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Synthesizers Eliminate Degradation From Phase Hits Careful design techniques in this 1-to-23-GHz synthesizer eliminate the cause of phase hits that can degrade high-speed telecommunication system performance.
Phase hits are infrequent but damaging causes of signal degradation in high-performance telecommunications systems, and their effect increases with data rate. As a result, the continuing increase in data rates dictated by dramatic increases in network traffic are making phase hits a prime target for elimination. Phase hits often have their origin in frequency sources, and the DFS Series from Elcom Technologies (Rockleigh, NJ) has been designed to reduce or eliminate phase hits arising from the signal source, while reducing susceptibility to microphonics to an extremely low level, and retaining low phase noise. The synthesizers are designed to meet the needs of high-capacity digital radios, MMDS and LMDS systems, Sonet and SDH optical networks, and satellite communciations applications Phase hits can be defined as sudden, uncontrolled changes in the phase of a transmitted signal that occurs randomly, and generally lasts for fractions of a second. It can be caused by temperature changes from dissimilar metals expanding and contracting at different rates, as well as from vibration or impact. In addition, detecting and measuring phase hits generally requires test equipment either designed for the purpose or modified to meet the stringent demands of not only measuring but also characterizing transitory events that last a few tens of microseconds at most. In addition, there has been no standardized measurement protocol on which to rely when evaluating a particular product. While phase hits (along with gain hits and assorted other degrading phenomena) have plagued communications equipment for years, today's higher transmission speeds accentuate the problem because of the greater amounts of data affected in a given time period. In developing a series of synthesizers that have as one of their primary attributes a total absence of phase hits, Elcom Technologies created its own proprietary phase-hit test system by which its products could be evaluated. The DFS Series is available for operation in frequency bands from 500 MHz to 23 GHz, with a tuning bandwidth of 1 GHz. Standard step sizes are 25, 125, and 500 kHz, and 1 and 10 MHz; switching speed is less than 25 ms. Phase noise is well controlled, with typical performance of -120 dBc at a 100-kHz offset from the carrier at X-band. The synthesizers were designed to provide significant resistance to microphonics, which can be a problem for equipment mounted in locations where it experiences wide temperature variations, as well as wind, rain, and hail that cause high levels of shock and vibration. Microphonics, which are acoustic vibrations that traverse an oscillator package and circuits and cause changes in phase and frequency, are dealt with in the DFS Series through a combination of materials, mounting, and enclosure techniques, as well as through careful circuit design. Elcom offers the DFS Series in various configurations based on customer requirements, including various frequency bands, step sizes, and output powers.
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