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NAIC/AO Newsletter, March 1997
After a month-long quarantine in a San Juan Customs office, the Canadian S2 recorder has finally reached its temporary home at Arecibo Observatory. As their contribution to space VLBI in general, and the Japanese VSOP in particular, the Institute of Space & Terrestrial Sciences (ISTS) in Toronto, Canada, are installing three S2 recorders at Deep Space Network (DSN) sites in Australia, Spain, and California, and loaning five more to "worthy" ground radio telescopes. Arecibo has been selected among these lucky few. Among the aims of the Canadians for the five x S2-recorder array are: (i) to be a stand-alone facility to carry out a large part of the VSOP survey program, (ii) to exploit orbit time otherwise unavailable to the mission, and (iii) to enable the participation of important telescopes that would not be otherwise available (such as Arecibo).
Appreciation of the great sensitivity offered by Arecibo was reflected in a rather high demand for the inclusion of Arecibo in VSOP observing proposals resulting from the Announcement of Opportunity for the first 17 months of the mission. For this time interval, 1000 X 6.6-hr VSOP orbits are assigned to general observing time (GOT) proposals, Arecibo being requested in proposals totaling 256 orbits. We have since learned that several other proposals that did not specifically name the antennas required in the participating ground array would also choose to include Arecibo. Proposals including Arecibo appear to have fared rather well in the VSOP refereeing process, some having been included amongst the VSOP Key Science Programs. Also, a proposed large weak-source Arecibo-VSOP AGN survey has received a Class-A grading with 40 VSOP orbits allocated to it. In addition, Arecibo can also participate in the VSOP survey project of strong AGNs at 5 GHz.
The S2-array aims at 24-48 hr observing per week for the duration of the mission. This will be divided between VSOP GOT and VSOP survey observations. However, this amount of time is not required from Arecibo, given its particular characteristics, i.e. limited declination and azimuth coverage, and lack of a 22-GHz capability. The NAIC Director has committed Arecibo to support VSOP during its first 17 months of operation with 4% of Arecibo's observing time, assuming that the equipment is available to enable this.
The S2 recorder uses 8 x VHS (VCR) tape transports, modified for high-density, high-data-rate applications, and handles two 16-MHz bandwidths channels. The Arecibo Electronics Department is building baseband converters and samplers to interface the telescope IF/LO system to the S2 recorder. The tapes from the S2 recorder will mostly be correlated on the 6-station S2 correlator at Penticton, Canada. In addition to the recorder, a hydrogen maser frequency standard is required for Arecibo to participate in space VLBI. For this, an H-maser (NR model NR16, originally built by APL) has been supplied on loan by the Frequency Standards Lab of the NASA Jet Propulsion Laboratory (see Newsletter No. ?).
With the VSOP antenna (or HALCA, as it is now called) in orbit, we are getting ready to join the project. Within a few hours of the S2's arrival at Arecibo, Bill Sisk had put the S2 recorder together and it is now waiting to be attached to the telescope. The L- and C-band receivers are in place in the Gregorian dome and the new optics appear to be working fine. All that is now needed is the ability to point the telescope and completion of the baseband converter/sampler unit to complete the signal path to the recorder. We hope to achieve this by May when we are scheduled to join in test observations with HALCA.
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