Date: Fri, 29 Nov 2002 15:19:11 +0300 From: Zinovy Malkin To: feissel@ensg.ign.fr, weh@gemini.gsfc.nasa.gov Cc: altamimi@ensg.ign.fr, markus.rothacher@bv.tum.de, oRSONI Alain Subject: Collocation of VLBI and DORIS Dear Colleagues, I would like to make a proposal which may be useful for collocation of DORIS and VLBI. As you know, the main problem is in radio frequency interference which can be (partially) solved in several ways (as discussed with DORIS people and Kristine Larson last year): - place DORIS beacon far from VLBI antenna (at least 2 km, e.g. Ny-Alesund), - place DORIS beacon well below horizon w.r.t. VLBI antenna, - have a natural shield between both antennas (e.g. a hill at Kokee), - stop DORIS beacon transmission during VLBI session (e.g. Yellowknife) Evidently, only the fourth is suitable for most VLBI sites, that lead to loss of DORIS data, which can be unacceptable if VLBI station is active enough and DORIS beacon is switched off during whole VLBI session. However, the amount of lost DORIS measurements can be substantially reduced, in my opinion, if DORIS transmission is inhibited only during VLBI scans when it is really harmful for VLBI. This can be made if VLBI Field System can provide some signal for DORIS beacon and the latter can receive this signal and stop transmission for time defined by Field System. I don't know if new generation of DORIS beacon has a possibility for external control. If not, maybe it is possible to implement such a feature. If you consider this idea as useful, it may help to solve the problem. Best regards, Zinovy ------------------------------------------------------------------------------ Dr. Zinovy M. Malkin e-mail: malkin@quasar.ipa.nw.ru Head Tel: +7-(812)-275-1024 Lab of Space Geodesy and Earth Rotation Fax: +7-(812)-275-1119 Institute of Applied Astronomy RAS http://zmalkin.com/ nab. Kutuzova, 10 http://www.ipa.nw.ru/PAGE/DEPFUND/GEO/zm/ St.Petersburg 191187 Russia ------------------------------------------------------------------------------