Getting Started in the Night
On a clear evening, I opened my laptop and launched HDSDR with the Airspy R2 connected via USB. The receiver’s 78 MHz bandwidth and a maximum gain of 70 dB gave me a familiar sensitivity that felt almost like breathing to wireless enthusiasts. I switched the tuner to the 144–148 MHz band and slammed the gain knobs until I could taste the whispers of distant operators.
Hunting the WSPR Traces
WSPR, or "Weak Signal Propagation Reporter," is a quiet nocturne that slips through the night airwaves, hoping to be answered by another station, anywhere in the world. The protocol uses single-frequency transmissions in narrowband passes; most nets default to 144.390 MHz for the 2 m band and 435.133 MHz for the 70 cm band. A few hobbyists also play around with 135.7 kHz on 2 m and 7.2 kHz on 70 cm, but the standard 144.390 and 435.133 remain the most common voices.
I set the Airspy’s center frequency to 144.390 MHz and the low-pass filter to 30 kHz, a bandwidth sufficient to capture the full WSPR symbol stream. In the same way I tuned to 435.133 MHz for 70 cm, tightening the filter to 25 kHz. The sampling rate was capped at 128 kps, enough to keep the subtle tones, yet low enough to run on my laptop without spitting out data faster than I could read.
Listening for the Gently Whispering Digital Footprints
With the scope open, I listened for the faint burst that appears every 10 seconds. The WSPR signal is a 2 kHz-wide, 50 Hz-BPSK modulated pulse. That pulse coupled with a digital tone bearing the station’s callsign, power, antenna height, and the network coordinate. Because the Airspy R2 shifts its center frequency smoothly, the oscilloscope feed never cursorily jumps; instead I could follow each faint signature as it slid across the 2 m band.
“I’m at 144.390 MHz, looking for something with a call like VE3XYZ,” I typed into the console while the receiver stood silent. After a couple of minutes the monitor flickered—something like VE3XYZ 1 99 N10E08. The network logged the call, recorded the signal-to-noise ratio, and decided whether the reception quality was acceptable. The Airspy R2’s low system noise figure kept the signal-to-noise ratio at respectable levels, even through the quiet suburban skies.
Adjusting Where the Space Shakes
Every radio band has its own quirks. At 435.133 MHz on the 70 cm band I found the bright, high-amplitude noise floor from local repeaters. By adjusting the gain setting to around 32 dB instead of the full 70 dB and applying a sharper filter, I managed to isolate the WSPR pulses, which rose just a few volts above the noise. The Airspy’s IF noise floor wasn’t a problem; it was simply a matter of picking the right band-edge filter and the correct gain.
Why the Airspy R2 Sings in the Night
Because the Airspy R2 is a software-defined radio, the entire fidelity from the front‑end to the digital backend is controlled by code. I could quickly reconfigure the receiver, experiment with harmonic rejection filters, or test at a different bandwidth—all at the press of a key. When the next WSPR burst came in, I could look at the decoded log and furnish the network with a fresh point in a world map. The band look, the receiver configuration, and the patiently steeped monitoring disciplines all coalesce into a quiet, quiet story—one that only a few nights, during the soft glow of city lights, will be able to fully appreciate.
When the Airspy R2 Opens a New World
On a quiet evening the Airspy R2 sat quietly behind a stack of old rubber gaskets, its shiny aluminum case reflecting the dim office light like a small satellite. The first time I plugged it into my laptop, the software gave me a real‑time waterfall that seemed to breathe. I knew I was about to step into a new realm of radio listening, and I was ready.
The First Glimpse of the WSPR‑15 Signal
I set the receiver to roam the 10–30 MHz range, a range that covers almost every amateur free‑band. As the spectrum viewer filled with the soft hiss of distant TV Doppler and the occasional burst from local private repeaters, the Hamming window of the Airspy sharpened my focus. Then, over at frequency 14.092 MHz, a faint shape began to form—a narrow, stable stripe fifty‑kilo‑hertz wide, pulsing in a sequence that looked like a message being written in the sky.
This was the WSPR‑15 signal—amateur radio’s whispered plot for verifying propagation. In contrast to the “classic” WSPR band around 14.244 MHz, the 15 designation refers to the 14.09 MHz primary frequency, offset by about 12.5 kHz down from the center. The network’s standard protocol places a transmitter at a nominal frequency of 14.092 MHz and a receiver at a slightly lower frequency, typically 14.079 MHz, so the pair can be tuned by a lightweight offset.
Emphasizing the Frequency Dance
Using the gqrx front‑end on Linux, I locked the 14.092 MHz channel and let the waterfall scan its surroundings. Every ten minutes a packet emerged—a burst of 930 baud data, a chorus of chirps repeating every 100 seconds. The Airspy’s wide dynamic range let me see the signal’s subtle rise and fall, while the automatic gain control cycled the antenna input just enough for clarity without clipping. I slowly lowered the gain, letting the faint WSPR‑15 whisper float into view as if it were a distant lighthouse turning on at dusk.
Why the 15 MHz Band Matters
Amateur radio enthusiasts favor the 15 MHz band because it often strikes a balance between long‑distance daytime propagation and efficient skywave conditions at night. By monitoring this “WSPR‑15” segment, operators can confirm whether a link to a distant repeater makes sense, or whether atmospheric conditions predict a quiet horizon. The Airspy R2’s excellent stability and low noise floor make it ideal for picking up the tiny signatures of these WSPR packets, which carry little data but huge information on the state of the ionosphere.
My Growing Routine
Each night I now turn the Airspy over to the 14.000–14.200 MHz window, letting the WSPR‑15The Quiet Arrival of the Airspy R2
When the summer sun slipped behind the hills, I finally placed the Airspy R2 onto my desk, its sleek copper skin gleaming under the desk lamp. The little box hummed softly, a promise of waves waiting just beyond the horizon. I opened my favorite SDR client and felt an almost cinematic shift as the tuner jumped to the very first of the long‑wave handful of amateur radio frequencies.
Calibrating the Lens
I set the center frequency to 7.030 MHz and adjusted the bandwidth to 5 kHz, the exact width that the FT‑8 code sweeps across your spectrum. The Airspy R2's 62.5‑MHz analog front‑end leaked nothing, keeping the noise floor low enough for the faint whir of the demodulated bursts to come through. Because the R2 allows programmable gain stages, I dialed the variable gain to stop the tones from clipping without drowning the quieter stations.
The FT‑8 Ballet Across the Bands
Once the tuner was happy, a soft grin crossed my face. I let the receiver roam along the 14‑MHz band, gliding from 14.240 MHz to 14.245 MHz, each 4‑second packet arriving like a postcard from an observer on a distant ridge. I heard the same choreography repeat on the 21‑MHz band between 21.240 MHz and 21.245 MHz, and again on the 24‑MHz band across 24.840 MHz to 24.845 MHz. The tight timing of FT‑8, its 40‑dot blocks of compressed data, felt perfectly matched to the sharp spectral cuts that the Airspy R2 could provide.
Cross‑Band Coordination Made Simple
With the R2’s multi‑band capability, I toggled the center frequency to 7.030 MHz, 14.240 MHz, 21.240 MHz, and 24.840 MHz all in a single workflow. The receiver’s onboard filter and my software’s rapid re‑configuration meant that I could chase a single spectrum display as it transported me from the Dog‑leg down to the high‑frequency swaths without a beat of lag. I practiced aligning the time reference of the FT‑8 packets across bands, noting how the 101 ms delay between transmission and reception allowed me to maintain
Getting the Airspy R2 Set to the Frequency
I began by connecting the Airspy R2 via its high‑speed USB 3.0 port to my laptop. The lightweight tablet‑size device made it effortless to dock in the field, while its dual‑band receiver covered the critical amateur ranges from 24 kHz up to 3.6 GHz. After installing the Airspy's free software suite, I launched SdrSharp and selected the R2 as the active device.
To hunt for the elusive OLIVIA signals, I first brushed aside the ordinary 80 m band (3.5–4.0 MHz) and the 40 m band (7.0–7.3 MHz). Instead, OLIVIA occupies a niche within the 21 m band (14.000–14.350 MHz). Within that band the specific frequencies most frequently used are 14.142 MHz, 14.142 MHz, and 14.196 MHz, each carrying different sub‑bands of the OLIVIA protocol.
I tuned the R2 tuners to a center frequency of 14.200 MHz and set the bandwidth to 6 kHz, which allows the Airspy to capture the narrowband signals the OLIVIA modulation scheme uses while filtering out adjacent noise and reclamator bursts.
Listening for the OLIVIA Signature
With a clean 14.200 MHz reference, I ran SdrSharp's FM demodulator and watched for the distinct modulation envelope — a clear envelope with a fill‑in frequency of 480 Hz indicative of OLIVIA's combined sub‑carrier. The receiver’s built‑in Pretty waterfall display exhibited a steady, shallow tone, while the spectrogram revealed a repeating series of spectral lines spaced precisely 10 kHz apart, matching OLIVIA protocol specifications.
While keeping the time‑base locked to a GPS‑disciplined oscillator, I observed a subtle frequency drift that I could attribute to the local oscillator’s temperature variation. Correcting this with the Airspy’s fixed‑frequency offset adjustments left the signal perfectly centered at 14.196 MHz, ensuring accurate bandwidth measurement.
Expanding the Search to Other Amateur Bands
On subsequent nights, guided by the knowledge that OLIVIA is also sometimes re‑broadcast in the 15 m band (21.0–21.45 MHz), I swept to 21.120 MHz. The same narrowband signature emerged again, this time bearing a broader sidelobe at 10 kHz due to the band’s higher noise floor. Still, the signal’s narrow center remained a treasure, and if I readjusted my gain controls I could pull the details out crisply.
The Airspy R2’s capability to soft‑track across the entire amateur spectrum meant that a single tuner preset could dynamically switch between the 21‑m and 15‑m bands, delivering a continuous monitoring workflow. When I added a quick auto‑gain routine to my custom script, the R2 automatically shunted between 7 dB and 26 dB depending on the ambient S‑level, ensuring that even the faintest OLIVIA burst could be recorded cleanly.
Capturing and Decoding OLIVIA
Leveraging the Airspy’s raw IQ dump export, I saved several hours of data—totaling more than 4 GB—onto a dedicated SSD. Using SoX to translate the IQ samples into a baseband audio stream, I fed the result
The Gears Turn
It was a cool evening in late April when the local field‑day was about to begin. I had the Airspy R2 plumbed into the wall outlet and a spare laptop with SDR# waiting in a puddle of static and anticipation. The device, with its miniature, polished casing, promised one thing: the entire radio spectrum from 1.5 MHz to 6 GHz in the palm of my hand. Tonight, I would turn the airwaves into a living, breathing story.
Seeking the MT63 Whisper
The hunt for MT63—an ad‑hoc digital mode popular among ham radio operators—was always a matter of patience. MT63 is a robust, pseudo‑chirp, binary‑phase modulation that could hide on a quiet slice of a band. It often nests on the 2 meter band, perched between 144.00 and 144.50 MHz, or on the 70 centimetre band, between 433.00 and 434.00 MHz. A few seasoned operators would leave a call sign dancing on sample windows at 50.00 to 50.50 MHz for the 6 meter band, or at 222.00 to 225.00 MHz for the 2 meter extension. These are the places I set my eyes on.
I opened SDR#, adjusted the Antenna gain to a gentle 6 dB, and clicked the frequency wheel. With each click, the spectrum shimmered: bands unfolded like curtains, each a potential host for MT63’s whisper. I moved the dial to 144.372 MHz—a sweet spot I found again and again in recent field‑day logs. The raw FFT display hummed with a faint, steady burst, like a distant whisper puncturing the hush.
Listening to the 2‑Meter Serenade
On the 2 meter band, the MT63 bursts were the quiet notes that ticked between other communications. I tuned the IF to 10.7 MHz and increased the FFT size to 1024 points for a clearer picture. A set of HF filters narrowed the display, cutting out the chatter from the adjacent 2 meter and 1 meter bands. The MT63 shimmer surfaced as a subtle ribbon in the spectrum, a narrowband modulation that swelled as the signal moved through frequency.
For the moment, I grabbed a
A Quiet Invitation
It began with a quiet corner on a rainy evening, a tiny yet powerful Airspy R2 tucked beside a laptop, a soft glow from the screen whispering possibilities. The amateur radio field was buzzing somewhere beyond the walls, and it was the PSK‑31 band that called to me.
Tools Set to Listen
The Airspy R2, known for its 32‑bit dual‑channel digitizer, was configured with a 3.2‑MHz bandwidth centered on 14.245 MHz. That gap left enough room to hear the 20‑meter band, where PSK‑31 bursts often sleep between >14.058 MHz and <14.100 MHz. Using GQRX, I set the analog‑to‑digital conversion to 30 Msamples/s, a sweet spot that balances detail with manageable data sizes.
The Frequency Lullaby
PSK‑31 carriers are typically shepherded just above the strict amateur band edges. On 20 m you can hear them at 14.105 MHz, 14.115 MHz, or 14.125 MHz. The 30 m band hosts them at 10.545 MHz, and the 40 m band sits near 7.160 MHz. By scanning from 7.150 MHz to 7.200 MHz with the R2 in passband mode, I caught the whispered “CQ” signals curling in from the East already in crystal clear form.
Decoding the Invisible Language
After setting a 24‑bit effective resolution on the SDR driver, I switched to CubicSDR. The demodulation chain—quadrature detection followed by phase‑locked filtering—converted the squelched tones into raw demodulated frames. PSK‑31’s 31 bps baud dust required a filter with a 1 kHz bandwidth, which I tuned precisely with the Airspy's tunable LO offsets. The decoding software then transformed the tone shifts into the cryptic stream of text we all learn to read on a monitor.
Successive Tones and Quiet Victory
Horas after, I found myself listening to a dispatch: “CW 10.545 MHz for 4 minutes, then PSK‑31 for 12 minutes while a sailor describes wind shift.” The Airspy R2, with its self‑assembling firmware and open‑source drivers, allowed me to hop between bands without blinking a cord. Every new interception reinforced that the digital world of SDR is as much about patience as it is about precision.
Whispers Persist
Standing before the screen, the Airspy R2’s LED pulsed softly, mirroring the rhythm of a PSK‑31 burst. The story was not just a technical win; it was a reminder that the airwaves above us are a living journal, best accessed with a mix of curiosity, skill, and the right hardware. Every time the rhythmic dots and dashes appear, I know that the future of amateur radio remains open for anyone willing to tune in and listen.
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