Frequency drift

About: Frequency drift is a research topic. Over the lifetime, 5054 publications have been published within this topic receiving 56191 citations. The topic is also known as: chirp rate.

A model for the frequency fine structure of auroral kilometric radiation

Abstract: A model for AKR frequency fine structure in which the fine structure is a natural consequence of the emission of electron cyclotron maser radiation in a nonuniform magnetic field is presented. The model is examined by using 1D electromagnetic particle-in-cell simulations. It is found that maser radiation is emitted as individual wave packets combine to form the drifting emission features that make up the fine structure. Rising frequency drifts are associated with wave packets emitted independently of one another. Wave packets that interact with one another produce features with falling frequency drift. The emission features produced have a large spread in both positive and negative frequency drift rates. The average positive drift rate of rapidly drifting features is found to be approximately proportional to the maser growth rate.

Automatic frequency control for digital tuning systems

Abstract: Apparatus is provided for automatically compensating for frequency drift in a digitally tuned varactor tuner. An Automatic Frequency Control signal for tuning the varactor tuner is produced in response to the direction of a tuning error. A signal level detector is used to inhibit the AFC signal when weak signals are being tuned by the varactor tuner thereby preventing continuous searching by the tuning system.

AC Polarization for Charge-Drift Elimination in Resonant Electrostatic MEMS and Oscillators

Abstract: This paper proposes the use of ac polarization for resonant electrostatic microelectromechanical systems that eliminates the frequency drift caused by dielectric charging and charge screening. It is mathematically and experimentally shown that an ac-polarized resonator can sustain stable oscillations when used in a positive feedback oscillator circuit. We also demonstrate an oscillator topology that generates a drift-free reference frequency tone with this technique in spite of using a resonator that exhibits large frequency drifts under dc polarization. Long-term data are presented for these drift-susceptible devices, showing a significant improvement in frequency stability.

Spectral-temporal evolution of low-frequency pulsations in the microwave radiation of solar flares

Abstract: Low-frequency pulsations of 22 and 37 GHz microwave radiation detected during solar flares are analyzed. Several microwave bursts observed at the Metsahovi Radio Observatory are studied with time resolutions of 100 and 50 ms. A fast Fourier transformation with a sliding window and the Wigner-Ville method are used to obtain frequency-time diagrams for the low-frequency pulsations, which are interpreted as natural oscillations of coronal magnetic loops; the dynamical spectra of the pulsations are synthesized for the first time. Three types of low-frequency fluctuations modulating the flare microwave radiation can be distinguished in the observations. First, there are fast and slow magneto-acoustic oscillations with periods of 0.5–0.8 s and 200–280 s, respectively. The fast magneto-acoustic oscillations appear as trains of narrow-band signals with durations of 100–200 s, a positive frequency drift dν/dt=0.25 MHz/min, and frequency splitting δν=0.01–0.05 Hz. Second, there are natural oscillations of the coronal magnetic loops as equivalent electrical circuits. These oscillations have periods of 0.5–10 s and positive or negative frequency drift rates dν/dt=8×10−3 Hz/min or dν/dt=−1.3×10−2 Hz/min, depending on the phase of the radio outburst. Third, there are modulations of the microwave radiation by short periodic pulses with a period of 20 s. The dynamical spectra of the low-frequency pulsations supply important information about the parameters of the magnetic loops: the ratio of the loop radius to its length r/L≈0.1, the plasma parameter β≈10−3, the ratio of the plasma densities outside and inside the loop ρe/ρi≈10−2, and the electrical current flowing along the loop I≈1012 A.

Device for correcting frequency shift due to the doppler effect in a transmission system

Abstract: The present invention relates to a device for correcting a frequency shift due to the Doppler effect in a transmission system. The device for correcting a frequency shift due to the Doppler effect is applicable to a transmission system in which a signal is transmitted in a transmission lobe between a transmitter and a receiver that are in relative motion. The frequency shift which is the difference between the frequency of the transmitted signal as measured at the receiver and as measured at the transmitter is presented as the sum of a center frequency characteristic of the transmission lobe plus a position frequency which is a function of the position of the receiver in the transmission lobe. The device includes means for tuning the receiver which has a tuning frequency such that said tuning frequency is equal to the sum of the transmitted frequency plus the center frequency.