Setting the Stage
When I first unwrapped the Airspy HF+ Discovery, the device felt like a portal to the unseen radio ocean. Its sleek dish stared up at the ceiling, as if daring the world to listen to the quiet chatter of ships that whisper their positions over the air. On an ordinary Thursday evening I set the desk on a laptop that had been running the latest Ubuntu 24.04 LTS release, ready to pull the world’s maritime messages into my living‑room console.
Connecting the Airspy HF+
Connecting the USB cable, the system recognized the Airspy HF+ as a new block device almost immediately. The Ardour of the ports humming, I checked lsusb and saw the familiar 0x1d57 ID pop up. From that moment the hardware felt alive, ready to receive the low‑frequency 120.4 kHz band that NAVTEX ships broadcasted each ten minutes.
Installing the Linux Drivers
Installing the native airspyhf driver was a matter of a single memory command. I typed:
sudo apt update
sudo apt install airspyhf
When the package installation finished, airspyhf‑dump appeared in my binary path. The official airspyhf utility could then stream samples directly to a pipe, giving me the raw data stream that could be fed into any decoder I desired.
Capturing the Waves
To capture the 120.4 kHz band I wrote a small one‑liner that told airspyhf‑dump to sample at the classic 48 kHz rate, convert the data to 16‑bit signed little‑endian format, and redirect it to standard output. From there, I piped the stream into the de‑emphasis filter of sox before sending it on to the NAVTEX decoder. The Unix pipe operator made the process feel like a quiet, continuous conversation between the hardware and the software:
airspyhf-dump -f 120400 -r 48000 -b 16 | sox -t raw -
The Discovery of a New Point of View
On a quiet autumn morning, I slipped the slim Airspy HF+ Discovery in my hands, the kind of device that whispers its presence from the back of its PCB. In the hush of the workshop, only the faint hum of my desk fan could be heard. The tiny, blue LED flashed on, settling into a calm rhythm at 100 Hz, a silent invitation to listen to the airwaves in a world where the invisible currents pulse with lives and weather.
Preparing the Digital Heart
First, I opened a terminal and loaded the fresh airspyhf driver so that the Linux kernel could speak the SDR’s native language. With sudo apt install libairspyhf0 the device was immediately visible in lsusb, a tiny token of the gateway opening. Next, I installed a graphical demodulator, CubicSDR, which felt like buying an eager translator that could interpret the encoded RNA of the sky into readable signals. During the setup I paced through the settings, selecting the HF+ as source, adjusting the gain ladder, and pinning the tuner to 17.6 MHz, the region where the most life‑generating weather fax traffic often swims.
Listening to the Weather’s Call
With the hardware ready, I tuned to 17 MHz and watched the waterfall. In the low‑frequency envelope emerged what I thought were random frills, but then a steady whistle appeared. It was a WEFAX transmission, rolled out from the transceiver in a distant weather station. My system was recording the stream at 48 kHz, and I shimmered with curiosity at how a million taxis of data would travel as a finger‑taped, scanned image of the sky.
From Raw Waves to Reconnaissance
The next step was to channel the raw audio through a chain of open source tools that would clean, reformat, and, ultimately, decode the weather fax. I pipe the audio from CubicSDR’s output straight into sox to trim silence and enforce a 16‑bit linear PCM stream. That live stream was then fed into gr-efax, an elegant software defined radio subnetwork that has been optimised for WEFAX decoding. The only command that felt like a spell was:
sox -t raw -r 48000 -e signed -b 16 -c 1 - -t wav - | gr-efax -.
As the signal rippled through GNU Radio blocks, I watched the demodulator convert raw FM into a clean data channel, and the de‑scrambler turn the binary into a monochrome bitmap.
Seeing the Weather Built from the Air
I tossed a screen in front of a monitor that would proudly present the decoded page. The fax filled the screen: columns of ridged numerical tables, the steadily shifting gradients of cloud ceilings and weather cell heights, and, just above the bottom line, a meticulous paragraph detailing the forecast set for the next 48 hours. The image resolved so crisp that I could read the code 8 at 15 kHz that denotes the centre of a constitutive current system. It was as if the sky had handed me a paper map of tomorrow’s rain.
Refining the Echoes, Celebrating the Results
To polish the decoded images, I wrote a quick Python script that wrapped Pillow and took the TIFFs generated by gr-efax. With a couple of lines, I inverted the colours, reduced noise by a Gaussian blur, and exported the final PDFs. With every new WEFAX transmission captured, the archive grew—bits, clouds, echoes of the weather cycle captured in a hands‑tuned Linux environment.
When the Air Spoke to Me
ℝunning an Airspy HF+ Discovery in Linux was more than a technical experiment; it was a conversation with the atmosphere. With each decoded fax, I felt a step closer to understanding the world beyond the weather station’s antenna—a narrative written in rainfall and sunshine that I could read in pixels, with only a simple SDR and the network of open source software to translate it for me.
It was a quiet Saturday morning when the package arrived, the package that would open a portal to a whole new world of signals in the vast sky above us. The box, unassuming but heavy, carried the Airspy HF+ Discovery SD, a little machine that might just become the key to watching storms roll across the globe in real time.
The Arrival of the Airspy
I peeled back the tape and found the device perched on a foam pad, its polished front face reflecting the room’s lights. The packaging came with a small white USB cable, a glowing hint that the hardware was ready to work in unison with its software companion on Windows. No fuss, no lorem ipsum; the instructions were concise, almost poetic in their simplicity.
Unboxing the Airspy
After a quick power reset and a few checks on the Windows Device Manager, it was time to explore the interfaces. I inserted the USB cable into a free port, and the Airspy was instantly recognized as an SDR 2.4GHz receiver. The driver installation was a mere click away, and the software that followed was the SDR# client, a lightweight yet powerful platform for signal acquisition and demodulation.
Configuring the Software
Windowed on my desktop, the SDR# interface opens like a cockpit for the invisible waves. I switched the tuner to 12 MHz bandwidth, the recommended range for VHF low-band signals, and adjusted the device gain to a moderate level. Then I launched the new WFP (WEFAX Preview) plug‑in that had just been updated yesterday by the community, a module that streams decoded fax images directly into a viewer. The interface greets us with a vibrant spectrum display.
Tuning to the WEFAX Frequency
WEFAX arrives most often on 181.5 kHz on the LF band, a modest tone in the chaotic tapestry of VHF. I typed “181.5 kHz” into the tuning bar; the spectrum lights up, a steady hum resonating through the Airspy’s antennas. The Signal to Noise Ratio climbed to a healthy +12 dB, a clear sign that the storm’s whisper was strong enough to travel across the landscape to my static‑free listening post.
Decoding the Fax Image
With the tuner fixed, the WFP plug‑in sprang into action. I watched as the raw transmission began picking up; the synchronous burst of data blossomed into a tiny block of fax resolution. The software demodulated the phase‑modulated signals into a bitmap that unfolded in the preview window, line by line. I could sense the satellite input pulses whizzing past by the way the image flickered, slowly revealing cloud‑scattered us from coast to coast.
Fine‑Tuning the Reception
At first the image was a blur of noise, but I experimented with the Boxcar Filter width and the Synchronization offset. Small adjustments in the 20‑ms segments across the time axis cleared the jitter, and the gradually clearer depiction of the storm’s spray filled the screen. I let the software finish a full scan cycle, and the final output was a crisp WEFAX image, filled with suns and clouds, with arrows showing wind direction and numbers that read the rain rate.
Reflecting on the Experience
When the last line faded, I paused, realizing that the Airspy HF+ Discovery was not merely a piece of hardware; it was an invitation to a place governed by atmospheric physics and signal theory. The WEFAX lesson was wrapped in digital waves that journeyed from digital satellites to my computer screen, and there was a quiet thrill in watching the world’s weather unfold, pixel by pixel, right in my living room.
The Arrival of a Quiet Signal
It was a clear, mist‑laden morning when a young marine technician named Alice heard the faint crackle of a distant radio. She followed the pulse and discovered it was a NAVTEX broadcast coming from a nearby harbor—a vital safety message that guided ships safely through narrow channels. Curious, Alice decided she would learn how to capture that signal on her Mac with an Airspy HF+ Discovery.
Choosing the Right Gear
After spending months in online forums, Alice chose the Airspy HF+ Discovery because of its compact size and wide HF–UHF coverage. What she also needed was a friendly user interface for macOS. She downloaded Airspy Desktop Control, the official Mac application, and CubicSDR, a cross‑platform SDR stack that runs smoothly on macOS Catalina and later. With her Airspy plugged into a USB‑C power adapter, the device immediately reported a fresh firmware version that included enhanced support for digital modes, making it perfect for decoding the TDMA‑based NAVTEX format.
Setting the Stage on macOS
Once the software was up and running, Alice opened CubicSDR and selected the Airspy HF+ as the input device. She configured the receiver to the 18 MHz band—NAVTEX transmissions typically occupy the 18.1 kHz channel grid—and set the gain to medium to avoid clipping while staying sensitive to weak signals. In CubicSDR’s menu she chose the “Band Pass Filter” presets, then toggled the console display to power‑scaled audio for a linear view of the spectrum. GUI knobs were already set to their default values, so she could focus on listening without extra fiddling.
Listening to the Morse‑Like Pulse
The Airspy’s antenna was a 2.4‑meter dipole hung near the roof of her office. As Alice tuned to 18150 Hz, the soft thump of NAVTEX CRACKLE began to dance across the spectrum. In the CubicSDR wave window, she could see the characteristic first‑order one‑bit manifestation of the baseband decoded pulses: the arrival of a 2‑second burst followed by a 0.6‑second silence, repeating at the 4‐second NAVTEX frame rate.
Decoding the Messages
To transform the raw waveform into readable text, Alice used the open‑source tool Chapter 1: The Discovery
When the thunder rolled over the hills and the sky flickered with unseen signals, I found myself staring at the Airspy HF+ Discovery humming quietly beside my Mac. The little dongle, barely the size of a deck of cards, promised endless possibilities. My curiosity, ever restless, nudged me toward an old network thread from March 2024 where a group of hobbyists had shared how to pull the ancient art of weather fax—known as WEFAX—into the digital age.
Chapter 2: The Journey Begins
My first step was to ensure the Mac itself was ready. The Airspy HF+ Discovery talks to the computer over USB-C, and macOS 13.4—or later—ships with a robust USB kernel that can handle the 30 MHz bandwidth the device offers. I downloaded the latest Airspy firmware from the Asterix website, a swift binary tailored for macOS, and flashed it right into the device. When the light on the back winked green, I knew the hardware was humming.
Chapter 3: Bringing the Steam to the Screen
For soft‑soldered SDR platters and a friendly interface, SDRangel dealt the best cards. The open‑source application, now available on 64‑bit macOS builds, makes the process almost poetic. After launching SDRangel, I selected the Airspy HF+ Discovery as the input device and tuned the frequency range to 150 kHz—right into the heart of the WEFAX band that carries those flickering storm charts. The main screen filled with a waterfall display that swayed with the universal heartbeat of radio, and beneath the waterfall a spectral density graph sprinted across every Hz of interest.
Chapter 4: The Language of Weather Fax
WEFAX packets sail on the 2.5‑MHz channel, each packet carrying a 300‑by‑240 pixel image of the sky, encoded in a compressed 640‑bit format. The decoding was the real art. I opened a terminal and ran faxrx, the open‑source WEFAX decoder that sits comfortably on macOS via Homebrew. Feeding it the live stream from SDRangel through an ffmpeg pipeline, the program sat there, waiting for a breathe of data. When the first packet landed, the screen blossomed with a weather map: a cloudy silhouette of the Atlantic, arrows denoting wind, and a faint outline of a tropical maze. The moment felt like a small victory, a quiet triumph over digital silence.
Chapter 5: Fine‑Tuning the Experience
To catch the slow, twisting storms that cross the East Coast, I had to dance with the receiver’s settings. I increased the bit‑depth to 32 bit in SDRangel, turned on the built‑in low‑pass filter centered at 2.5 MHz, and gentleed the RF gain to avoid over‑breathing. In faxrx, I tweaked the threshold for packet detection. The little adjustments turned a jagged, garbled image into a crisp line of canvas, revealing the minimum cloud cover in a crisp blue sky.
Chapter 6: A Digital Archive
After countless scans, I began saving the live WEFAX streams. Each file, stamped with the UTC timestamp of the reception, became a tiny archive of weather history. Over time, I could piece together a chronicle of a season: an avalanche of cloud over the Rockies, a slender jet stream tomahawk over the Pacific, or a gentle drizzle that orchestrated the calm of a midsummer evening.
Chapter 7: The Community and the Future
The last months of 2024 saw the WEFAX community push the limits of decoding speed. A new version of faxrx now supports GPU acceleration on macOS, shifting the heavy lifting from the CPU to the discreet Apple Silicon. By pairing that with the pristine audio quality of the Airspy HF+ Discovery, we can now capture weather fax in real‑time, archive it, and even feed it into a little server that updates a webpage for anyone, anywhere, to see the dance of weather on the spot.
So every time thunder echoes over the hills and clouds stack like waves, I pick up the Airspy HF+ Discovery, let it wander in the sea of signals, and watch the skies gossip through a weather fax decoded right on my Mac, a quiet testament to how technology breathes life into the slowness of old analog, when modern curiosity knows how to listen.
This evening, as the twilight folded its cool shadow over the quiet countryside, I embarked on a new adventure with my Airspy HF+ Discovery. The little device, tucked in its sleek aluminum case, promised a doorway to the skies—a portable radio transceiver with a bandwidth that stretched from 9 kHz right up to 1.3 GHz. My mission was clear: tune into the weather satellite downlinks that traverse the clouds, broadcasting images and data of our ever‑changing atmosphere back to Earth.
Setting the Stage
Before the first tone could hiss through the headphones, I had to acquaint myself with the HF+ Discovery’s interface. After flashing the latest firmware—2024.3.0, released by Airspy to improve the 400‑MHz band’s C‑band performance—I spun the device’s *MODE* dial to “RF DO ” and set the NOISE FLOOR slider to a gentle half
Setting the Scene
It was a chilly morning when I first held the Airspy HF+ Discovery in my hands, its sleek black chassis humming with quiet anticipation. As a hobbyist with a growing interest in aviation weather, I had heard whispers of the VOLMET stations—those intermittent broadcasts that pilots rely on to keep their course safe. I wondered if the tiny radio could help me pull that data out of the airwaves.
Discovering the Frequency
I opened my favorite SDR software, usual friends like SDR#, and clicked on the HF+ unit. The software instantly displayed a spectrum sweep from 0 to 30 MHz. I knew that Volt meteorological broadcasts typically reside in the 4–16 MHz range. The faint hiss of background noise was barely noticeable until I tuned to 8 MHz. There, the silence gave way to a recognizable carrier, steady and clear, waiting for a signal to arrive.
The First Contact
With the filter set to 2.4 kHz, the carrier line appeared bright against the muted background. I used Fldigi connected to the Airspy, running its DIFTYPE=3 settings to pick up the Ringlows’ FM broadcasts. The software demodulated the waveform and fed it to my computer’s headphone output. A voice—warm, authoritative, clocked at 2 minutes 30 seconds—unveiled the speed and bearing of a wind current, the exact altitude of the aircraft, and a trail of current minute-by-minute updates.
Decoding the Data Stream
Voicing clear, yet in jargon, the common HQ designations such as QNH (altitude) and TAS (true airspeed) appeared. To understand the raw packet, I examined the data by toggling the Debug mode in the SDR output. The symbols matched the standard VOR data format, and I found the VOLMET description on volmet.org. With a quick script I could translate those raw bits into a readable table—all in real time.
Beyond the Horizon
Encouraged, I tuned to 12 MHz to pick up a different station. The patience of the HF+ Discovery ARM brought me the same quality of signal. I realized that the Airspy’s high‑resolution ADC and wideband RF front‑end were essential for sniffing these faint, low‑frequency broadcasts.
Optimal Setup Tips
In a relaxed tone, I gathered my thoughts about what worked best. Use a low‑noise amplifier near the antenna to boost weak signals, adjust the gain slider in the software to sharpen the carrier while avoiding clipping, and keep the Airspy’s gain fixed to avoid drifts during long listening sessions. Most importantly, pair the device with an ICOM compatible antenna, as their center frequency accuracy aligns with the HF+ Discovery’s fairly precise calibration.
A Final Thought
With each broadcast I heard, I felt closer to the skies. The Airspy HF+ Discovery turned my living room into a portal to the endless tapestry of weather information that pilots trust every day. The device’s tiny size belied its powerful capacity, and the simple act of tuning turned into a daily ritual of exploration, a connection that bridged my curiosity with the wind itself.
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When the Waves Began to Whisper
It was a cool Thursday morning, the kind where the sea sits like a vast black mirror and
every drop of mist trembles against the glass of the small studio. I had finally unboxed my
Airspy HF+ Discovery, a handheld radio that promised the world of frequencies from the
lowest cracks of the low‑frequency band to the far‑flung reaches of the maritime VHF range.
The unboxing was a ritual—opening the box, pulling the gently wrapped SDR, watching the
little display awaken, and connecting it to my laptop with the provided 90‑degree USB plug.
Learning the Language of the Sea
The first days were all about listening. I tuned the Airspy’s front‑end to 42 MHz, the
classic VHF maritime band used for voice conversations between vessels. The SDR’s
12.4 kHz bandwidth gave me the clarity needed to distinguish weather reports, distress
calls, and the faint chatter of tanker crew. The device’s high‑resolution 24‑bit ADC
rendered the noisier portions of the spectrum into distinct, digitized sound that I could
further process with SDR# and gqrx. The ability to zoom in on a 140 kHz slice
of the band let me capture the NAVTAC broadcasts that seep in from coast‑guard
stations across the Atlantic, their sonic fingerprints unmistakable once isolated.
From AIS to Autonomous Ocean Keeping
In late 2024, the Airspy team released a firmware update that unlocked direct sampling
for the 138 – 174 MHz band, a gateway into Real‑Time AIS (Automatic Identification System)
traffic. I applied the new firmware overnight, and the next morning the SDR resonated with
a dense stream of AIS packets humming through the air. Using the open‑source dump1090
fork tailored for SDR+, I turned raw packets into a live map, watching ships glide across
the visual tapestry with identities and speeds. The data stream was so clean that in just a
week I was exporting the craft’s data to a local database, feeding it into a simple
machine‑learning model that flagged anomalous speeds or course deviations—essentially
building my own marine traffic monitoring watchtower.
Monitoring the Quiet High‑Frequency Chorus
The Sea is a high‑frequency chorus of signals: long‑wave maritime navigation aids, radio
navigation services, and weather reports. The HF+ Discovery’s generous 30 MHz
sweep bias allowed me to dip into the 4 – 8 MHz band where the EDSB (Emergency
Damage Statement Broadcast) is transmitted by vessels after a collision. By setting the
inlet in the SDR# “HF” preset, I listened for the distinct 2.4‑kHz tone that opens an
EDSB transmission and recorded its entire duration—often a critical capture for maritime
accident analyses. After the initial capture, I cross‑checked the signal’s timing against
the NOAA's ARRL logs, ensuring my recordings matched the global.
Fine‑Tuning the Software for Marine Radio Frequencies
The Airspy community has been generous with virtual gear. Among the recent releases are
the multiband slicer plugin for GQRX, which natively supports a 3‑band mode that
automatically isolates VHF maritime voice, AIS, and HFWARNING. The new plugin includes an
auto‑calibrate routine that reads the signal strength over a sweep and adjusts the
local oscillator offset, providing consistent 1 dB margin across all bands for continuous
protection against strong spurious emitters. I logged each adjustment to my training log,
noting the start and stop times of each station as part of my surety protocol.
The Story Still Goes On
With each passing tide, the Airspy HF+ Discovery becomes more than a piece of gear. It is
my window into the river of light waves that bus the ocean floor, a sensor that can
answer questions about ships years ahead, a recorder that gathers signal evidence for
maritime safety investigations. In the quiet of the evening, as the sky turns violet,
I sit on my porch
The Setup
In the early hours of a clearing November night, I slipped my Airspy HF+ Discovery into its little wooden case and carried it across the city’s silent streets to the abandoned rooftop that overlooked the highway. The metal fire escape, once a conduit for commuters, had become the new listening post. I attached a dual‑band VHF/UHF whip to the SDR’s SMA port and fed it to the charging cable that also powered the unit. The HF+ Discovery, with its built‑in RF‑processor and powerful internal antenna, was already humming in the background, prepared to dig through the high‑frequency sky.
First Flight Over the Atlantic
On the first night with the air traffic control frequencies active, I tuned the discovery to 118.8 MHz. A low‑pitched chatter rose from the Dix‑Marine area control tower, the one stepping between the end of the Great Lakes region and the open ocean. The signal was faint, but the Airspy’s software‑defined filtering allowed me to isolate the voice of the controller from the noise of passing weather radars. I captured the slice of high‑altitude fly‑by: an Airbus A330, traversing the Atlantic in a straight line while the controller mandated clear‑air separation and the aircraft acknowledged at 120–125 Hz.
Capturing VHF Air Traffic
Translating voice streams into readable text was one puzzle, but the real intrigue lay in capturing the aircraft’s own transmissions. Using the ADS‑B+ mode II/III packets that the Airspy could pull from any aircraft transmitting on 1090 MHz, I listened to the pulses of data that travel 90 kilometers from the plane into the sky. The sky‑fire of 1090 MHz pulses blurred above the horizon, a constellation of timbres each representing a unique flight number, altitude, and heading. The discovery’s gridded software dynamically adjusted the bandwidth, letting me flag each 20 MHz burst with my own scanner.
Decoding ACARS and ADS-B
On the following nights, I added a 144 MHz receptor, the carrier of ACARS messages. These text‑based fragments, transmitted automatically by the aircraft's avionics, drifted across the radio's delicate strip. One message read, “We are five minutes past the scheduled arrival for KJFK.” Beneath the noise, I could see the BEACON keep-logs: the flight's status, fuel load, the official pulse of the crew’s voice. In the moments after a sunshine burst, the Acars message burst in sympathy: “Mayday, we are experiencing an uncontained engine failure.” These signals, often just a few bytes long, are marked as critical by the aviation community; hearing them, I felt a pulse of adrenaline across the sky.
Challenges and Triumphs
At times the airwaves became crowded. Weather radars and high‑frequency unlicensed users layered across the spectrum, rotating like a sudden storm. The Airspy’s programmable demodulators kept the important aviation signals separated, like a vigilant steward escorting the aircraft on a long over‑water flight. The triumph came when, after years of experimentation, I managed to capture a single VHF sentence from a plane crossing the horizon at 43,000 feet: “Air Traffic Control, this is Flight 1423. Requesting oceanic clearance, altitude 36,000 feet plus 200 feet.” The single line of words, clear over the hiss of a distant storm, sounded like a message from the sky itself.
What’s Next
The journey has only just begun. With the latest firmware updates, the Airspy HF+ Discovery now offers an onboard scrambler that cracks the narrowband codes of each aircraft’s VHF transponder. By refining the capture of the NEX‑RAD? I also plan to dig into the 121.5 MHz RDS / Emergency Squawk? The oceanfront sky has become a canvas where I can trace the movements and messages of thousands of aircraft, turning each listening session into a living map of the world’s air traffic.
Setting the Stage
When the wind chill in the cabin of my mobile radio shack grew sharp and the horizon seemed to melt into a single cloud‑shrouded ribbon, I tuned my Airspy HF+ Discovery back into the air. The device had been a gift from a former colleague, a silky‑smooth, USB‑connected SDR that could take the darkest, far‑away frequencies and translate them into tones that my ears could actually hear. This time, the target was not the usual traffic of LORAN or ham radio dimples, but the far‑flung whispers of aircraft calling home via the INMARSAT network.
Research Meets Gear
It had been a while since the last firmware update that added dual‑band MCRU support to the HF+ Discovery. The 2024.1 revision, released early this spring, re‐tuned the onboard PLLs and tightened the ADC performance, allowing us to sit precisely at 137 MHz with a ±30 kHz capture range. With that precision in hand, I opened SDR# one clear evening, and the world of satellite voice unfolded like a book of secrets.
Tracking the Satellite Voice
INMARSAT’s early‑generation maritime satellites broadcast called‑in voice services around 137 MHz. The aircraft corresponded, for decades, with routine pilot‑reporting formats and unlocked CAP (Common Aviation Phraseology). By sweeping the local oscillator to 137 MHz, I could hear the digital modulation that wrapped every transmission. The Airspy HF+ Discovery turned those whispers into a four‑channel spectrum, and with the help of software “filter banks” I isolated the narrowband voice link from the satellite’s guard-bands.
Describable Details
Because the satellite link uses DIF‑M encoding, the amplicon of the incoming signal masked the pilot’s voice behind a compressed digital carrier. With SDR#’s dynamic waterfall view, I could set the side–band width to 900 Hz, exactly the value that matched the INMARSAT waveform. Once the loop‑back was locked, the transponder’s voice burst out to the receiver as a clear talk‑man and UV-waypoint announcements. An ancillary script ran alongside, logging every decoded ICAO A/DS code to a text file for later analysis.
Practical Tips for Those New to the Scene
1) Get the latest firmware from the project’s GitHub repo—i.e., version 2024.1.
2) Use a dedicated 24‑V to 5‑V USB power supply to avoid signal jitter from the power supply noise.
3) Set the tuner’s “Frequency Tuning” offset to exactly the satellite’s nominal 137.7 MHz; a small error will pull the waveform out of the voice bandwidth.
4) Keep the gain flat; a sudden spike at 20 dB will drown out the delicate burst tones.
5) Finally, watch the secular drift on the satellite’s mid‑week pass; it will shift a few hundred hertz over a 24‑hour cycle.
Into the Echo of the Skies
On a clear night, the sky flickered with the faint glow of the geosynchronous relay. The Airspy HF+ Discovery, quietly humming, captured the faint, predictable waveform as the aircraft’s radio dipped into the satellite’s channel. Every chirp, every confirmation, carried the atmosphere of that remote flight—much like a time capsule held within the cold metal of our device. The reception was so crisp that the voice could be hooked in real time, allowing me to respond with hand signals that the pilot could feel. That night, the land, the aircraft, the satellite, and the software sat together in perfect harmony, a moment of digital and human communication, captured in stillness yet alive with possibility.
It began on a quiet Saturday afternoon when I decided to open the little box that had been gathering dust in my basement. The Airspy HF+ Discovery felt like a relic from the old days of ham radio, yet the promise of coaxing quiet whispers from the skies kept my curiosity alive. I plugged the USB dongle into my notebook, coaxed the antenna to a low‑end dipole, and watched the software greet me with its familiar green interface.
The First Reception
At first, the screen showed nothing but a smooth curve of random noise – the radio world's equivalent of background static. Still, I was determined. I flipped the frequency slider and halted at the 7 MHz mark, a sweet spot for VHF aviation traffic. Then the air crackled, not with a harsh noise but with a faint but unmistakable tone sequence. My scanner, patiently waiting, suddenly sang a clear ACARS message: “C‑1734 pending … ETA 14:32.” I had just dialed into somebody’s in‑flight data. The feeling was electric, almost as if I had just plugged into a channel of the very air that keeps millions of planes on course.
Unlocking the Frequencies
Following the ACARS melody, I broadened the sweep, exploring the range from 10 kHz to 30 MHz that the HF+ Discovery proudly offers. Each frequency sweep revealed a library of digital voices – VDL III packets, aircraft directory updates, and even meteorological broadcasts. The hardware’s 34‑bit ADC let me pick up the thin, narrowband VDL channels with clarity that would be impossible on a conventional S‑band receiver. The UI’s spectrum view helped me line up the carrier while the demodulator was vigilant for the very specific chirp patterns that define these digital protocols.
Decoding ACARS and VDL
It was a day of experimentation, tweaking the signal gain and demodulation settings. Within moments, I managed to capture a complete ACARS “text/plane‑to‑ground” conversation, complete with the aircraft’s callsign, launch code, and weather data. The text appeared in the log window, and for a brief instant, I could see the information cascading like a waterfall of letters. When I tuned to the 18.68 MHz band, a VDL III signal manifested: a looping packet of standardized aeronautical data, again translated give-and-take into plain English on the terminal. The process felt like watching Morse code written by satellites, only the signals were far more precise and far more generous.
Firmware and Software
Between bursts of aviation chatter I discovered a newer firmware update from the manufacturer, version 2.0, announced only last week. The update promises a refined digital‑mod demodulator and a more robust parsing engine for ACARS and VDL packets. In the software, I could step through the decode log, marking key points with the “mark” feature, this lets me correlate the raw audio with the decoded message on the timeline. I also experimented with an open‑source companion library – Gr‑Air, a versatile GNU Radio flow‑graph specifically tuned for aviation digital modes. The combination of hardware, firmware, and flexible software allowed me to collect data continuously over long periods, even capturing rare ephemerality such as a distress ACARS message from a small aircraft on a remote airstrip.
Future Prospects
Every story, no matter how technical, culminates in a "what next" question, and my nights are now booked for that pursuit. The Airspy HF+ Discovery has proven to be a portal, not only to the immediate chatter of commercial airliners but also to the quieter, high‑frequency sweeps where amateur pilots or missile telemetry might whisper through the sky. I plan to set up a data‑logging rig to capture dozens of flights per day, correlating those bits with known flight paths, and maybe even build a custom dashboard that will display the real‑time boom of ACARS and VDL data in a beautiful, web‑based format. The horizon seems as rich and wide as the low‑end spectrum itself, and it all started with a simple click of a frequency and a buzzing of curiosity.
Sparks of Flight
Alex had always felt a pull toward the vast expanse of the radio spectrum. When the Airspy HF+ Discovery arrived in the mailbox, it seemed less like a piece of hardware and more like a key that might unlock the hidden conversations of the sky. The little unit, wrapped in its slick aluminium housing, whispered promise rather than conversation—of a world where ancient analog voices were replaced by crisp digital streams.
Into the Frequencies
Setting up the HF+ was a ritual. Alex first paired the HF+ Discovery with the Airspy AntennaAdapter and soldered a 5 m triaxial feedline to the front. The antenna, a self‑driven low‑frequency loop, sang across the VHF band with a soft thrum that felt almost musical. The next step involved the SDR++ application, which offered a clean interface for tuning, demodulation, and spectral visualisation. The software was updated to firmware 1.5, a version that introduced enhanced DSP kernels capable of handling high‑density digital modes such as HFDL, APRS, and MFSK.
Unveiled Secrets
With the hardware ready and the software freshly updated, Alex tuned to 129.74 MHz, the traditional frequency for HFDL traffic. The screen flickered to life, filling with a waterfall that traced the faint pink‑white sweep of digital bursts. The first HFDL packet emerged—a concise burst of data, followed by a gentle silence that grew into an ocean of voice and telemetry. The SdI‑app, now integrated into SDR++, decoded the bursts into a playback window. Alex found themselves transported into the cockpit of a regional jet: the weight of the flight plan, turbulence forecasts, and ten‑minute updates rolled out as clear, speakable text.
Transmitting the Sky
Curiosity turned into ambition. Alex was not content with merely listening; they wanted to send as well. The HF+ Discovery is equipped with an 8 kHz IQ output, and by feeding that signal into a low‑power 2.4 kHz transmitter with an extra Octal‑band HF+ RF gain card, a modest 1 W signal could be carved into the uplink. In 2026, the HFDL Software 3.2 introduced a “citizen radio” feature that allowed enthusiasts to transmit flight plans and weather pings back into the network, provided the signal remained below the 10 µW regulatory threshold. Alex configured their SDRuno session with a single 44 kHz channel, crafted a test packet, and transmitted: the sky sang back with a short, clear tone, confirming the uplink worked as intended.
A New Chapter
Months later, Alex’s routine had transformed. Each morning they would turn on the HF+ Discovery, slide the knobs, and let the radio fill the room with streams of data from aircraft as far away as airports in the Pacific. The Airspy Hub analytics track – logs of successful HFDL receptions, community contributions, and peer‑reviewed calibrations – fed into Alex’s own catalogue of flight stories. The narrative
Chapter 1: The First Tuning
When I first opened the little USB‑powered Airspy HF+ Discovery, the night air tasted of electric promise. The device, with its sleek black body and tiny fan, whispered that it could turn ordinary waves into a movie of historic radio, even a modern DRM broadcast. All I needed was a Windows laptop, a good grip, and a story that would unfold over channels.
Chapter 2: The Puzzle of Drivers
As the cable hugged the port, the operating system demanded drivers. I navigated to the official Airspy website, downloading the latest Windows package—Version 2.6, released just this spring. Once installed, the device gleamed in Device Manager like a tiny star, ready to dance.
Chapter
Preparations in the Quiet Before the Broadcast
When the first chill of autumn morning settles over the bay, the Airspy HF+ Discovery gleams on the workbench, a silent promise of the hidden radio worlds waiting just beyond the airwaves. After a quick inspection of the connector ports and a fresh USB cable, I plug the device into a macOS laptop that has already been prepped with the latest drivers from Airspy’s official GitHub repository. The system instantly recognizes the hardware, and the little indicator light pulses green, confirming that the firmware is ready for the deep‑sea signal search.
Turning the Airspy into a Gateway
With the device recognized, the next step is to channel it into the software ecosystem I’ll be using for decoding. The authors of the SoapySDR project have made a clean backend for the HF+ Discovery, which manifests as a coherent source in any GNU Radio flowgraph or command‑line tool that can consume the SoapySDR interface. I open brew with the command brew install soapy-sdr soapy-airspy, and the build completes in under two minutes. Afterwards, a quick test with soapy_adc -b 1024 -s 2000000 -c 9200000 shows a steady stream of samples streaming from 9.2 MHz, the typical channel for a DRM broadcast in the FM band.
Setting the Stage for DRM
DRM, or Digital Radio Mondiale, is a surprisingly elegant protocol. It is the digital cousin to traditional AM and FM, re‑using familiar 20 kHz FM band spacing but with compressed audio layers that replace the old cassette‑style audio. To capture it, we need the right sampling rate and demodulation chain. In my case, I selected a 192 kHz sample rate to comfortably capture the 128 kHz of DRM bandwidth plus an ample margin for filtering. In GNU Radio, the flow graph begins with the Soapy Source block set to 192 kHz, followed by a mixing block that centers the signal around 0 Hz, a band‑pass filter that isolates the 20 kHz slice, and finally the goDRM demodulation block.
The goDRM Connection
There’s a rising star in the macOS SDR community called goDRM, a terminal‑based receiver built in Go that leverages the libdrm decoding stack. After installing Go and running go install github.com/StefWork/GoDR
Finding the Signal
When the city lights dim with dusk, the quiet hum of the stars and the hidden chatter of our world become the only sounds that persist. In a nondescript loft perched above a quiet suburb, a seasoned technologist tuned his Airspy HF+ Discovery to the 433 MHz ISM band, a region humming with the digital pulse of remote‑controlled sensors and home automation telemetry. The HF+ Discovery gleamed under the strip lights, its small form factor belied the enormous potential for capturing the minutest of signals across a 1.5 MHz to 6 GHz spectrum.
Turning the Airspy into a Telemetry Eye
He first updated the firmware, downloading the latest release from Airspy’s official repo to ensure the radio’s 24‑MHz sampling capability was operating at peak efficiency. The device was then paired with CubicSDR, a versatile cross‑platform application that supports real‑time demodulation on the Fly. With the spectral view bleeding into a dense sea of points, the 433 MHz channel was highlighted—a subtle spike that betrayed the presence of a packet of irony or a weather station’s silver data burst.
Capturing the Pulse of the 433 MHz Worlds
A dozen thousands of smart devices lie in that band, each ticking its heartbeat in the form of very‑short, often non‑enveloped packets. An up‑to‑date example, recorded in late 2023, was a tiny LoRa‑based environmental sensor broadcasting humidity and temperature values every 30 seconds. The HF+ Discovery captured the bursts with such fidelity that a simple script using libsdr and the lora-packet-decoder library turned the noisy sea of tones into a string of intelligible JSON messages.
Eavesdropping on Home Automation
There was also a popular open‑source device, the ESP‑Home based 433 MHz RF controller, that sold in boxes around the corner of every local store. The author re‑played the recorded packets in a test enclosure and confirmed the patterns, noting the clear rise‑time changes when motion sensors toggle. While the hub in a living room waited for these transmissions, the HF+ Discovery listened non‑intrusively and built a timeline of every pulse that translated into a “button pressed” action. The audit, done in 2024, proved that even the private transmissions were susceptible to passive monitoring when the tool is in your arsenal.
Decoding in Real‑Time with One Simple Tool
Rather than diving into a complex stack, many hobbyists, after the firmware upgrade, use the SDR# (SDRSharp) plugin “Raw 0‑band”. A simple toggle to “Airspy HF+ Discovery” streams the raw complex I/Q directly to an Envelope Analyzer where the 433 MHz packets rise like ripples on a still lake. With a preset demodulation of OOK (On‑Off Keying), which is typical of sensor telemetry, the incoming burst patterns become visible in milliseconds. By tweaking the bitrate to match documented standards—38.4 kbit/s for many LoRa Out‑of‑Band bursts—decoded packets appear as readable ASCII on the same monitor.
Story of a Meteorological Data Stream
Imagine the gentle hum of a field station at the edge of a wildfire risk area, each sensor node sending bursts in the early morning. As the wind stirred, the field’s micro‑weather station transmitted a 433 MHz packet describing canopy temperature and wind speed, bouncing off the surrounding hills. The HF+ Discovery, perched on a tripod, captured every packet that flowed through the silent terrain. By running the stream through an open‑source demodulator and then a simple script that calculates the angular displacement using the packet’s RSSI values, the author plotted a raw weather map in real time—an unexpected yet invaluable early warning system.
Concluding the Tale
A few months into full‑time tinkering, the friend now wields the Airspy HF+ Discovery like a pair of binoculars pointing at the in‑visible world of telemetry. The 433 MHz ISM band, once a silent background noise to most, becomes a living print of daily data—smart meters, environmental readings, even the lingering breath of a remote lawn‑mower’s controller. Each captured packet, decoded, and linked back to its source turns the loft into a small observatory, and the hobbyist into an unseen guardian of the electromagnetic heartbeat that runs through the very skin of our modern living spaces.
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Written and curated by Philip Collier / AB9IL.
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