The developer of the well known SDR Airspy-R2 has announced a new receiver, developed in cooperation with ITead Studio and a leading semiconductor manufacturer - the Airspy HF+.
The Airspy HF+ operates from 9 kHz to 31 MHz and from 60 to 260 MHz. The new design of the SDR receiver is based on a "Zero-IF" concept, whereby the received signal is mixed directly into the baseband range. This technology avoids many of the problems of classic receiver designs, but also presents developers with new challenges. The Airspy HF+ meets these challenges by using three analog tuners with fixed and tunable band filters. The mixers are designed as harmonic rejection mixers and thus ensure an extraordinarily good linearity and spectral purity of the down-mixed signal. This is important for a good sensitivity, because the cleaner the signal, the less likely it is that a weak signal will be lost in the noise. Two very capable AD-converters are used for digitizing the baseband signal. The subsequent decimation stages (DDC) work with different methods for reducing (decimating) the data rate. The result is a very effective anti-aliasing filter that provides approximately 108 dBc reduction. The resulting signal has a resolution of 18 bits, which is then scaled to 16 bits for transmission via the USB 2 interface.
Such a receiver design requires a very precise AGC to achieve the best possible sensitivity and high dynamic range. The software of the Airspy HF+ microcontroller controls the amplification in each stage of the tuner and the subsequent filters and amplifiers. The result is a dynamic range of theoretically 113 dB, practically 110 dB is achieved (on shortwave). This is an excellent result for such a compact receiver of this price range. The user benefits from the very good linearity and the high dynamic range as the received spectrum is much cleaner and free of artifacts. Manual gain control is not necessary, nor is the use of attenuators, preamplifiers, selective band filters etc.
In addition to the excellent RF characteristics, the developers have achieved an equally remarkable noise reduction at the AF level. Here, the disturbing noise in a desired signal is largely eliminated, without the signal suffering from intelligibility and without too many artifacts in the AF. The best way to hear the effect is to listen to the sample povided below.
Another highlight of the Airspy HF+ is the free software "SpyServer", which offers an easy to set up remote server. Here, a small computer (a cheap Raspberry PI or similar) can take over the function of the server to which the Airspy HF+ is connected. The receiver can then be accessed via the network in the usual way, even with several listeners at the same time. The difference to other web-based concepts is that the transferred data is actually an IQ signal, which can then be processed by the usual SDR software with all plug-ins. You are not hindered by the limitations of a web browser as SDR software.