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Very Low Frequency Receiver front end with high sensitivity and frequency selectivity


OBJECTIVE: Demonstrate new VLF receiver front end for NC3 airborne missions. The technology requires high sensitivity for distance reception of weak signals in the 14kHz to 60kHz range and high selectivity to discern a signal of interest from crowded VLF band. DESCRIPTION: Current airborne VLF receiver technology for Emergency Action Message (EAM) reception must meet stringent reception capabilities in harsh environments. Receivers were designed in the 1970s and 1980s to accomplish this task in certain environments, against certain threats. Since that time, USAF VLF transmitters have significantly decreased, providing a much weaker signal for VLF receivers to copy. Furthermore, the threat to Nuclear Command Control and Communication (NC3) has arguably become more adaptable and global, demanding that USAF EAM reception become more adaptable and global in response. Relying on Navy VLF Transmitters dispersed around the world could pick up the slack, but current USAF VLF receivers cannot tune to them. A new front end (that part of the VLF receiver between the antenna and demodulator) designed to copy both USAF and USN transmissions could address some of these problems, but this feature would add new problems of additional signals from transmitters occupying dense space in frequency. This topic targets a front end technology that would require high sensitivity to copy messages at distance and fine selectivity to tune to a specific transmitter whose frequency may be very close to that of another transmitter. In addition to these challenges, VLF receiver technology is expected to perform under the excessive noise of jamming sources and nuclear scintillated atmosphere (post Nuclear or high EM pulse event). Compounding these obstacles to robust VLF reception in currently fielded equipment are obsolete technology, poor logistics and sustainment management, strict funding lines, and a decimated VLF industry base and expertise. The VLF Receiver front end must surpass state-of-the-art receiver specs (see reference). A full VLF receiver design that meets these capabilities may lie outside of the duration and funding scope this research project and so the front end was chosen as a suitably scoped topic. The front end alone will not be enough to solve USAF survivable VLF reception issues, but a modular front end technology developed through SBIR could be integrated with other receiver subsystems in the future for full functionality. The research and demonstration of this front end technology is independent of the three other VLF topic submissions (Flight line VLF transmitter, militarized VLF antenna, hardened Human Machine Interface for VLF receiver). PHASE I: Develop an architecture for a VLF receiver front end with high sensitivity (<0.325uV) and selectivity (filter with>60dB out-of-band-rejection). Determine which components are COTS available, and which require further development. Identify critical components and perform RF compatibility modeling. The front end design must consider airborne NC3 mission requirements (Jammer & Noise rejection). PHASE II: Design, build and test VLF receiver front end and demonstrate performance in a simulated stressed channel (airborne, jamming, long distance, atmospheric scintillation). Develop packaging requirements and interface control document to ensure flight worthiness. PHASE III: Integrate VLF front end with operational VLF receive system for flight demonstration. REFERENCES: 1. Cohen, M.B.; Inan, U.S.; Paschal, E.W.;"Sensitive Broadband ELF/VLF Radio Reception With the AWESOME Instrument,"Geoscience and Remote Sensing, IEEE Transactions on, vol. 48, no.1, pp. 3-17, Jan. 2010. 2. Klein, M.;"Autonomous Ultra-Low Power ELF/VLF Receiver Systems,"Dissertation Stanford University, Nov. 2009. 3. Morton, T.; Sickles, K.;"The Role of Propagation Effects in Airborne RF Communication Systems Design,"Aerospace and Electronics Conference, 2008. NAECON 2008. IEEE National, pp.78-84, 16-18 July 2008. 4. THALES VLF/LF digital multichannel receiver (TRC-2556);
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