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Fig. 1: Energy detection. one example: the R4000 from IZT, with its associated Signal Suite software. The R4000 is a digital receiver and signal collection system, and is designed to meet customer demands for dynamic range even in high-bandwidth applications. It supports multiple simultaneous users on multiple channels. As discussed earlier, bandwidth is a key factor in many applications. The R4000 provides an instantaneous bandwidth of 120 MHz, meaning it can handle GNSS data or other sources of wideband signals. This means that it can be used to replace multiple narrowband receivers, without compromising quality. It is worth pointing out that wideband receivers such as the R4000 use software-defined radio (SDR) capabilities to implement parts of the system. As a technology, SDR is capable of achieving the highest levels of RF quality, as long as it is combined with traditional high performance tuners before the analogue to digital conversion. Selective recording Of course, with such a wide bandwidth, there will be huge amounts of data generated. Any practical solution needs to be able to store and analyse this data, but one way to minimise the problem is to be selective in which segments of the signal are examined. With the R4000, all intercepted signals are stored in the first instance. Then, multiple operators or automatic classification and analysis tools can be used to browse through individual streams or multiple streams in parallel, no matter whether they were recorded in the past or are real time. This means that users can specify criteria to determine the signals of interest. For example, they could only look at signals where the incoming power exceeding a certain threshold. The determining factors can be independent of threshold, such as only taking eight fixed sub-bands within the 120 MHz bandwidth, and continuously monitoring these smaller frequency regions. In fact, the R4000 can extract up to 32 subbands, which may overlap. Automatic selection needs to happen quickly, with minimum latency. To achieve this, after digitisation, the R4000’s DSP section calculates fast, high-resolution power spectra (PSD) with configurable parameters and three different detectors (minimum, RMS and maximum) in parallel. This PSD data gives an overview of the activities in the frequency band, and can serve as a trigger source for selective capture – see figure 1. In the past, dynamically shifting the centre frequency of the region being captured would tend to cause data corruption, or for the signal to be dropped. The R4000 overcomes these problems, and allows arbitrary sections of the spectrum to be extracted, and the region of interest to be varied in real time without affecting signal integrity. The R4000 digitizes signals up to 140 MHz directly without additional frequency conversion, helping to improve dynamic range. For higher-frequency applications, the input frequency range can be extended to 3 GHz or 18 GHz, using the VUHF or SHF front ends. The R4000 includes highly-selective configurable signal preselectors to avoid signal overload problems, high-quality RF front-ends, and broadband digitizers – see figure 2. Software integration and storage Capturing the signal is just the start of the process – how can it be analysed and stored? In today’s systems, there is close integration between software and hardware to provide the most useful tools. For some applications, the complex postprocessing algorithms required are sometimes too slow to work in real time, so it is essential to store signals and process them offline. The R4000 storage system separates signal capture from post processing and analysis, providing minutes to days of buffering capacity, if required. The storage hardware used depends on the use case, with varying sizes possible of hard drives or solid-state storage. While new data from the sensors is being recorded, multiple users or post-processing modules can simultaneously access historic data in the storage system as well as live streams. The transition from live to recorded is completely seamless from the users‘ point of view. To handle the vast amount of data generated, an effective graphical user interface is needed. For example, the R4000’s software provides a customisable layout that can be switched from a basic overview to a fully detailed view. Customisable templates restrict the interface, helping users to focus on specific tasks. A Software Development Kit (SDK) and open data formats ensure easy interaction with third party software and system integration. This feature is commonly used to analyse signals with MATLAB®. Fig. 2: IZT R4000 overview. www.electronics-eetimes.com Electronic Engineering Times Europe December 2014 29


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