Airspy HF+ Discovery SDR Rx
Airspy HF+ Discovery SDR Rx
As part of the so-called "Digitalpaket", the introduction of a new VAT system with far-reaching changes for cross-border online trade with consumers is being driven forward at EU level.
As of 01.07.2021, in B2C distance selling (transactions with end consumers), the previously applicable VAT delivery thresholds in the EU will be abolished and tax amounts will be owed directly in the country of delivery.
The so-called "distance selling regulation" will then apply.
From this point on, cross-border deliveries of goods to non-entrepreneurs will be taxable in the destination member state, and the corresponding amount of VAT will be payable there.
This means, for example, that as of 1.7.21, 20% VAT will be shown on invoices for deliveries to France, and 25% VAT will be shown on invoices for deliveries to Italy. The recipient in Italy therefore no longer benefits from the 19% VAT rate in Germany.
The manufacturer of the well-known SDR Airspy-R2, Airspy HF+ and the SDR Sharp software has further developed the HF+: the HF+ "Discovery" for shortwave and VHF.
The Airspy HF+ Discovery operates from 500 Hz to 31 MHz and from 60 to 260 MHz. Similar to the Airspy HF+ the "Discovery" also works as a "Zero-IF" SDR. The received signal is mixed directly into the AF range. This technology avoids many of the problems of classic receivers, but also presents the developer with new challenges. The Airspy HF+ Discovery meets these challenges by using three analog tuners. The tuner is preceded by fixed bandpass filters and continously tuned filters. As with the 'HF+', the mixers of the 'Discovery' are designed as harmonic rejection mixers and thus ensure exceptionally good linearity and spectral purity of the down-mixed signal. This is important for sensitivity, because the cleaner the signal, the less likely it is that a weak signal will sink into the noise. Very powerful AD converters are used for digitization. The following decimation steps (DDC) work with different methods to reduce (decimate) the data rate. The result is a very effective anti-aliasing filter that offers about 108 dBc reduction. The resulting signal has an 18 bit resolution, which is then scaled to 16 bit 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+ 'Discovery' 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 usually 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+ 'Discovery' 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.
The Airpy HF+ can be used with many different programs on different operating systems. SDR# is probably one of the most suitable, since it comes from the same developer.
GQRX (Linux, MacOS)
All programs which use an ExtIO.dll library can be used (HDSDR, Studio1, Elad FDM-SW2 and others).
Here is the source code for an ExtIO.dll library suitable for the Airspy HF+. The same web site also povides a compiled image, but which is probably not sufficiently tested. With wider proliferation of the Airspy HF+ SDR this DLL will become more stable, or other versions will become available.
Here is the source code for the libairspyhf at Github, an open source library for various platforms like Linux, MACOS etc.
Further information on Harmonic Rejection Mixers:
To better understand how a 'Harmonic Rejection Mixer' works, please see the following technical documents:https://www.ieee-jp.org/section/kansai/chapter/sscs/20111121/nauta.pdf