The Cradle of the Cycle
In a quiet studio, where the only constant was the hum of the campus servers, the ADALM‑Pluto Revision D sat on a table, its sleek black chassis a silent promise of discovery. Jane, an enthusiastic *amateur radio* operator, unlabeled the box, pressed the tiny reset button, and the laptop screen flickered to life with a familiar waveform display—her portal into the unseen ocean of frequencies.
Setting the Scene for WSPR‑15
Jane’s eyes wandered over the spectrum, looking for the narrow thread of WSPR‑15. The handbook told her that WSPR‑15 occupies a 10‑kHz channel spread into 15 667‑Hz subbands, each two‑octave wide, across the classic amateur allocations. The key to successful listening was accuracy: the Pluto had to lock onto the exact center of the chosen subband with an uncertainty no larger than a few hundred hertz.
Hunting the 80‑Meter Echoes
Her first target was the 80‑meter band. She adjusted the Pluto’s tuning to 2,406.5 kHz, the official center for WSPR on that band. The narrowband display lit up, revealing the faint Morse‑like pulses Jane loved. She increased the receiver’s gain, shut off the automatic gain control, and listened as the 14‑meter band echoed in its 14,084 kHz location, a perfect mirror in the sky.
Crossing to the 40‑Meter Shoulder
Turning the dial to 7,056 kHz, the 40‑meter band unfolded before her eyes. Each pulse now carried a new story from distant stations. Jane noted that WSPR‑15 on 40 m often topples at 7,048 kHz to keep within the band edge limits, a subtle shift that her spectrum analyzer confirmed instantaneously.
Sailing the Extension Across 20, 15, and 10 Meters
Next she navigated to the 20‑meter isle at 14,040 kHz, and then slipped into the 18,046 kHz domain for 15 m. Each band whispered its own rhythm, a signal weaving through skirmishes of interference. For the 10‑meter stretch, she sleuthed the 28,028 kHz window, recalling that many fresh operators transmit from 28,026 to 28,030 as safety margins, a range vital for locating a faint WSPR‑15 trace.
Charting the 6‑Meter Horizon
A little slower, the Pluto's tuner drifted to 50,030 kHz, where the 6‑meter’s 40‑band overhead extended. Here Jane's screen registered the faint “splash” of the WSPR signal at 50,028 kHz, letting her know that even in a band with limited hours, the Aurora of signals remained bright.
Clearing the Extending 2‑Meter Spectrum
She lingered on the 144,028 kHz slot— her favorite 2‑meter haunt. The phenomenon of WSPR‑15 on 2 m, though narrow, was a dance with time: shift slight to 144,032 kHz to evade the crowded 144‑148 MHz segment. The Pluto, guided by Jane's precise frequency setting, captured the concealed pulses—a testimony to both human curiosity and machine precision.
Field Test in the 70‑Centimeter Realm
She then set the cursor to 432,028 kHz, a region replete with high‑frequency chatter. The RX grid surged with activity, and the WSPR‑15 pulses glimmered faintly at 432,026 kHz, an echo from architecture across the planet that resonated strongly in the long‑wave horizon.
Final Echoes and the Quiet Await
As the session wound to a close and the last notes faded over the screen, Jane reflected on the
New Software, Same Love for the Air
When the new ADALM‑Pluto Revision D arrived in late 2023, I felt the same thrill that I had when the first version of the device first rolled out. The update advertised a more robust firmware core and a wider tuning range, extending from the legacy 300 MHz up to 6 GHz without the need for any external segments. I was eager to test it out, not just to explore the upper bands but to see how it would perform on the quieter parts of the spectrum where the unspoken conversations of the ham world reside.
Setting the Stage
I set the Pluto up on my workbench, attaching a compact dipole for the 70 cm band and a coaxial feedline that brought the 2 m and 80 m bands to my front end. A small low‑noise amplifier sat just before the device, pushing the quiet chatter just enough for my FT‑8 decoder to hear. With the new firmware, the tuner became more reliable when stepping through the fine frequency bars of the amateur bands: 70 cm from 420.300 MHz to 420.750 MHz; 2 m from 144.025 MHz to 144.425 MHz; 80 m from 3.525 MHz to 3.975 MHz; and the 160 m window from 1.780 MHz to 1.980 MHz. Each band lay in its own neat band‑plan, a quiet map of where signals could come from.
Listening to the Quiet Dialect
The first time I tuned the Pluto to 144.265 MHz during a cool November evening, the FT‑8 crackle came through, a rhythm of 45.39 Hz carrier modulated over a 1800 Hz symbol rate. The words—“CQ”, “QSY”, “CQ D…”—sliced through the noise like a series of soft pings. I repeated the process on 420.542 MHz and soon found a steady stream of LOVE messages from across the continent. Each call answered in quick triads, four seconds of data on every 40‑second cycle, and I could see the spectral signatures wash across the spectrogram like the ripple of a pond disturbed by a tiny stone.
Challenges and Small Triumphs
Finding the perfect antenna gain for the 160 m band can be tricky; I balanced the 1.78 MHz–1.98 MHz window with a careful flag of the tuner's internal filtering. When I hit 1.880 MHz, the signal burst into life, echoing the signatures that guided the creeping mountains in Ireland. The Pluto’s new firmware this revision also adjusted the internal knob of the tuner, giving me more stability in the low‑frequency range. That small win allowed me to track a faint QRP “QRP” cornering from the Scottish
First Steps with the ADALM‑Pluto Revision D
We began by connecting the sleek Adalm‑Pluto Revision D to a laptop running GNU Radio. The driver hop was smoother than a new pane of glass, and the software radio interface greeted us with a clean, low‑latency spectrum view. The device’s 30 MHz bandwidth felt like an open sea, and the 30.72 MS/s sample rate promised capture of the finest slices of the HF spectrum.
Going on a Hunting Quest for FT‑4 Signals
The next challenge was to locate the elusive FT‑4 transmissions that hobbyists whisper about—those compressed SHF bursts that pack a lot of data into a tiny bandwidth. The Pluto can be logged into a recording script that samples at 200‑kHz resolution, sufficient to resolve the 3‑kHz wide FT‑4 channel while keeping the jitter low.
Stationary Frequencies to Watch
With the antenna pointed toward the 80‑meter band, the first key location for FT‑4 came into focus at 3510 kHz. The signal rode the common “80 m‑doorway” and hung neatly in the middle of the spectrum slice. The second beacon, more hidden, waited at 4020 kHz, just below the 80‑meter short‑wave niche, offering a quieter listening experience.
Venturing on the 40‑Meter Floor
The 40‑meter band, more congested, provided its own FT‑4 challenge at 7045 kHz. Here the signal scattered like a flock of birds, frequently hopping a few kilohertz up or down. By setting the Pluto’s center frequency at 7050 kHz and letting the narrow‑bandwidth window slide, we captured the curious dance of data packets broadcast in a thin 3‑kHz envelope.
Few Hours, Many Lines of Code
Those few hours of recording, the snippets of code that tuned the SDR, and the transcribing of the decoded FT‑4 frames turned into a long, intimate conversation with the HF spectrum. Each burst felt like a secret message whispered in Morse, but compressed into a much tighter packet. And every time the Pluto’s tuner touched those corner frequencies—3510, 4020, 7045—the spectrum glowed with the warmth of a shared signal.
Reflection on the Journey
Monitoring the FT‑4 band with the ADALM‑Pluto Revision D turned out to be less a technical exercise and more a storytelling arc. We charted a path through the HF treeline, anchored our narrative on fixed frequencies, and followed each packet as if it were a plot point in a radio drama. The result? A detailed tapestry of the amateur radio world, woven with bold signals and italicized moments of discovery, all seen through the clear eye of the Pluto SDR.
Reaching for the Skies
When the next sunrise painted the sky in a soft amber glow, Alex set up the ADALM‑Pluto Revision D beside the window overlooking the town’s radio station. The analyzer’s sleek PCB was humming quietly, a testament to another chapter in the world of software‑defined radio. With a gentle clack, Alex attached the powerful external antenna, aimed toward the horizon, and nearly felt the electric pulse of the universe winding in through the receiver’s crystal‑controlled microchip.
OLIVIA Signals in the Air
The challenge was clear: capture the OLIVIA family of signals cruising through the 80 cm amateur band. Those brief pulses, a multi‑beam experiment designed to test wideband agility, hover just above 360 MHz and glide across the spectrum with up to 20 MHz of instantaneous bandwidth. Near 358.5 MHz one could hear the first squeal of the test pattern, while the bright burst at 363.2 MHz marked the checksum anchor. Alex tuned the right‑hand side (RHF) oscillator on the Pluto to 360 MHz and slyly stepped the frequency offset a few kilohertz at a time, testing every segment of the 10‑MHz slice required by the protocols.
Monitoring 10 cM Adventures
When the OLIVIA team pushed the payload onto the 10 cm O‑band, they demanded operation around 10.100 GHz. The Pluto’s internal tuner cannot reach that high, yet its firmware allows a software backbone that interacts with external upconverters. With an external RF conversion chain, Alex positioned the Pluto’s 115.200 MHz output upstream to a frequency translator, stitching the two devices together in a seamless flow. The end result was a real‑time view of shimmering OLIVIA spectral shells, spinning like galaxies across the radar chart.
Hourly Log of Patterns
During a two‑hour test window, Alex recorded the repeated prime frequencies: 358.48 MHz, 359.02 MHz, 360.00 MHz, all the way to 360.75 MHz for the narrowband “pilot” signal. While the 10 cm test pulsed around 10.164 GHz, its image on the Pluto’s spectrum grew as a narrow spike at the translated 120.7 MHz anchor point, thanks to the external bandpass filter that eliminated the sidebands. The AT‑band always came alive at midnight, causing a gentle hum in the Pluto, a reminder that even a small SDR can feel the pulse of the future.
Reflections on the Glow
In the dim glow of the laboratory, the ADALM‑Pluto Revision D became more than just hardware; it was a temporal bridge that let Alex hear OLIVIA dance over the 80 cm and 10 cm bands. Each frequency became a brushstroke in a living, breathing spectrum, and each burst whispered a tale of amateur ingenuity and the art of signal reconstruction. The story of that evening ended with the Pluto’s LED blinking a soft green, confirming that the network was open, the data stream alive, and the world of amateur radio still beating strong in the hands of those daring enough to listen.
When the Pluto Surfed the Airwaves
It began on a quiet summer evening when the sky was still awake and the radio static sang like distant sea gulls. I pulled the ADALM‑Pluto Revision D from its box, its sleek titanium chassis reflecting the warm hallway lights. The revision symbolized more than a mockingbird’s name; a ripple of firmware, a cleaner analog front‑end, and an engineer’s promise of silence in the band I was about to dive into.
My hexagon‑shaped antenna dangled from a closet hook, a relic of my first family ham radios. I powered the Pluto with a power bank that hummed quietly, and the Linux terminal grew impatient with my excitement. I opened QSignal, set the receive centre to 14.070 MHz, and let the SDP take me to the 20‑meter band.
Decoding the 20‑Meter Pulse
The first whisper on the screen was that faint buzzing of a PSK‑31 signal, 31.25 baud transmissions whispering across the band. The Pluto’s low‑noise amplitude‑modulated filter let me hear the sine‑wave in his tiny 3‑kHz slice—each tiny pulse a message between radio geeks under the same airwave canopy. I noted down the anchor frequency: 14.070 MHz—the most popular spot for 20‑meter PSK‑31, where members strung out a chain of 20‑meter avatars.
When the turnovers became regular, my eyes followed the long‑lived stainless‑steel anchor numbers sliding across the screen where the signal pressed itself. The Pluto’s new revision showed no clipping, no flicker, letting me witness the waveform as a clean brass note.
Swapping Toward 15 Meters
Next I nudged the centre frequency up by several megahertz: 21.050 MHz. The same 31.25 baud rhythmic beat appeared, unmistakably the standard 15‑meter PSK‑31 spot. The story was the same, the Pluto’s spectrum analyzer displaying the band and the voices did not need to trim more. The frequency spelled out the knowledge I had gathered about our favourite PSK‑31 anchor: 21.050 MHz.
Tracing 12 Meter to 6 Meter and Beyond
I did not let the night pass without listening to the still untamed twelve‑meter band. The digital flare flitted to 28.070 MHz, a countdown visible in the waveform lights that glowed like a green fire. Again the Pluto’s picture was crystal: every pulse counted. The fresh recording added 28.070 MHz to the list of hardened PSK‑31 positions.
When the air grew thin enough, the core amplifier effortlessly lifted to the 6‑meter scene: 50.069 MHz. The oscillator vibrated like a well‑tuned violin, a caress of tiny waves arriving at the Pluto’s front end. With ease, I documented 50.069 MHz; my story grew—darker, deeper, even windowless. After the 6‑meter high, the 2‑meter band, slightly above the L band, soon revealed itself. The Pluto, with its modern re‑working, sang the 144.069 MHz PSK‑31 voice, airy and crisp. The frequency placed in my narrative: 144.069 MHz.
Reflection on Revision D’s Quiet Wisdom
Every band, every soft pulse, was a testament to the revision D’s edge—its upgraded mixer tolerances, the cleaned‑noise lens on front‑end, and the firmware that stabilised its crystal oscillator. The Pluto turned a fleeting sweep of radio into a living poem that linked my family’s ham heritage with the present. Each PSK‑31 frequency I noted—14.070 MHz, 21.050 MHz, 28.070 MHz, 50
In the Quiet Studio
I slipped into the dimly lit workshop, the air humming with the faint buzz of the ADALM‑Pluto Revision D resting on the workbench. The SDR’s tiny form factor belied its power; 61.44 MS/s of raw spectral juice lay waiting. My goal was simple yet thrilling—to listen into the high‑frequency fingertips of the amateur band and catch the faint rhythms of PSK‑63 and PSK‑125 communications.
Preparing the Toolkit
First I opened the open‑source SoundWire application and tapped the SDR’s GPIB address. The firmware report confirmed the new revision D’s enhanced analog‑to‑digital chain. I set the sampling rate to 12.288 MS/s, a sweet spot that balances resolution with manageable data streams for the 2 m band. The center frequency for the first hunt was locked to 144.100 MHz, comfortably straddling the 14 MHz ISM band most popular on the 80 meter segment of 2 m. I then dialed the filter bandwidth to 24 kHz, wide enough to cradle the ±62.5 Hz spread of PSK‑125 while keeping out stray noise.
Listening for PSK‑63
With the spectrum window open, a gentle cascade of tones rose on the screen. The classic 63 Hz shift spread its two peaks symmetrically around a carrier—precise and silent when the signal was quiet. The carrier hovered around 144.110 MHz; a quick glance at my log showed that most PSK‑63 operators in this region ping between 144.080 MHz and 144.120 MHz. The frequency offset of ±31.5 Hz is tiny but the signal’s narrow bandwidth makes it a delightful hunting ground for the Pluto, whose ADC resolves sub‑kHz differences with ease. I keyed in the '+' and '-' control to tweak the local oscillator until the sidebands danced in lockstep, confirming I was indeed hearing a legitimate PSK‑63 packet.
Diving into PSK‑125
Once comfortable, I turned the focus to the more demanding PSK‑125. This mode doubles the shift, stretching the spectral footprint to ±62.5 Hz. On the spectrum eye the carrier shifted a touch higher, around 144.105 MHz, and the sidebands thickened into a clearer, more spaced pair. I noticed that operators in the 2 m band usually plant these bursts between 144.085 MHz and 144.115 MHz, a narrow slice that still fits neatly into my 24 kHz window. The Pluto’s SDRbox still handled it gracefully; its PLL held steady even as I nudged the center frequency to track the signal’s wander. Each PSK‑125 packet was a brief burst—often a poem of telemetry—never exceeding a few hundred milliseconds, a testament to the efficiency of the mode.
Drawing The Horizon
After hours of scanning, I plotted the distribution of the two modes on a simple spreadsheet—always keeping in mind that the ADALM‑Pluto Revision D could capture more if I widened the bandwidth
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