1,721,342 research outputs found
Time and Synchronization for OVRO LWA352
No full textThe two objectives of time tagging and synchronization usually have very different requirements for accuracy and precision. A fast signal is used to obtain the required accuracy, but with low ambiguity; a slower signal then has just enough accuracy to resolve the ambiguity of the fast signal, but larger ambiguity. We continue in this way with additional signals until the desired ambiguity is achieved, retaining the first signal's accuracy. The key is that each signal must resolve the ambiguity of its predecessor, and of course all signals must be consistent with each other (all derived from the same clock). This memo considers the time tagging of the 704 simultaneous OVRO-LWA samples received by the 11 FPGAs
ADC Crosstalk Measurements with SNAP for OVRO-LWA
No full textThe LWA (Long-Wavelength Array), located at Owens Valley Radio Observatory, is a powerful and sensitive radio telescope. OVRO-LWA needs very good signal transmission with minimal spurious emissions carried through its signal chain. The telescope receives analog radio signals from space, then interprets them as digital data that can be computationally analyzed to gain a better understanding of what that data means. In order to minimize unwanted effects, some parts of the signal chain are being redesigned. This includes possible changes in the ADCs employed, the FPGA used, or the circuitry linking the two. A variety of options are available for the new hardware, including several boards from the CASPER1 collaboration. Currently, the LWA uses CASPER ADC16x250-8 RJ45 rev 1 boards with HMCAD1511 ADC chips. A different CASPER board, or a new combination of ADC and FPGA hardware from multiple platforms, may be used. Among the candidate replacement boards is SNAP2 (Smart Network ADC Processor). In order to determine the viability of retooling the SNAP board for this purpose, the performance characteristics of its ADC hardware have been tested.Originally published at http://www.tauceti.caltech.edu/LWA/lwamemos.html
RFI Environment at the OVRO LWA: Quantitative Measurements
No full textMeasurements of the power spectral density of signals received by a few selected OVRO LWA antennas were collected for at least 24 hours over the frequency range 0 to 165 MHz. The objective was to quantify the RFI environment, concentrating primarily on the signals outside the target observing band of 25 to 85 MHz. Those out-of-band signals are subject to suppression by filtering. Significant filtering is practical only after the signals are delivered to the processing shelter, so these results can be used to set the dynamic range requirements for the RF-over-fiber links from outer antennas and for the pre-filtering analog signal processing at the shelter, as well as the amount of filtering needed to keep the signals within the dynamic range of the digitizers. It is found that the total power below 20 MHz (HF communication) is highly variable with peaks about 16 dB above the total power in the observing band, and that the total power above 88 MHz (primarily FM radio) is very stable at about 29 dB above the minimum power in the observing band. Sporadic in-band RFI is also seen.Originally published at http://www.tauceti.caltech.edu/LWA/lwamemos.html
Ohje varautumisesta rautatieonnettomuuksiin (OVRO)
Get PDFEi voimassa. Korvattu Liikenneviraston ohjeella LIVI/2821/07.02.00/2016 Ohje varautumisesta rautatieonnettomuuksiin (OVRO
A History of OVRO: Part II
Get PDFBefore the advent of big, national radio-telescope arrays, Caltech's Owens Valley Radio Observatory was a worldwide mecca for interferometry
OVRO CMB anisotropy measurement constraints on flat-Lambda and open CDM cosmogonies
No full textWe use Owens Valley Radio Observatory (OVRO) cosmic microwave background (CMB) anisotropy data to constrain cosmological parameters. We account for the OVRO beamwidth and calibration uncertainties, as well as the uncertainty induced by the removal of non-CMB foreground contamination. We consider open and spatially-flat-Λ cold dark matter cosmogonies, with nonrelativistic-mass density parameter Ω0 in the range 0.1–1, baryonic-mass density parameter ΩB in the range (0.005–0.029)h-2, and age of the universe t0 in the range (10–20) Gyr. Marginalizing over all parameters but Ω0, the OVRO data favors an open (spatially-flat-Λ) model with Ω0≃ 0.33 (0.1). At the 2σ confidence level model normalizations deduced from the OVRO data are mostly consistent with those deduced from the DMR, UCSB South Pole 1994, Python I-III, ARGO, MAX 4 and 5, White Dish, and SuZIE data sets
The OVRO blazar monitoring program
No full textThe OVRO 40 m Telescope monitoring program carries out twice-weekly measurements of the 15 GHz flux density of nearly 1600 blazars and other AGN, including all those associated with northern (declination > −20°) Fermi Large Area Telescope (LAT) detections and a preselected sample ideal for statistical studies. We present some results from the program and describe the statistical method we have developed to assess the intrinsic radio variability of the sources in our sample. We also present a method for assessing the significance of correlations between radio and gamma-ray light curves
Long-term OVRO monitoring of LS I +61º 303: confirmation of the two close periodicities
Get PDFContext. The gamma-ray binary LS I +61° 303 shows multiple periodicities. The timing analysis of 6.7 yr of GBI radio data and of 6 yr of Fermi-LAT GeV gamma-ray data both have found two close periodicities P_(1,GBI) = 26.49 ± 0.07 d, P_(2,GBI) = 26.92 ± 0.07 d and P_(1,γ) = 26.48 ± 0.08 d, P_(2,γ) = 26.99 ± 0.08 d.
Aims. The system LS I +61°303 is the object of several continuous monitoring programs at low and high energies. The frequency difference between ν_1 and ν_2 of only 0.0006 d^(-1) requires long-term monitoring because the frequency resolution in timing analysis is related to the inverse of the overall time interval. The Owens Valley Radio Observatory (OVRO) 40 m telescope has been monitoring the source at 15 GHz for five years and overlaps with Fermi-LAT monitoring. The aim of this work is to establish whether the two frequencies are also resolved in the OVRO monitoring.
Methods. We analysed OVRO data with the Lomb-Scargle method. We also updated the timing analysis of Fermi-LAT observations.
Results. The periodograms of OVRO data confirm the two periodicities and .
Conclusions. The three independent measurements of P_1 and P_2 with GBI, OVRO, and Fermi-LAT observations confirm that the periodicities are permanent features of the system LS I +61°303. The similar behaviours of the emission at high (GeV) and low (radio) energy when the compact object in LS I +61°303 is toward apastron suggest that the emission is caused by the same periodically (P_1) ejected population of electrons in a precessing (P_2) jet
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