Comparison SDRplay RSPdx and RSPduo
Here’s a comparison of the SDRplay RSPdx vs RSPduo (and notes about the newer RSPdx-R2), aimed at how they differ for radio astronomy, HF/VLF/LF work, and general SDR use. If you like, I can also give a “which is better for your antenna setup” conclusion.
Summary comparison
| Feature | RSPdx | RSPduo |
| Number of tuners | Single tuner (one RF front end) (SDRplay) | Dual independent tuners (two front ends) (SDRplay) |
| Frequency coverage | 1 kHz → 2 GHz (continuous) (SDRplay) | Same: 1 kHz → 2 GHz (each tuner) (SDRplay) |
| Maximum instantaneous bandwidth | Up to 10 MHz (single tuner mode) (SDRplay) | In single-tuner mode, also up to 10 MHz; but in dual-tuner simultaneous mode each tuner is limited to ~2 MHz (SDRplay) |
| Antenna ports / inputs | Three software-selectable antenna ports: 2 × SMA (full range) + 1 BNC (to ~200 MHz) (SDRplay) | Three antenna input ports (for the combined device), with the usual arrangement of ports for both tuners (SDRplay) |
| Low frequency / HDR / dynamic range improvements | Has a special “HDR” (High Dynamic Range) mode below ~2 MHz to mitigate intermodulation, spurious responses, etc. (SDRplay) | While the RSPduo shares the same front end architecture, its main advantage is dual reception. The HDR / front-end dynamic range is similar (for each tuner) (SDRplay) |
| External clock / reference | Supports external 24 MHz reference input (MCX) for locking to GPSDO or shared clocks (SDRplay) | Also supports external clocking / reference, and can act in a clock-master/slave network of SDRs (SDRplay) |
| Use cases / unique advantages | Simpler (single tuner), full bandwidth, multiple antenna ports so you can switch antennas or input types. Also, being “single tuner” avoids complications of synchronising two channels. | Ability to monitor two different frequency bands simultaneously, or compare signals from two antennas, or use diversity/coherent techniques, or dual-band full duplex (e.g. HF + VHF). (SDRplay) |
| Limitations / caveats | Only one signal stream at a time (i.e. no true dual-band simultaneous RX) | In dual-tuner mode, bandwidth per tuner is limited (~2 MHz) (SDRplay) |
| Status / availability | The original RSPdx is no longer in full production; a revised RSPdx-R2 variant exists with improvements especially at low frequencies. (SDRplay) | Still available in current SDRplay product line (SDRplay) |
Notes on RSPdx-R2
Since the original RSPdx is being phased out, the RSPdx-R2 is probably more relevant to consider. The RSPdx-R2 incorporates enhancements particularly aimed at performance below ~2 MHz (noise floor improvements, better dynamic range in HDR mode, refined filters). (SDRplay) Otherwise its architecture (single tuner, 3 antenna ports, external clock) is similar to the original. (Moonraker Group)
For your purposes (antenna with two ends, single drop to computer), I lean toward the RSPdx-R2 over the older RSPdx.
What matters in your scenario
Given your configuration (two ends of an “antenna” held aloft, cable joining in the middle, single drop to computer), here are the practical considerations:
- If you only ever need one frequency band at a time, and you’re more concerned with maximizing sensitivity, dynamic range and simplicity, a single-tuner device like RSPdx (or RSPdx-R2) is simpler and avoids the complexity of coordinating two simultaneous tuners.
- But if you ever want to monitor two widely separate frequency bands at once (e.g., VLF and VHF simultaneously, or do diversity reception / coherence experiments), the RSPduo gives you that flexibility out-of-the-box.
- Because your antenna is a long wire/dipole-type, you’ll want very good front-end filtering and dynamic range, especially to avoid overload from strong signals (FM broadcast, local noise). The HDR modes and refined front-end in the RSPdx/R2 help in that regard.
- Also, synchronization is critical if doing coherent processing. With RSPduo both tuners are internally locked and share the same USB interface, so their timing is inherently aligned. Using two separate SDR units (or an external second tuner) often runs into issues of USB latency and timing skew. (SDRplay)
My verdict (for your use)
If I were in your shoes (antenna as you described, wanting flexibility but also reliability), I’d lean toward the RSPdx-R2 unless you have a strong need for simultaneous dual-band operation. The improvements in noise and dynamic range at low frequencies make it compelling.
However, if you foresee experiments that require simultaneous reception on two bands (or coherent combining) then the RSPduo is a strong choice.