The design of the National Radio Astronomy Observatory's Expanded Very Large Array (EVLA) project is approaching completion. Four of the twenty-seven antennas have been upgraded into the final configuration. The 2200 miles of fiber optic cables have been installed underground and are functional. The master oscillator and the round trip phase hardware have been operating uninterrupted since November 2003. Hundreds of hours of test observations have been performed as we start the task of characterizing the upgraded system. This paper discusses the results of this testing and describes the techniques used to maintain phase coherence of the EVLA LO chain and of the new wideband receivers. The enhancements to the VLA system include a new local oscillator (LO) system, a fiber optic LO distribution system, and a digital round trip phase measurement system. The phase requirement for the LO system requires that the long term phase drift slope be less than 6.0 picoseconds per 30 minutes at 40 GHz and be maintained across the entire array. To accomplish this, a near real time continuous measurement is made of the phase delay in the fiber optic cable distributing the LO reference signals to each antenna. This information is used by the correlator to set the phase on each of the baselines in the array.
The Expanded Very Large Array (EVLA) uses fiber optic technologies for intermediate frequency (IF) digital data transmission, and local oscillator and reference distribution (LO). These signals are sent on separate fibers to each of the 27 EVLA antennas. The data transmission system transmits the four digitized IF signals from the antennas to the central electronics building. A sustained data rate of 10.24 Gbits/s per channel and 122.88 Gbits formatted per antenna is achieved. Each IF signal uses a set of three channels, twelve channels in total, and is wavelength division multiplexed onto a single fiber. The IF system configuration includes an EML CW laser, an erbium doped fiber amplifier (EDFA), passive optical multiplexers, up to 22 km of standard single mode fiber, and an APD optical receiver.
The LO system uses two fibers to provide a round trip phase measurement at 1310 nm. The phase requirement for the LO system requires that a phase stability of less than 2.8 picoseconds per hour at 40 GHz be maintained across the entire array. To accomplish this, a near real-time continuous measurement is made of the phase delay of the amplitude modulated 512 MHz signals that are distributed to each antenna. This information is used by the correlator to set the delay on each of the baselines in the array. This paper presents a complete description of the two EVLA fiber systems, LO and IF, including specific component specifications.
The Expanded Very Large Array (ELVA) uses fiber optic technologies for the Digital Data Transmission, the Local Oscillator and Reference distribution, and all Monitor/Control functions. These signals are sent on separate fibers to each of the twenty-seven EVLA antennas. The Data Transmission System (DTS) is used to transmit the four digitized IF signals from the antennas to the Central Electronics Building. A sustained data rate of 10.24 Gbits/s per channel and 122.88 Gbits formatted per antenna is supported. Each IF signal uses a parallel interface of three synchronized single bit high-speed serial optical fiber transmission channels. Each set of three channels, twelve channels in total, is wavelength division multiplexed onto a single fiber. The formatted data are received and de-formatted before the data are sent to the correlator. The system configuration includes a CW laser, an Erbium Doped Fiber Amplifier, passive optical multiplexers, up to 22 km of standard single mode fiber and an APD optical receiver. This paper presents a complete description of the EVLA fiber system including specific component specifications. The calculated performance of the IF system is compared to the actual performance and resulting "Lesson Learned" are presented.
The goal of the Expanded Very Large Array (EVLA), project is to upgrade a world-class astronomical instrument in the meter-to-millimeter wavelength bands. The project combines modern technologies with the sound design of the existing Very Large Array (VLA) to increase by an order of magnitude the sensitivity, resolution, and frequency coverage of the existing instrument. This paper discusses the techniques used to maintain phase coherence of the EVLA system. The enhancements to the VLA system include improved feeds and receivers, new Local Oscillator (LO) and Intermediate Frequency (IF) systems, a fiber optic LO distribution system, high speed digitizers, 10Gbps digital links, a dense wavelength division multiplexed fiber transmission system, and a new high speed correlator. The phase requirement for the LO system requires that a phase stability of 2.8 picoseconds per hour at 40 GHz be maintained across the entire array. To accomplish this, a near real time continuous measurement will be made of the phase delay in the fiber optic cable distributing the LO reference signals to each antenna. This information will be used by the correlator to set the delay on each of the baselines in the array.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.