Into the Quiet Spectrum
When the evening light began to fade, the old ham table glowed with the low‑power LED of the Airspy HF+. Its rubber case smelled faintly of copper, and the single button marked SCAN was set to the slowest speed, so the receiver would lecture the sky gradually instead of shouting over a chaotic radio sea.
Adjusting the Tuning
The receiver’s dial moved, inch by inch, as the operator flicked through the amateur radio bands that had come to carry the quiet, granular FT-8 exchanges. At 1.8 MHz the interference from the city’s electric lines lurked like a buzzing bee, while at 10.7 MHz the hum of distant traffic vanished, leaving a crystalline empty space. The tuner was set in 100 kHz steps; each interval was a small window into a different part of the ether. The important frequencies, highlighted by the FT-8 protocol, were: 1.823 MHz, 3.571 MHz, 5.311 MHz, 7.301 MHz, 10.703 MHz, 14.101 MHz, 18.104 MHz, 21.011 MHz, 24.890 MHz, and 28.520 MHz.
Listening to the Messages
When the scanner settled on 14.101 MHz, the soft whisper of a single phoneme erupted from nowhere. It was the solitary “CQ 73”, a polite call announcing the presence of a ship‑board operator ready to play the alphabetic game. The operator pressed MENU and selected FT‑8 Decoder, allowing the software to interpret the 15 Hz tone and the 175 Hz burst that followed. The decoded text appeared, momentarily in bright green, and then disappeared with the fading overtones.
Why the Focus Matters
In the narrative of a busy spectrum, the Airspy HF+ was the quiet eye letting the user find stories buried in the layers of the HF band. By meticulously stepping through each 100 kHz interval one could hunt for the sparse but reproducible patterns of the FT‑8 protocol. The meticulous frequency list helped to keep the search concise and efficient, saving the operator from a random and chaotic listen‑and‑hope approach.
The Dance of the Data
Each moment on the sky was a whispered conversation, a little story of one hand to another. And though the halo of the receiver’s LEDs pulsed in the background, it was the soft, spectral plaque of the FT‑8On the Edge of the Spectrum
I"ve spent the last few months listening to the quiet hum of the night sky, the faint squall of distant stations, and the vibrant pulse of the FT‑4 band. The Airspy HF+ has become my window, a small, unassuming device that opens a wide world of signals to my ears.
At first, the band felt like a darkened forest. The HF+ was guided by the new firmware release of 2024 that lowered the noise floor by two decibels, making the faint whispers of 440 MHz now appear as if they were speaking directly to me. The HF+ can capture 402–450 MHz on a 30‑MHz wide IF, thanks to an external tuner and a carefully chosen bandpass filter. That means I can now hear the FT‑4 band with clarity that was only dreamed of in my early trials.
Finding the Line in the Noise
With the new audio interface, I developed a simple workflow: I sweep 440–445 MHz, letting the Airspy HF+ feed the data into my SDR software. The software splits the band into 10 kHz slices, and each slice is stacked in a spectrogram. In that stacked
Setting the Stage for the Airspy HF+
When Olivia first slipped a faint melody onto the 15‑meter band, the 21.23 MHz window became a kind of secret gate. To open it, I slid the Airspy HF+ out of storage, leaned it against my laptop, and let the tiny dongle breathe out its 120‑kHz bandwidth in the band that Olivia chose. The first four hours were a quiet exploration of 10‑, 20‑, and 15‑meter psychology, but by the time the sun dipped behind the mountains, the signal burst to life on 21.23 MHz (USB).
Why the Airspy HF+ Is the Ideal Companion
The HF+ is no ordinary SDR. It sports a 0.1 pF tuner dielectric that lets me dial into the International Amateur Radio bands with pixel‑perfect resolution. Its 24‑bit, 14‑MHz ADC means that a weak voice transmission can sit beneath a strong local beacon and still pop up on the screen. The 1.5 GHz LNA brings the HF+ to the forefront of sensitivity, enabling me to hear Olivia even when her 20‑meter activity is in the background of a full‑band DX chain.
Exploring 80‑Meter to 10‑Meter with Real‑Time Demodulation
The trick was to let the Airspy’s square‑wave reference anchor the spectrum, so I set the sampling rate to 12 MHz and whittled it down to the station’s narrow slice. When the 80‑meter beacon flashed a clear signal at 3.54 MHz, the HF+ flashed it in blue, exactly as the QRP home /beacon mode would reveal. I switched now and then to the 40‑meter band, flashing 7.20 MHz and 7.28 MHz, and eventually, for a silver lining, hit the 20‑meter 14.26 MHz, where occasional Olivia repeats the tone.
The Real Pulse of the OLIVIA Signals
Since early 2024, Olivia expanded her repertoire to include a short‑wave packet transmission on 10‑meter, a clear 2.80 MHz beacon. The packet format, a compressed OSI layer, reveals a clear burst every 12 minutes, leftmost at 2790 kHz. The Airspy HF+, when paired with the new Olivia Enigma firmware, can demodulate the packet with a 0.5 dB margin over the normal 15 dB receiver noise floor.
Spectrograms, Plugins, and The Quiet Hunt
One week ago, the Airspy community rolled out version 2.35 which adds a plugin capable of real‑time FFT smoothing. With this, I can now watch the 21.23 MHz window 10 carrier ticks fluidly and isolate the “BIO” bursts that Olivia uses for feedback. I spent the night running Fldigi on top of ReaQHSDR, feeding it the demodulated audio from the HF+. The steady chiming of Olivia across 21.23 MHz was not only audible, but also visible through the spectrogram as a column of alternating white and dark stripes. Watching it, I felt a direct line to the station that once transmitted a joke according to the old 1980s scatter forums.
Future Horizons and New Frequencies
In the last month, a new amateur satellite named Ultramar FedEx launched at 437.778 MHz. Olivia switched her focus to tracking the satellite’s 437.678 MHz downward link, and the Airspy HF+ has kept pace by auto‑counting the Doppler shift of the burst to within 50 kHz. From 437.5 MHz to 438.0 MHz, I’ve observed a density of digital controllers that keep the drift of
The First Sweep on a Quiet Night
It was one of those evenings where the electric hum of the laboratory was almost invisible, except for the faint chirps of distant radios. I settled into my chair with the Airspy HF+, its USB dongle glinting in the dim lamp light, and prepared to listen to the amateur radio spectrum. The Airspy HF+ is a true workhorse: a 5 kHz–30 MHz tuner with a dynamic range that lets me chase weak signals without drowning in noise.
Preparing the Setup for MT63
MT63 is a digital voice mode that thrives on the HF bands; communities on 15 m, 20 m, and even 10 m use it to transmit clear voice across long distances. To find those signals I opened the SdrPlay app, selected the HF+ and set the bandwidth to 20 kHz, which gives enough excess for the 25 kHz MT63 frames while keeping the image clutter low. I then tuned to 21.250 MHz, the center of the 15 m amateur band, where MT63 is a common traffic carrier.
Listening to the Frequency Cadence
The radio landscape is a tapestry of continuous waves, narrow sweeps, and bursty digis. At 21.250 MHz I heard a rhythmic packet of symbols; the Airspy HF+ captured the subtle sidebands that MT63 modulation relies on. I noted that MT63 typically occupies a bandwidth of about 10.5 kHz, so my 20 kHz window was comfortably wide. The next band was 14.200 MHz on 20 m; there I listened to the familiar differential carrier signals moving in and out of range.
Decoding and Validation
To turn those oscillations into intelligible words I ran QSIREC with the MT63 plugin enabled. The software matched the Airspy’s captured spectrum, stepped through each symbol interval, and reconstructed the voice stream. When the audio playback kicked in, I could hear a well‑enunciated operator’s greeting, confirming that my tuning and filtering choices were right.
Finding the Perfect Spot in the 10 m Band
Next I moved to 28.150 MHz, the middle of the 10 m amateur band. Although MT63 is less common there, pockets of activity still exist, especially in the interior corner of New Zealand or during summer solar maxima. The HF+ handled the high‑frequency end just as well, and my 20 kHz window captured the narrow packet bursts that are hallmark of MT63 transmissions in this band.
Practical Tips for Anyone Else Trying the Same
Use a low‑noise wideband antenna such as a long wire or an inverted feedline; the HF+ is most powerful when the antenna presents a clean signal. Set the amplifier to low gain during initial scans to avoid saturating the ADC, then step up just enough for weak remote transmissions. Finally, keep an eye on the Noise Floor – the HF+ displays it accurately, and I found that setting a threshold of –110 dBm in QSIREC filters out the bulk of ambient hiss, letting the clean MT63 packets rise above the noise.
Closing the Night’s Listening
When I powered down the Airspy HF+, the last echo that lingered was the soft resonance from a distant 20 m station, its MT63 tokens fading into the ether. The drums of the circuits settled, but the memory of those digital voices remained. For anyone with a curious mind and a ready HF+ SDR those quiet frequencies are waiting to be decoded, one MT63 packet at a time.
Start of the story
The Quiet Shack
In a quiet corner of the county line, there’s a little shack that hums with the promise of the unseen airwaves. The walls, whitewashed and weathered, hold the Airspy HF+ – a tiny, unassuming fan‑cane that can sweep the entire 0.02 to 26.5 MHz spectrum. The ham operator, a seasoned explorer of the electromagnetic sea, turns the dial on a day that feels like a quiet prelude to a grand symphony.
First Light on the 3 kHz Band
The HF+ sits idle, listening to the whisper of the wind and the distant chatter of meteorological radios. Then, as sunrise breaks, the operator tunes the receiver to the lower short‑wave, a frequency that is often excluded by most when discussing PSK operations. In undisturbed 3 kHz bandwidth, the pilot geocodes a glorious PSK63 signal. The signal starts exactly at 3,000 Hz, hugging the band edge and fading softly into the 3,050 Hz mark. The 63‑symbol‑per‑second modulation shivers with a clean 120‑Hz bandwidth – a tight packet of data that the HF+ streams to the screen in real time.
Pushing the Envelope to 1.3 kHz
Not satisfied with a single breath, our ham finds a second vessel: a PSK125 mode on the 1.2 kHz band. The frequency lies cleanly between 1,200 and 1,330 Hz – a narrow slice often overlooked. The operative dives into the formoon (the portion of a falsetto frequency that keeps the resolution sharp) and hears the 125‑symbol‑per‑second cascade. Thanks to the HF+’s 0.02‑MHz lower limit, it can capture the faintest pulse, the pristine 140‑Hz wide envelope, and plot the digipeated packet onto a digital rose diagram.
Why the HF+ Makes a Difference
The Airspy HF+ isn’t just a receiver; it’s a bridge between careful manual tuning and software‑directed adventure. On the 3 kHz band, the Airspy’s extra 3 MHz tuner allows for real‑time spectrogram generation. That means a ham can spot a PSK63 or PSK125 channel with a single click, identify its exact frequency, and even measure its bandwidth, all while the device zooms in from 1.3 kHz to 4 kHz on a hot‑wired platter.
Implementing PSK63 and PSK125 Modes
On the software side, the ham uses a single‑band receiver UI that ingests the HF+ raw stream. By adding the
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