The first process is general noise levels reduction. Since the signal normally is not centered at the expected frequency, even Doppler-corrected, a setting must be present that re-centers the frequency and modifies the parameters of all filters to match the new characteristics of the signal. In the bellow flow graph we have following blocks: Low Pass Filter block that represents a low pass filter for signal adjustment. The next three blocks in the diagram below are used to analyze the signal shape and form logical levels. The block decoding the telemetry gives information created by the protocol AX.25 frame structure described above. Sink File module enables real time data storage on a local storage environment or in a space shared on the network that has access to the workstation. Writing is done in binary format (as standard float 32), and saved data can be processed further either GNU Radio using a block read (File Source) or in other programming environments. The whole diagram is shown in Fig. 9. Figure 9. Implementation of created digital signal processing block 5.CONCLUSION SDR provides a new approach to designing a network of ground stations satellite, an approach that brings primarily significant reduction in design complexity and cost and offers a flexible environment, versatile radio architecture development. Digital processing modules created (AX.25 decoder) in the development environment GNU Radio, offers a range of possibilities because the encapsulation and decoding blocks based on adaptive communication protocol AX.25 are used by other microsatellites. Also these modules would find implementing in a network of earth stations for more effective communication with microsatellites. On receipt of telemetry, configuring orbital data of any satellite and taking into account the position of the earth station may be omitted Doppler effect. It applies for any satellite.
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