Broadly tunable microwave reference oscillator developed.The measurement of phase-modulation (PM) noise and amplitude-modulation (AM) noise of clocks and oscillators presumes the availability of stable, low-noise reference oscillators at the desired measurement frequencies. However, it is too expensive and cumbersome to maintain dedicated reference oscillators for each measurement frequency. NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. researchers have developed a novel reference-oscillator system with broad tunability, which advances the art of PM and AM noise measurement. Previously, methods for synthesizing offsets from stable, fixed-frequency oscillators had been extremely complex. The problem is that frequency-offset synthesis generally creates unacceptable levels of noise. In the traditional approach, a synthesized offset is added to a stabilized oscillator oscillator Mechanical or electronic device that produces a back-and-forth periodic motion. A pendulum is a simple mechanical oscillator that swings with a constant amplitude, requiring the addition of energy at each swing only to compensate for the energy lost because of air . The noises of these two signals are independent and additive. The innovation of the new system is in the placement of the offset synthesizer synthesizer Machine that electronically generates and modifies sounds, frequently with the use of a digital computer, for use in the composition of electronic music and in live performance. inside a servo An electromechanical device that uses feedback to provide precise starts and stops for such functions as the motors on a tape drive or the moving of an access arm on a disk. control loop used to stabilize a high-Q microwave cavity. The frequencies of the two oscillators, the reference signal and the offset, must add up to the fixed reference frequency of the cavity. Therefore, the reference-signal frequency will be changed in a direction opposite to changes in the synthesized offset frequency. The system suppresses the total noise on the reference signal. The concept was experimentally demonstrated using a high-Q microwave cavity with a resonance frequency of 10.6 GHz, a dielectric dielectric (dī'ĭlĕk`trĭk), material that does not conduct electricity readily, i.e., an insulator (see insulation). A good dielectric should also have other properties: It must resist breakdown under high voltages; it should not resonant oscillator, and a digital offset-frequency synthesizer. The results demonstrated the addition of tunability without substantially adding to the noise. CONTACT: David Howe
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