Airspy HF+ Discovery vs RTL-SDR V4: HF Reception
RTL-SDR Blog V4 ($35) covers HF via a built-in upconverter; Airspy HF+ Discovery ($169) uses a dedicated HF front end and an 18-bit ADC. The HF+ Discovery hears weak signals the V4 misses by 15-20 dB.
Head-to-Head Comparison
| Category | Winner | Why |
|---|---|---|
| HF sensitivity (MDS / weak-signal performance) | Airspy HF+ Discovery | Airspy HF+ Discovery has -141 dBm typical MDS with an 18-bit ADC. RTL-SDR Blog V4 has roughly -120 dBm MDS with an 8-bit ADC after the upconverter losses. In WSPR / FT8 side-by-side tests on the same antenna, HF+ Discovery routinely shows 15-20 dB better SNR on weak signals — translating to copying stations the V4 can't decode at all. |
| Dynamic range | Airspy HF+ Discovery | HF+ Discovery's 18-bit ADC delivers ~95-100 dB usable dynamic range. RTL-SDR's 8-bit ADC delivers ~70-75 dB. On crowded HF bands with strong shortwave broadcasters, the V4's front end overloads and the entire spectrum gets crushed. The HF+ Discovery handles strong-signal environments without breaking a sweat. |
| Image rejection | Airspy HF+ Discovery | HF+ Discovery uses a polyphase harmonic-rejection mixer that mathematically cancels image responses at the silicon level. RTL-SDR's upconverter architecture creates phantom signals at sum and difference frequencies — strong local AM broadcasters often show as ghost signals on amateur HF bands. |
| Frequency stability (TCXO) | Airspy HF+ Discovery | Both have TCXOs rated ±0.5 PPM. HF+ Discovery additionally accepts an external 10 MHz reference input for GPS-disciplined operation — critical for WSPR / FT8 networks running 24/7 reference-locked. The V4 cannot accept an external reference. |
| Frequency coverage | RTL-SDR Blog V4 | V4 covers 500 kHz to 1.75 GHz continuously. HF+ Discovery covers 9 kHz to 31 MHz (HF) PLUS 60 to 260 MHz (VHF) but NOTHING between 31 and 60 MHz, NOTHING from 260 MHz to 1 GHz, and NOTHING above 260 MHz. For ADS-B, trunked radio, P25, UHF amateur, or 1.2 GHz amateur, V4 is the only option of the two. |
| Price | RTL-SDR Blog V4 | RTL-SDR Blog V4 is $35; Airspy HF+ Discovery is $169. Roughly 5x price difference. For most new SDR users the V4 is the right starting point; HF+ Discovery is the upgrade you buy when HF performance becomes the limiting factor in what you can hear. |
Which Board for Your Project?
| Use Case | Recommended | Why |
|---|---|---|
| First SDR for general learning | RTL-SDR Blog V4 | V4 covers ADS-B, NOAA weather satellites, broadcast FM, trunked radio, and HF reception via built-in upconverter — all at $35. HF+ Discovery's HF-VHF-only coverage is too narrow for a first SDR exploring multiple use cases. |
| Weak-signal HF DXing (CW, SSB) | Airspy HF+ Discovery | The 18-bit ADC + polyphase mixer hears signals at the noise floor that V4 loses entirely. For a serious HF DXer chasing rare DXpeditions on 20m / 40m / 80m, the performance difference is dramatic — measurable in dB and audible in copy. |
| FT8 / WSPR 24/7 spotting | Airspy HF+ Discovery | TCXO stability + clean reception means significantly higher decode rates. The HF+ Discovery's external 10 MHz reference input also allows GPS-disciplined operation for the most demanding spotters. V4 works but at a measurable disadvantage. |
| ADS-B aircraft tracking | RTL-SDR Blog V4 | ADS-B is on 1090 MHz — well above the HF+ Discovery's 260 MHz ceiling. Use the V4 for ADS-B; the HF+ Discovery literally cannot tune to that frequency. |
| Shortwave broadcast listening | Airspy HF+ Discovery | Broadcast SW (3-30 MHz) is the HF+ Discovery's home turf. The dynamic range advantage matters when listening to weak DX broadcasters that share the band with strong local stations. V4 will work but with audible noise and intermod from stronger signals. |
| Trunked radio / P25 monitoring | RTL-SDR Blog V4 | Trunked systems operate in the 470-870 MHz range — well above HF+ Discovery's coverage. V4 is the right tool; for serious trunked work add a second V4 (for control + voice channels) and run OP25 or SDRTrunk. |
Where to Buy
Final Verdict
Buy the RTL-SDR Blog V4 first. It's the right answer for almost everyone — 95% of new SDR users will find the V4 covers everything they want to do, including casual HF listening. Add the Airspy HF+ Discovery later, specifically when HF reception becomes the bottleneck in your hobby — weak-signal DXing, FT8 / WSPR spotting, or serious shortwave broadcast DX. The HF+ Discovery's strengths are wasted on ADS-B (above its range) or general scanner use (no UHF), so it's a complement to the V4, not a replacement.
Frequently Asked Questions
Does the Airspy HF+ Discovery cover UHF?
No. HF+ Discovery covers 9 kHz to 31 MHz (HF) and 60 to 260 MHz (VHF). It does NOT cover 31-60 MHz, 260 MHz to 1 GHz, or anything above 1 GHz. For ADS-B (1090 MHz), trunked radio (470-870 MHz), or amateur UHF (440 MHz), use the RTL-SDR Blog V4.
How much better is the HF+ Discovery on weak HF signals?
Typically 15-20 dB better SNR on the same antenna at the same QTH. Translated: signals that show as faint smudges on the V4 waterfall are clearly readable on the HF+ Discovery. WSPR decode rates on HF bands run roughly 2-3x higher with the HF+ Discovery vs the V4 in side-by-side tests.
Can I use both at once?
Yes. Different USB devices with different serial numbers. Common dual-SDR setups: HF+ Discovery on a quiet HF antenna for shortwave / amateur HF DXing, V4 on a discone antenna for VHF / UHF scanning. SDR# and SDR++ both support multiple SDR sources.
Does the HF+ Discovery support SpyServer for remote operation?
Yes. SpyServer (free from Airspy) runs on Windows / Linux / Raspberry Pi and serves the SDR over the network. Most serious HF DX setups colocate the HF+ Discovery + Raspberry Pi at a rural quiet site and connect from home via SpyServer over residential internet.
Is the HF+ Discovery worth 5x the price for casual listening?
No. For casual broadcast monitoring, occasional ham listening, ADS-B, and learning SDR fundamentals, the V4 is the right buy and the HF+ Discovery is overspend. The HF+ Discovery is justified when you specifically need the weak-signal HF performance for DXing, contesting, or 24/7 WSPR / FT8 spotting.
Can either transmit?
No. Both are receive-only. For TX-capable SDRs see the HackRF One (1 MHz to 6 GHz, half-duplex, ~1 mW) or PlutoSDR (70 MHz to 6 GHz, full-duplex, ~7 dBm). For HF TX specifically, use a real HF transceiver (Icom IC-7300, Yaesu FT-991A).