Please use this identifier to cite or link to this item:
|Scopus||Web of Science®||Altmetric|
|Title:||Adapting a cryogenic sapphire oscillator for very long baseline interferometry|
|Citation:||Publications of the Astronomical Society of the Pacific, 2011; 123(903):582-595|
|Publisher:||University of Chicago Press|
|Sheperd Doeleman, Tao Mai, Alan E. E. Rogers, John G. Hartnett, Michael E. Tobar and Nitin Nand|
|Abstract:||Extension of very long baseline interferometry (VLBI) to observing wavelengths shorter than 1.3 mm provides exceptional angular resolution (∼20 μas) and access to new spectral regimes for the study of astrophysical phenomena. To maintain phase coherence across a global VLBI array at these wavelengths requires that ultrastable frequency references be used for the heterodyne receivers at all participating telescopes. Hydrogen masers have traditionally been used as VLBI references, but atmospheric turbulence typically limits (sub)millimeter VLBI coherence times to ∼1–30 s. Cryogenic sapphire oscillators (CSOs) have better stability than hydrogen masers on these timescales and are potential alternatives to masers as VLBI references. Here, we describe the design, implementation, and tests of a system to produce a 10 MHz VLBI frequency standard from the microwave (11.2 GHz) output of a CSO. To improve long-term stability of the new reference, the CSO was locked to the timing signal from the Global Positioning System satellites and corrected for the oscillator aging. The long-term performance of the CSO was measured by comparison against a hydrogen maser in the same laboratory. The superb short-term performance, along with the improved long-term performance achieved by conditioning, makes the CSO a suitable reference for VLBI at wavelengths less than 1.3 mm.|
|Rights:||© 2011. The Astronomical Society of the Pacific|
|Appears in Collections:||Aurora harvest 2|
Files in This Item:
There are no files associated with this item.
Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.