Review of Airspy HF+/R2

Recently, I was contacted in IRC by prog, the author of SDR# and developer of the Airspy hardware - I was offered two Airspy models for review.
I've also got an RTL-SDR, so, in my opinion, a comparison would be interesting too.

Unboxing (HF+)

Photos

Airspy HF+ in its box — The box my HF+ came in looks very nice.

The bottom of the HF+'s box — The bottom of the box.

HF+ inside its box — Inside the box is the unit itself, the SMA connectors for HF and VHF antennas are visible.

A card with a link to the official website — There's also a little card with a link to the Airspy website.

Holding an HF+ — The unit feels pretty heavy despite the relatively small size.

Unboxing the R2

Photos

Airspy R2 in an anti-static bag — The R2 came in an anti-static bag.

The connectors of the R2 — There is a microUSB connector and also an MCX for connecting an external clock signal source to improve the frequency precision.

In addition to both receivers, I've received a pair of high-quality USB cables with ferrite chokes.

Specifications

The models differ considerably since they're intended for different purposes.

Device	Frequency range	Sample rate
Airspy HF+	0.009 - 31, 60 - 260 MHz	768 kHz
Airspy R2	24 - 1700 MHz	Up to 10 MHz¹
RTL-SDR	24 - 1700 MHz²	Up to 2.5 MHz³

An unofficial firmware allows sampling up to 80 MHz (however, the USB interface doesn't have enough bandwidth to handle that in real-time).
Assuming the tuner is an R820T, also 0 - 14.4 MHz and 14.4 - 28.8 MHz aliased.
Up to 3.2 MHz, but with dropped samples.

As you can see, RTL-SDR and Airspy R2 work well for UHF reception, while the HF+ is focused on HF and VHF.

Comparison

A UHF monopole antenna — The UHF antenna used for the tests.

Signal	HF+	R2	RTL-SDR
FM, strong
FM, weak

It's clear that both HF+ and R2 perform much better than an RTL-SDR.

DVB-T signal — Due to the very high sample rate of the R2, wideband signals can be received too.

DVB-T signal, demodulated in Gnuradio — The signal above, decoded with Gnuradio

Tip: you can use the decimation setting of the R2 to trade bandwidth for SNR and dynamic range.

Shortwave reception

RTL-SDR and Airspy HF+ can receive the shortwave bands.

I was once again amazed at the sensitivity of the HF+ - it could receive a few stations with the terrible antenna you can see above, which is more suited to UHF reception.
The RTL-SDR could receive some signal too, albeit it was much weaker.

And when I went outside and attached a 10 - 15m long-wire antenna to the appropriate input (via a terminal block, a short piece of coaxial cable and an F-to-SMA adapter - there was no matching circuitry such as a balun at all!), the results were astonishing.

The medium-wave band, as received by Airspy HF+

Shortwave broadcast stations — Airspy HF+ receiving shortwave broadcast stations.

Ham radio, BPSK31 — Ham radio bands, BPSK31 decoding

And now, a comparison with RTL-SDR:

Signal	Airspy HF+	RTL-SDR¹
RTTY, 10100.8 kHz
WEFAX, 13882.5 kHz Note the strong AM station nearby.
MSK carrier, VLF, 29.7 kHz²

The RTL-SDR is in the direct sampling mode
Despite the spectrum looking like as if there's a signal present, the RTL-SDR only receives some interference.

The RTL-SDR is unsurprisingly deaf, since it's not intended for HF reception.

Issues

The only disadvantage if the Airspy units I noticed is that the R2 sometimes receives images of the GSM band on about 300 and 600 MHz.
prog suggested using a table of optimal gain settings, this does help greatly, however some interference is still present.

Conclusion

I think the Airspy receivers would definitely satisfy an advanced user who already has some experience working with SDR, to whom some cheaper solutions such as RTL-SDR don't offer enough performance and features anymore.

There's also dedicated software called SDR#, well-known among the SDR enthusiasts, but it only works under Windows, which I don't use due to my desire to stick with FOSS.

Credits: prog for the supplied hardware; Alexandru Csete, the author of gqrx, my favorite SDR program - its screenshots are displayed above.

Home