Airspy HF+ Discovery
The Airspy HF+ Discovery is a premium receive-only SDR specialized for HF (9 kHz to 31 MHz) and VHF (60 to 260 MHz) reception, with an 18-bit ADC, ±0.5 PPM TCXO, and -141 dBm typical sensitivity. The MSi001 polyphase harmonic-rejection mixer plus LPC4370 DSP delivers performance the 8-bit RTL-SDR cannot approach on weak HF signals.
The right SDR for serious HF DXing and FT8/WSPR work — overkill for ADS-B or trunked-radio listening.
Where to Buy
Pros
- Polyphase harmonic-rejection mixer kills the image and harmonic spurs that plague cheaper HF SDRs
- 18-bit ADC oversampled to 16-bit IQ delivers dramatically better dynamic range than 8-bit RTL-SDRs in strong-signal environments
- ±0.5 PPM TCXO with external clock-disciplining input enables WSPR / FT8 work to within Hz across hours
- Separate HF (9 kHz to 31 MHz) and VHF (60 to 260 MHz) antenna inputs avoid front-end overload from co-located AM/FM broadcasts
- USB-C with aluminum enclosure — small enough for portable QRP setups, robust enough for permanent home installations
Cons
- Receive-only — no TX, even for digital modes (use a separate transceiver like an Icom IC-7300 for TX)
- 660 kHz alias-free bandwidth is narrow vs. wideband SDRs — fine for single-band monitoring, frustrating for spectrum-wide spotting
- $169 price point — three to four times an RTL-SDR Blog V4, even though both cover overlapping VHF range
Why 18-bit ADC matters on HF
HF (3-30 MHz) is a hostile band electrically — strong shortwave broadcasters, AM stations, time signals, and atmospheric noise all hit the antenna simultaneously. The receiver has to dig out a weak CW or FT8 signal from a sea of much stronger ones. The metric that determines whether the receiver can do this is dynamic range — the ratio between the strongest signal it can handle without distortion and the weakest signal it can detect above its own noise floor.
An 8-bit ADC (RTL-SDR) gives you roughly 48 dB of theoretical SNR per sample. After processing gain you can squeeze maybe 70-75 dB of usable dynamic range. The HF+ Discovery's 18-bit ADC delivers 95-100 dB of usable dynamic range. In practice that means the RTL-SDR's front end is desensed by a single strong AM broadcast station — the entire HF spectrum gets crushed when 10m above the noise floor. The HF+ Discovery handles the same RF environment without breaking a sweat. This is why serious HF operators (DX contests, WSPR farms, SWL DX hunters) standardize on Airspy HF+ Discovery or KiwiSDR.
Polyphase harmonic-rejection mixer and image suppression
The MSi001 chip used in the HF+ Discovery is a polyphase harmonic-rejection mixer — a quadrature mixer architecture that mathematically cancels image responses and odd-order harmonic mixing products at the silicon level. The practical result: when you tune to 14.074 MHz (FT8 on 20m), you don't get a phantom signal from 28.148 MHz leaking through as an image. Conventional superhet receivers need expensive multi-pole filtering to achieve image rejection; the polyphase mixer does it inherently.
Why this matters: HF amateur and shortwave broadcast bands are densely populated. A receiver that doesn't suppress images shows phantom signals at sum and difference frequencies from every strong broadcaster in your area. On an RTL-SDR with a basic input filter, the 40m amateur band (7 MHz) often shows ghost signals from local AM broadcasters at 750-900 kHz mixing with the local oscillator. The HF+ Discovery's polyphase mixer eliminates these — what you see on the waterfall is real signals at their real frequencies, not phantoms.
Software, antennas, and the WSPR / FT8 setup
On the software side, the HF+ Discovery runs in SDR# (the original Airspy-developed software), SDR++, GQRX, HDSDR, and SDR Console v3. SDR# with the SpyServer plugin enables remote operation — put the SDR at a quiet rural QTH with a good antenna, run SpyServer on a Raspberry Pi 5 there, and connect from your home laptop over the internet. This is how most remote DX operators run their HF+ Discoveries — colocated with a good antenna far from urban RFI.
Antenna matters more than receiver above 30 MHz. A long-wire HF antenna (20-40 meters), a magnetic-loop antenna, or a tuned dipole at 30+ feet will outperform any receiver indoors with a 1-meter whip. For FT8 / WSPR work, set up WSJT-X with the SDR's IQ output (via Virtual Audio Cable on Windows or pulseaudio loopback on Linux), tune to the band's FT8 frequency (7.074, 14.074, 21.074 MHz), and watch decodes appear. The HF+ Discovery's frequency stability means you can leave the rig decoding for 24+ hours without drift errors.
Full Specifications
Connectivity
| Specification | Value |
|---|---|
| rx_frequency_range | 9 kHz – 31 MHz (HF) + 60 – 260 MHz (VHF) [1] |
| max_sample_rate | 912 kSPS IQ (660 kHz alias-free bandwidth) [1] |
| tx_capability | Receive-only [1] |
| adc_bits | 18-bit (oversampled to 16-bit IQ) [1] |
| mds | -141 dBm typical (HF), -141 dBm typical (VHF) [1] |
| ip3 | +15 dBm typical [1] |
| reference_clock | ±0.5 PPM TCXO with disciplining input [1] |
I/O & Interfaces
| Specification | Value |
|---|---|
| antenna_connector | 2 x SMA female (HF + VHF) [1] |
| USB | USB-C [1] |
Physical
| Specification | Value |
|---|---|
| Dimensions | 76 x 45 x 12 mm [1] |
| weight_g | 50 g [1] |
| Form Factor | Aluminum enclosure [1] |
Who Should Buy This
The 18-bit ADC and polyphase mixer make weak HF signals readable that get lost in the noise on an RTL-SDR Blog V4. The MDS of -141 dBm typical translates to hearing CW signals at the noise floor on a quiet antenna. WSPR reports from the HF+ Discovery routinely show 15-20 dB better SNR than RTL-SDR setups on the same antenna at the same QTH.
The HF+ Discovery's strengths are wasted on ADS-B (works above 1 GHz, where this SDR doesn't reach), broadcast FM (overkill), and trunked radio (above 260 MHz, out of range). Start with an RTL-SDR Blog V4 to learn the software and antenna basics, then add an HF+ Discovery later if HF performance becomes the bottleneck.
Better alternative: RTL-SDR Blog V4
The TCXO frequency stability is critical — FT8 and WSPR tones must stay within ±50 Hz over a 10-minute window. RTL-SDR drift causes decode failures; the HF+ Discovery is rock solid. Pair with WSJT-X and a permanent antenna and you'll spot stations 8000+ km away on 30m or 40m FT8 routinely.
Frequently Asked Questions
Airspy HF+ Discovery vs RTL-SDR Blog V4 for HF reception?
The HF+ Discovery is dramatically better on weak HF signals — 18-bit ADC vs 8-bit, dedicated HF front end vs an upconverter sharing the V/UHF chain, ±0.5 PPM TCXO vs ±2 PPM. Side-by-side comparisons typically show 15-20 dB better SNR on weak WSPR / FT8 signals. The cost: 4x the price and no coverage above 260 MHz.
Does it work with WSJT-X and FLDIGI for digital modes?
Yes. Use SDR# or SDR Console v3 to demodulate the SDR output to USB audio (via Virtual Audio Cable on Windows or pulseaudio loopback on Linux), then point WSJT-X / FLDIGI at that audio device. The Discovery's TCXO stability is critical for FT8 / FT4 / WSPR — far better decode rates than RTL-SDR setups.
Can I use it for VHF FM or aircraft monitoring?
Yes for VHF aircraft (118-137 MHz) and broadcast FM (88-108 MHz) — both fall in the 60-260 MHz VHF input. NOT for UHF aircraft, trunked radio, P25, DMR, or anything above 260 MHz. For those, use an RTL-SDR Blog V4. The HF+ Discovery's VHF performance is excellent but the band coverage is narrow.
What's the alias-free bandwidth?
660 kHz alias-free bandwidth at the maximum 912 kSPS IQ sample rate. Wide enough to display a full HF band segment (e.g., the entire 20m amateur band from 14.000 to 14.350 MHz). Narrow vs. wideband SDRs like the HackRF One (20 MHz) — but the HF+ Discovery trades bandwidth for dramatically better dynamic range per Hz.
Does it support SpyServer for remote operation?
Yes. SpyServer (free from Airspy) runs on Windows, Linux, or Raspberry Pi and serves the SDR output over the network. Common setup: HF+ Discovery + Raspberry Pi 5 at a quiet rural site with a good HF antenna, connected to home over residential internet via SpyServer. SDR# at home connects as if the SDR were local.
Is there a TX-capable equivalent?
Not from Airspy. The HF+ Discovery line is receive-only by design. For a TX-capable equivalent in the HF range, use a real ham transceiver (Icom IC-7300, Yaesu FT-991A) or a TX-capable SDR (HackRF One covers HF but with very low TX power; ANAN ham SDRs cover HF with 100W+ output but cost $1000+).