Figure 1.
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NAIC/AO Newsletter, March 1997
Construction work on the telescope is rapidly approaching completion with only two major tasks left--alignment of the elevation rails and completion of the alignment of the azimuth rails. The remedial work on the alignment of the dome elevation trolleys has been completed with verification of its success waiting on the alignment of the elevation rails. The contractor, COMSAT-RSI, anticipates that these major tasks will be finished by the end of April. The final tensioning of the cable system was completed in February. During this operation the suspended structure went from approximately 40 inches below its final design height for correct focussing to about 18 inches above it. It will be pulled down to the design height, and maintained there under temperature changes, and dome and azimuth motions, by computer-controlled jacks pulling on the three vertical tie-down cables attached to the apexes of the platform. Drift scans of a number of radio sources were obtained as the platform passed near the design height. Figure 1 shows the beam shape obtained for a source passing within about 0.5' of the beam center. The estimated sensitivity was 7.3 K/Jy at 1.4 GHz, about 70% of the design value. Given that the optics were only roughly in focus this is an encouraging number.
Figure 1.
April should also see the completion of the contract with Continental Electronics for the 1.0-MW S-band transmitter. In December the transmitter went through its acceptance tests on the telescope culminating in a 5-hr full-power test into the telescope's tertiary reflector. Despite some people's expectations and a few false alarms, neither the horn nor the tertiary reflector melted. Emissions and full load tests for the 2.5-MW turbine generator, which supplies the primary power for the transmitter, were successfully completed in February.
Completion of the structural work will mark the beginning of the commissioning of the telescope with initial emphasis on focussing the optics to check performance, commissioning the azimuth and elevation drive systems and achieving the ability to track a celestial object. Receiving systems are completed or very close to completion covering the frequency ranges 410-450 MHz, 1.0-1.7 GHz, and 4.0-5.8 GHz. The 8.0-10.0-GHz system and the refurbishment of the 2.38-GHz maser for the planetary radar system are close to completion. Radio frequency interference is a serious problem in several of these bands and considerable effort is going into both characterizing the interference and devising methods to minimize its effects. The new local oscillator/intermediate frequency system and the fiber optic links to the platform are being checked out, and the new autocorrelation spectrometer and radar decoder are being tested. While much has been done, a considerable effort is still needed to integrate all the systems to form a working telescope. This activity will occupy most of the NAIC staff for the next several months.
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