Subject: Re: Collocation of VLBI and DORIS
From: "H.Fagard" <[email-masked]>
To: [email-masked]
Cc: [email-masked], Martine Feissel-Vernier <[email-masked]>, Frank Lemoine <[email-masked]>, "A. Orsoni" <[email-masked]>, [email-masked], Kazuo Shibuya <[email-masked]>, Bill Outhwaite <[email-masked]>, "Cox, Clyde A." <[email-masked]>
Date: Thu, 5 Dec 2002 15:31:37 +0100

Dear Colleagues,

At 18:39 +0300 4/12/02, Zinovy Malkin wrote:
>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):
>
>(...)
>- have a natural shield between both antennas (e.g. a hill at Kokee),

I have recently returned from Kokee where I have upgraded the DORIS 
equipment (new antenna on a more stable support, and 3rd generation 
beacon).
I also installed the first equipment at this site in 1990, and at 
that time there was a natural shield between the "old" 9 meter VLBI 
antenna (many trees and maybe the top of a hill, but it was difficult 
to say because of the trees).
When I was in Kokee two weeks ago I was surprised to see that there 
was direct visibility between the old DORIS antenna (and this will 
also the case for the new one) and the 20 meter VLBI antenna that 
replaced the 9 meter one. This has been so for quite a few years (I 
don't know when the 20 m antenna was installed) without the VLBI 
people ever reporting any interference to us. Maybe the reason is 
that the DORIS antenna is lower than the VLBI?

>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.

I'm Cc'ing our host agencies at Yellowknife (Bill Outhwaite) and 
Syowa (Kazuo Shibuya), who perform VLBI measurements and need to turn 
off DORIS when doing so, so that they can comment on DORIS being 
harmful for VLBI only during scans.

>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.

See Alain's reply: yes, the last generation beacon has such a feature.

Best regards,

Hervé
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Herve FAGARD                              e-mail : [email-masked]
Institut Geographique National
94165 SAINT-MANDE CEDEX                     PHONE : + 33 1 43 98 81 48
FRANCE                                        FAX : + 33 1 43 98 84 50
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