Subject: Collocation of VLBI and DORIS
From: Zinovy Malkin <[email-masked]>
To: [email-masked], [email-masked]
Cc: [email-masked], [email-masked], oRSONI Alain <[email-masked]>
Date: Fri, 29 Nov 2002 15:19:11 +0300

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
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Dr. Zinovy M. Malkin                          e-mail:  [email-masked]
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
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