Message 5/525 apolatid@oso.chalmers.se Oct 18, 2000 09:56:35 am +0200 X-Authentication-Warning: arvak.oso.chalmers.se: apolatid owned process doing -bs Date: Wed, 18 Oct 2000 09:56:35 +0200 (CEST) To: evntech@jb.man.ac.uk Subject: EVNtech: ONSALA TOG report Sender: owner-evntech@jb.man.ac.uk Precedence: bulk ONSALA SPACE OBSERVATORY TOG REPORT - Torun Oct 2000 REPORT ON THE LAST OBSERVING SESSION ------------------------------------ No major problems arose during Session 3/2000. A slight problem with low amplitude of the phase-cal unit in the 25m antenna was fixed during the 5cm spectral line experiments. NEW HARDWARE ------------ Immediately after Session 3/2000 the new dual polarization L-band feed was tested. This is a scaled version of the UHF feed, and will eliminate the need to change feeds between 21cm and 18cm. The effective bandpass is between 1200-1450 MHz and 1594-1720 MHz. Laboratory testing of the polarization purity showed 5% crosstalk at 18cm, which goes down to 1% at 21cm. The new feed was tested with the MITAC room temperature low noise amplifiers (which are used for the UHF observations) and its performance was according to specifications. The next step is the manufacture of waveguides to connect the feed to the cooled amplifiers and the construction of a new LO chassis to enable remote switching between 18cm and 21cm. Finally, by Session 1/2001 a new, lower noise amplifier will be installed in the RCP channel. It is hoped that during Session 4/2000 the feed will be ready to operate with the cooled receivers and only LO switching would have to be done manually. This will reduce the switch-over time to 30min from the 1.5 hrs that was necessary until now. Mark 4 RECORDER --------------- Recently we have noticed a signal interfering to the read head electronics, which was giving rise to high(er) parity errors, particularly in the even and higher number tracks. This signal apparently was coming from either the inchworm or the LVDT cables (with the LVDT being the more probable), which were passing very close to the amplifier boards of the read head. The cables were 'redirected' and the interference was reduced significantly (but not eliminated) so the parity errors now appear much lower. LOGISTICS PROBLEMS EXPERIENCED SINCE THE LAST TOG MEETING --------------------------------------------------------- During session 2/2000 we had, once more, problems with FEDEX returning to us a tape sent to the NRAO Correlator. This was a part of a three tape shipment, the other two tapes found their way to Socorro the first time round. This problem has happened a few times during the past couple of years, nobody at FedEx could explain why. PERSONEL CHANGES ---------------- None >From the Onsala VLBI team