15 constellation unfolded like a germinating plant.
Listening to the Global Thread
It felt like watching a city’s heartbeat on a grid of colorful dots. With the Gnu Radio flow‑graph I set up—an FFT window, a WSPR decoder, and a live plotting tool—each dot represented a message pressed into the ether. A 90‑amp lamp in the back row and a low‑power node in over a thousand miles away both shared the same invisible link.
Decoding the Silent Handshake
WSPR messages are packed with a unique identifier, power level, and a timestamp hidden in a 72‑bit packet. Using the open‑source WsprDecode script, the X410 could not only detect these packets but also help map the signal’s path from transmitter to receiver. By pausing the GAIN slider, I could compress the noisy fringe into a clean burst of letters: a perfect demonstration of how a high‑speaking electron’s whisper could be heard over Earth.
Sharing the Story
After months of tuning, I finally built a live dashboard that displayed WSPR-15 traffic across the global network. Each visible cluster of dots was a story—of a dream, a classroom, or a backyard experiment. There was a lesson in humility and a lesson in possibility: even a 15 MHz whisper could echo for thousands of kilometers.
What Lies Ahead
The journey is ongoing. There is a new, narrow band just opening on
Night on the Shoreline
On a cool Saturday evening, I set up my USRP X410 SDR on the railing of the old pier, the cold breeze brushing the glossy metal of the antenna. The quiet of the water below interrupted only by the distant hum of traffic was the perfect backdrop for a hunt on the airwaves. The X410, with its four dual‑band (HF and VHF/UHF) daughterboards, buzzed as it captured the faint whispers of distant explorers in the amateur radio sky.
Gateway to the World of FT‑8
My goal was simple yet bold: to monitor the FT‑8 signals on the amateur radio bands with the precision that only a modern SDR can provide. FT‑8, the 15‑second slow‑moving digital mode, operates over a 6.25 kHz channel centred on each 6.25 kHz step. By tuning the X410 to a narrow 12 kHz slice around a target frequency, the device isolates the tiny 6.25 kHz signal within, allowing the software to decode the complex 12‑beam time‑code used by >2,000 operators worldwide.
Frequencies That Speak the Quiet Language of FT‑8
After scanning the spectrum, I set the X410 to the following key frequencies, each a gateway for FT‑8 traffic across the globe:
70 cm (437 MHz band): 437.175 MHz – the 1‑meter band’s classic hot spot for near‑field FT‑8 contacts.
23 m (13 MHz band): 13.020 MHz – the only band that offers a clean 6.25 kHz bandwidth for FT‑8, ideal for sunrise‑sunset experimentation.
20 m (14 MHz band): 14.018 MHz – the high‑frequency companion to 70 cm, where long‑range, 15‑second hops are frequent.
15 m (21 MHz band): 21.015 MHz – the world where skywave FT‑8 operates, reaching continents away in clear conjunction windows.
These frequencies sit neatly in the SDR’s digital filter, each routed through the X410’s high‑performance ADCs to the host computer for live plotting.
Listening Through the Lens of Software
I launched SDR# on the host workstation and applied a 12 kHz mix filter centered on 14.018 MHz. The waterfall revealed the distinctive “XXX‑YYY‑ZZZ” tone pattern, a breath‑taking tapestry of 50‑carrier pulses. The FT‑8 DSP engine decoded the message, unveiling the call sign, state, and message content in seconds. The data spooled into a neat XML log, ready to cross‑reference with IARU Region 2 stations.
A Tale of Data and Discovery
Back at the pier, the X410 glimmered like a constellatory halo, silently collecting an entire night’s worth of FT‑8 packets. Each packet, a simple 6‑symbol word, etched a story across the spectrum—a narrative of shifts, times, and tiny signals steering through the air. On my screen, the time‑code danced with immaculate timing, proof that the SDR’s high‑granularity timestamps matched the FT‑8 clock reference to within a fraction of a second.
Reflections Beneath the Stars
When the last signal faded, the X410’s chimes whispered a satisfying conclusion. The night had proven that with the USRP X410 and a single finely tuned frequency, the realm of FT‑8 offers a window into the world’s quiet, patient radio community. And as the tide crept toward the rocks, I felt a deep connection to every operator out there, each using the same simple 6.25 kHz frame to share a quiet word in the night sky.
A Quiet Dawn on the Spectrum
When the sun crests the horizon, the world of radio frequencies is still draped in its own quiet hush. It was in one of those early mornings, with the air thick with anticipation, that I set up my USRP X410 SDR on the porch of my loft. The X410, with its wideband tuning from 50 MHz up to 2 GHz, promises to be a perfect companion for anyone looking to listen to the most elusive whispers that travel half a kilometre across oceans or lie hidden just under the flickering of the amateur bands.
Curious Inquiries into FT‑4
For the love of navigation and a taste of digital mystery, I had long wanted to capture the FT‑4 signals that are the backbone of maritime direction-finding. FT‑4, the four‑tone frequency‑modulated mode defined by the ITU‑R, sits in a narrow 1.5 kHz sub‑band nestled between 163.250 MHz and 164.250 MHz in the most frequent allocation today. These signals, registered in 2024 and still carried by coastal beacons and offshore platforms, are a living testament to how we use precise digital modulation for safety and interoperability.
Trial with the Antenna and the X410
My first step was to coax the SDR into the right frame of mind. I set the centre frequency to 163.750 MHz, the median of the FT‑4 band, and chose a sampling rate of 2 Msps. That rate is more than enough to capture the 1.5 kHz width while giving me enough headroom to filter out the subtle spectral splashes that always creep in from the surrounding amateur activity.
The Tuning of the Curious Mariner
The X410’s internal decimation and digital filter chain proved invaluable, letting me trim the incoming stream down to a clean 4 kHz band that neatly encompassed the FT‑4 signal. In the Ireland tracts this conversion is heard less than a few kilometers north, and there I could directly hear the four identical tones that form the FT‑4 signal’s signature.
Stepping into the Waves
It was a rainy Thursday evening when Alex first decided to bring the USRP X410 out of its chassis and into the quiet corners of the home lab. He had heard whispers about an emerging “OLIVIA” signal, a beacon that promised to make small‑scale amateur radio operators feel like they were part of a global orchestra. The X410, with its seven 1–6 GHz front‑end boards, seemed the perfect instrument for this mission, capable of sweeping everything from the gentle notes of the 10‑meter band to the bassy pulses of the 70‑centimeter band with the same ease.
Preparing the Instrument
Alex attached a whisper‑quiet dual‑band antenna to the X410’s antenna connection 1 and opened SoapySDR# alongside GNU Radio Companion. He set the device type to iio_usrp_x410, chose a central frequency of 145.830 MHz—where the eastern VHF sky flickers with satellite chatter—and applied a 5 MHz bandwidth. The X410’s adjustable gain knob thumbed up to just the right level, catching the faint crescendos of every passing signal.
The OLIVIA Signature
Within a few minutes, the waterfall plot flickered to life. A distinct FM carrier emerged, drifting gently between 145.800 MHz and 145.860 MHz in a rhythmic pulsing pattern. Alex read the hint in the frequency drift: the OLIVIA system uses dual sidebands, a design that allows the signal to survive atmospheric hiss on the crowded 10‑meter line. When he turned the lens of his digital oscilloscope to the lower‑frequency side, a faint radio‑frequency interference drifted between 435.550 MHz and 435.650 MHz, revealing that OLIVIA was not limited to the VHF spectrum. On the lower edge of that band, the X410’s wideband capability captured a hair‑thin, pulsed burst at 437.400 MHz, the satellite’s secondary transponder window.
Fine‑Tuning and Capture
Knowing that the X410’s common IQ sampler could push a maximum of 6 GHz, Alex built a looping script in GNU Radio to sequentially sweep from 140.0 MHz to 141.0 MHz, then to the UHF range from 436.0 MHz to 438.0 MHz. By applying a 30 dB fixed gain and a 15 kHz low‑pass filter to each hop, he managed to isolate the OL
Listening to the Invisible Chorus with the USRP X410
In the quiet hours of dawn, the world outside my window turned dark, and the only light came from screens and antennae swinging gently in the wind. I had recently acquired the USRP X410, a powerful software‑defined radio that promised a passport to the electromagnetic ocean. Its 108 MHz to 2.4 GHz bandwidth opened vast swaths of the amateur radio spectrum to my curiosity.
At first, I set it to sweep the 144–148 MHz band, the familiar airspace of the beloved 2‑meter group. There, the 145.7 MHz beacon of my local club was unmistakable. I could hear its translated chatter, a stream of MT63 encoded voice traffic that flowed with the same rhythm as a distant drum.
Drifting into 70‑Centimeter Frees
Once my ears were attuned to the 2‑meter band, I turned the tuner to the ripple of the 437–450 MHz band, the realm of 70‑centimeter operators. Here the 470.1 MHz channel often whispered a steady stream of MT63 exchanges between hobbyists across the globe. I imagined the signals literally nesting in tiny cavities of the atmosphere, folding each second like origami and emerging in perfect square‑wave harmony.
Grabbing the Terrain with Software
The X410’s integrated FPGA and SDR foundation let me build custom filters for each band instantly. I crafted a narrow band‑pass around 145.2–145.4 MHz for the 2‑meter group and another around 470.1–470.3 MHz for the 70‑centimeter line. By slamming the appropriate constants onto the X410, I could tune in MT63 chatter with a clarity that kept the code from glitching, preserving the waveform’s integrity even when neighboring chatter fused at the edge.
Living Within the Waves
With every faithful sweep, I learned how the same modulation scheme—MT63, a burst of bit‑streams—could be embedded across different amateur radio bands. By carefully setting the USRP X410 to 145.7 MHz or 470.1 MHz, I could see the vibrations ripple through the Vista of the sky. Each burst turned the simple digital pulse into words, laughter, and the old bond of communication that roots us in the unpredictable landscape of the radio.
It All Begins in the Quiet of the Night
In the chill of early evening, when the streetlights flickered like distant stars, I turned on my USRP X410 and let the waves of air speak to me. The box hummed softly, a reminder that this narrow slice of the spectrum could hold mysteries of its own.
The Hardware That Opens the World
For anyone who wishes to hear what is hidden between the twinkles of radio waves, the USRP X410 is a swift bridge. With a wideband front‑end that effortlessly covers 50 MHz to 600 MHz, it spans the prime amateur radio windows I was eager to explore. Its 14‑bit ADC and expandable RF paths let me tune in with precision, making the distant voices on the air feel almost close.
Seeking the Silent Language of PSK‑31
I set the device to the 20‑meter band first, a family of frequencies that hum with communications between hobbyists, emergency teams, and the curious. PSK‑31, a minimalist digital mode, often listens on 14.070 MHz. I turned the receiver’s frequency knob slowly, watching the signal rise in a steady, barely‑there hiss that was almost as delicate as a whisper in the wind.
Expanding the Horizon Across the Bands
My exploration was not limited to the 20‑meter band. On the 40‑meter band the same PSK‑31 chatter resided at 7.040 MHz, a frequency that lies in the familiar low‑frequency chatter of the ham community. Later that night, I slid to 15‑meter, where the language shifted to 21.020 MHz, and then to the 30‑meter band, a second, more rarely used window, where PSK‑31 messages drifted at 10.050 MHz. Each band offered a different texture, as if the same song were sung in various dialects.
Listening as a Story Unfolds
As I listened, the messages began to shape a narrative of its own. Friends on the other side of the world answered my request in slashing bursts of binary, and the faint voice of an emergency beacon slotted intentionally into the air. The USRP X410, sitting quiet on
© 2005 - 2026 AB9IL.net, All Rights Reserved.
Written and curated by Philip Collier / AB9IL.
About Philip Collier / AB9IL,
Commentaries and Op-Eds,
Contact,
Privacy Policy and Disclosures,
XML Sitemap.