Metsähovi Radio Observatory, Finland (vlbi@hut.fi) EVN Station Report, April 2004 Ari Mujunen (Ari.Mujunen@hut.fi) Jouko Ritakari (Jouko.Ritakari@hut.fi) Highlights During 2003 Metsähovi has continued the succesful series of disk-based 1Gbit/s and 2Gbit/s experiments using the VSI-based data acquisition terminals. A successful disk-based 1Gbps Metsähovi--Kashima experiment at 22 GHz was conducted in February 2003. This included both H2O maser and continuum sources, and it was correlated using CRL's high-speed software correlator. In March 2003 Metsähovi and Jodrell Bank observed at 22 GHz (as far as we know) the first international Mk4/Mk5A-compatible 1Gbps e-VLBI experiment. It was successfully correlated at JIVE with fringes detected on both H2O and continuum sources. Both Jodrell Bank and Metsähovi used MVDS to record Mk4 formatter data converted to VSI onto Linux hard disks. In June 17th 2003 Metsähovi and Kashima conducted the first international 2Gbit/s VLBI experiment. Data was recorded from the ADS-1000 sampler at 1Gsamples/s with 2-bit sampling. Like in the earlier Kashima-Metsahovi 1Gbit/s experiments, data was recorded in normal Linux files with PC-based disk recorders developed by CRL and Metsähovi, transferred via Internet with normal networking tools and correlated with a high-speed software correlator in Kashima. Fringes were found in both W3OH (water maser) and NRAO150 (continuum) data. For 1-bit correlation the SNR was 20.9 and for 2-bit correlation the SNR was 27.6, the SNR of 2-bit correlation was 32% larger than that of 1-bit correlation, as was expected. The 2Gbit/s experiment with Kashima was repeated in December 2003. Geodetic VLBI Project The neighbouring Geodetic Observatory's project to start geodetic VLBI observations at Metsähovi is slowly advancing. The S/X receiver built by TTI Norte, Santander, Spain, has arrived and due to its heavy (>115kg) construction, it needs mechanical fitting to antenna pedestal. It features standard geodetic RCP-only S and X bands. The system temperature of this receiver is around 80 K when the LNAs are cooled to 15 K and the bulky feed system and polarizers are at room temperature. The receiver has been installed in the radio telescope and a new, manually swappable subreflector has been manufactured and installed. First fringes were obtained in Nord01 geodetic test experiment 1st March 2004. The receiver seems to work well but two of the fourteen baseband converters ' were broken. Next Generation VLBI Project Since the termination of PCEVN project Metsähovi has continued the development of Metsähovi VSI Data System (MVDS). It is a simple and scalable multi-Gbps data acquisition system that adapts easily to the evolution of commodity PC technology. The VSIB data I/O PCI board has been complemented with Metsähovi Multi-Mode VSI Converter (MMM) which is based on universal VSI-H converter board, VSIC. These convert existing Mk4/VLBA formatter, VLBA sampler, and S2 DAS sampler signals into VSI-H for easy recording with any VSI-H-compatible recorder, including our VSIB board. The VSIB data I/O PCI board was tested in June 2002 by recording simultaneously data with both old recorder system and VSIB board system at Westerbork. The correlation of both data concluded identical fringes at JIVE. The board is VSI-H compatible and it supports bit stream assigments including all Mark5A 64/32/16/8 track formats. A total of one hundred of VSIB and VSIC boards has been manufactured in August 2002 and they are immediately available from Metsähovi. Several VSIB/VSIC systems have been delivered to stations in Australia, Germany, Italy, Japan, the Netherlands, the United Kingdom, USA and Canada, where the systems are being used for disk and e-VLBI, fringe checks, single-dish spectral and pulsar work. For pricing and for several documents on the subject, please see the Web address 'http://kurp-www.hut.fi/vlbi/instr/'. Using standard microcomputers and Linux has proven to be a very successful strategy. The performance of the system keeps improving when the computer industry developes faster computers. We expect the next big improvement to be the arrival of the new Nvidia Nforce3 250 GB motherboards that have native 1Gbit/s Ethernet and native serial ATA ports. Another interesting technology for VLBI is the Serial ATA port multiplier standard, which allows up to fifteen Serial ATA devices to be connected to one Serial ATA port. This greatly simplifies Serial ATA cabling and allows up to 30 hard disks (with today's 250GB disks that would equal 7.5TB or 12 thin tape capacity)to be connected to a standard microcomputer. Station Hardware/Software New H-Masers and Maser Room The temperature control system of our isolated maser "cave" has been revised multiple times by the local constructor. Currently it seems to succeed in keeping the temperature constant within +/-0.5C. The effectivity of humidity control is under current investigation. At this moment we use two Russian Kvarz H-masers, with Kvarz-69 as the station frequency reference and Kvarz-70 as backup and---if necessary---autotuning Kvarz-69 by using automatic frequency control. During the last year we have had two maser breakdowns, with Kvarz repairing the masers reasonably quickly. One of the breakdowns was caused by a thunderstorm, the other was repaired under warranty. Receivers The 22 GHz and 86 GHz receivers are functioning as before. The 43 GHz receiver is still being repaired for its broken RCP HEMT. A new pair of 43 GHz (LCP/RCP) HEMTs was purchased from the "YLINEN Electronics Ltd." in September. The HEMTs have already been installed but their required DC and bias arrangements are still due. Metsähovi has ordered a new dual-feed 80-115/150 GHz SIS receiver from Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS, Nizhny Novgorod). 80--115 GHz will be LCP/RCP while 150 GHz will be LCP only (using a 1/4-lambda plate to convert LCP to RX native polarization). The receiver was deliverd in May 2003, with integration efforts continuing thru 2003. The new receiver will replace the old 86 GHz RX. Recorder It has been known since 2001 that some high-numbered recorder tracks are producing marginal recordings. Investigations in the end of September did not reveal anything new, the headstack is probably 2/3 worn but should be still usable. As a result (and as a result of an earlier decision not to perform thin/thick tape switching anymore) we decided to increase the thin tape vacuum from 6in to 9in. In February 2003 EVN session this seemed to help somewhat, and probably more lapping with thin tape will further improve recording quality. The second head installation is still pending. It is most probable that MH will not invest to old technology, i.e. buy new head stacks. VLBI Sessions in 2003 Metsähovi participated in May-2003 and Feb-2004 22 GHz EVN sessions. Due to the limited staffing Metsähovi did not participate in any CMVA sessions in 2003. Manpower Prisse Könönen left the Metsähovi VLBI group in summer 2003.