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Interference

Foley reported that WSRT had been involved in the recent Glonass experiment. The interference at 1612 MHz produced by the satellites severely effected VLBI observations. Spencer reported that Jodrell also participated in the experiment and that 1612 interference was also present at Jodrell but only when one of the satellites passed through the primary beam. Graham noted that the Lovell telescope had very good side-lobe levels and that may explain why the effect is more severe at other sites. Ruf reported that Glonass interference was present at Effelsberg. Garrett reported that at Jodrell the worst problem was centred at 1671 MHz and above. A band of around 12MHz centered on 1675MHz was completely unusable. Burgess believed that this interference was due to a local communications network. At Medicina nearly all the standard frequencies suffered from interference including 21cm. At Noto 18cm was mainly effected. Schilizzi enquired if there were not some way of bringing this to the attention of the authorities in Italy. The Noto and Medicina friends explained that the main problem was due to TV repeater stations and that in Italy there was a free-for-all which was uncontrollable. Junor reported that thorough interference monitoring at the VLBA had not yet been tackled. Foley suggested that we might consider switching 18cm to 21cm. This had the added bonus that more WSRT antennas would be available. Porcas noted that before switching we ought to consider who we might hurt. For example, monitoring programs. Schilizzi felt that a note about 18 cm interference should be made in the ``Call for Proposals''. Foley noted that at 610MHz the VLBA stations had a different frequency set up than the EVN. Schilizzi suggested that the VLBA standardize on the existing network standard. Burgess suspected that this was what they had already done.

ACTION ITEM: P. Burgess to establish the correct 50 cm frequency standard.

Burgess asked Schilizzi to summarize the Grenoble conference. Schilizzi reported that the scientific contributions were very interesting. However, there was still some work to be done before mm-VLBI was open to the Astronomical community at large. Junor thought that observations in the mm field would be adhoc for some time to come. Porcas asked what was the position of the Nobeyama telescope. Schilizzi felt that although most of the research was targeted to single-dish high frequency work they were more amenable to the VLBI technique than many others.

Bregman summarized his findings on the amount of spares available within the EVN. There was around 50,000 dollars worth of spares, most of which resided at MPIfR. Onsala could depend on Haystack for spares with an arrival time of 3 days! The situation was less rosy for other stations. Porcas suggested that every EVN station should have a spare set of heads at the very least. Bregman also noted that the heads should be replaced before they wear out. Porcas noted that there was a long lead time between ordering and actually receiving new heads. Schilizzi asked if it would be sensible to order 3 or 4 together and for them to be held centrally under optimum conditions. Burgess felt that it would probably not. Bregman asked the group for their opinion on local repairs. The feeling was that these were more time effective than cost effective.

Drawing the meeting to a close Burgess proposed that the group meet again around the first week in September (1993) probably in Torun, Poland.



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jive@nfra.nl
Fri Dec 17 08:20:53 MET 1993