2,514 research outputs found
Dick effect in a pulsed atomic clock using Coherent Population Trapping
The Dick effect can be a limitation of the achievable frequency stability of
a passive atomic frequency standard when the ancillary frequency source is only
periodically sampled. Here we analyze the Dick effect for a pulsed vapor cell
clock using coherent population trapping (CPT). Due to its specific
interrogation process without atomic preparation nor detection outside of the
Ramsey pulses, it exhibits an original shape of the sensitivity function to
phase noise of the oscillator. Numerical calculations using a three-level atom
model are successfully compared with measurements; an approximate formula of
the sensitivity function is given as an easy-to-use tool. A comparison of our
CPT clock sensitivity to phase noise with a clock of the same duty cycle using
a two-level system reveals a higher sensitivity in the CPT case. The influence
of a free-evolution time variation and of a detection duration lengthening on
this sensitivity is studied. Finally this study permitted to choose an adapted
quartz oscillator and allowed an improvement of the clock fractional frequency
stability at the level of 3.2x10-13 at 1
Direct Digital Frequency Synthesizer Architecture for Wireless Communication in 90 NM CMOS Technology
Software radio is one promising field that can meet the demands for low cost, low power, and high speed electronic devices for wireless communication. At the heart of software radio is a programmable oscillator called a Direct Digital Synthesizer (DDS). DDS has the capabilities of rapid frequency hopping by digital software control while operating at very high frequencies and having sub-hertz resolution. Nevertheless, the digital-to-analog converter (DAC) and the read-only-memory (ROM) look-up table, building blocks of the DDS, prevent the DDS to be used in wireless communication because they introduce errors and noises to the DDS and their performances deteriorate at high speed. The DAC and ROM are replaced in this thesis by analog active filters that convert the square wave output of the phase accumulator directly into a sine wave. The proposed architecture operates with a reference clock of 9.09 GHz and can be fully-integrated in 90 nm CMOS technology
The advanced receiver 2: Telemetry test results in CTA 21
Telemetry tests with the Advanced Receiver II (ARX II) in Compatibility Test Area 21 are described. The ARX II was operated in parallel with a Block-III Receiver/baseband processor assembly combination (BLK-III/BPA) and a Block III Receiver/subcarrier demodulation assembly/symbol synchronization assembly combination (BLK-III/SDA/SSA). The telemetry simulator assembly provided the test signal for all three configurations, and the symbol signal to noise ratio as well as the symbol error rates were measured and compared. Furthermore, bit error rates were also measured by the system performance test computer for all three systems. Results indicate that the ARX-II telemetry performance is comparable and sometimes superior to the BLK-III/BPA and BLK-III/SDA/SSA combinations
Chapter Development of Josephson voltage standards
Neurology & clinical neurophysiolog
Development of Josephson voltage standards
Neurology & clinical neurophysiolog
Index to nasa tech briefs, issue number 2
Annotated bibliography on technological innovations in NASA space program
High resolution angular sensor
Specifications for the pointing stabilization system of the large space telescope were used in an investigation of the feasibility of reducing ring laser gyro output quantization to the sub-arc-second level by the use of phase locked loops and associated electronics. Systems analysis procedures are discussed and a multioscillator laser gyro model is presented along with data on the oscillator noise. It is shown that a second order closed loop can meet the measurement noise requirements when the loop gain and time constant of the loop filter are appropriately chosen. The preliminary electrical design is discussed from the standpoint of circuit tradeoff considerations. Analog, digital, and hybrid designs are given and their applicability to the high resolution sensor is examined. the electrical design choice of a system configuration is detailed. The design and operation of the various modules is considered and system block diagrams are included. Phase 1 and 2 test results using the multioscillator laser gyro are included
Wide-bandwidth high-resolution search for extraterrestrial intelligence
Research accomplished in the following areas is discussed: the antenna configuration; HEMT low-noise amplifiers; the downconverter; the Fast Fourier Transform Array; the backend array; and the backend and workstation
Cold atom Clocks and Applications
This paper describes advances in microwave frequency standards using
laser-cooled atoms at BNM-SYRTE. First, recent improvements of the Cs
and Rb atomic fountains are described. Thanks to the routine use of a
cryogenic sapphire oscillator as an ultra-stable local frequency reference, a
fountain frequency instability of where
is the measurement time in seconds is measured. The second advance is a
powerful method to control the frequency shift due to cold collisions. These
two advances lead to a frequency stability of at 7\times 10^{-16}^{87}^{133}$Cs fountains.
Finally we give an update on the cold atom space clock PHARAO developed in
collaboration with CNES. This clock is one of the main instruments of the
ACES/ESA mission which is scheduled to fly on board the International Space
Station in 2008, enabling a new generation of relativity tests.Comment: 30 pages, 11 figure
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