Green Bank, WV


May 16, 2001
TO: R. Fisher, J. Ford, F. Ghigo, R. Lacasse,  C. Niday, T. Weadon
FROM: R. Lacasse
SUBJ.: Minutes of Interference Protection Group 05-15-01 Meeting

In attendance: Fisher,  Ford,  Lacasse, Niday, Ghigo

Minutes of Previous Meeting

Interference Reports
Review of Action Items:

   1. Interference Manager position status (John)

Two applications have been received.  In an effort to gather a larger pool of applicants, adds have been placed in IEEE Spectrum and EE Times.
  2. RFI considerations for new Education Center (John, Frank)
NRAO continues to test possible electronic gadgets for the building.   NRAO has committed to build shielded and filtered enclosures for several control systems to be used in the new building.  The computer lab and exhibition hall will be shielded, and the rest of the building will not.  A few weeks ago, the shielding consultant came to Green Bank; this resulted in some fruitful discussions.  Drawings for the building are due 5/14/01 (yesterday!).
   3. Site-wide interference suppression policy - position  paper (John, Rick)
Phil has read it.  No comments yet.
   4. Recent RFI experience with the GBT   (all)
Lacasse reported on efforts to shield and filter the magnetostrictive length transducers found in the servo system.  Using filtered DB-9 connectors and copious copper tape, emissions from the system were attenuated at least 65 db.  Unfortunately, this is nowhere near the required 124 db calculated by Niday, but should be sufficient to make a significant dent in the problem.  DB-9 filtered connectors are used because they are a convenient package containing multiple filters and they allow for a continuation of the shield.  Better connectors have been ordered because the ones used leaked quite a bit.  Also a test enclosure has been designed and submitted to the shop.  It will simulate the mechanical environment on the telescope better that the enclosure (copper tape) used for the above-referenced tests.  Also, a 40-ft. length of  cable identical to that used on the telescope has been obtained from Lockheed-Martin, and will be used in the next round of testing.

A new printed circuit for the CRAM mixers has been designed with RFI mitigation in mind.  Surface-mount ferrites were used successfully on the prototype, and were designed in to this board.

  5. Progress on suppressing RFI from equipment that has been measured in the anechoic chamber
Folded in to above.
   6. Monitor station developments (Rick)
White and Shank continue to make good progress with the RFI monitor station instrumentation.  The rotator controller electronics have been installed in an RFI-tight enclosure and will be tested in the anechoic chamber within the next few days.  Most of the RF and fiber electronics are ready to install or have already been installed in the weather-tight box at the station.  The weather-tight box may not be so weather-tight any more so a small roof to protect it from direct rain will be built over the box in the next couple of weeks.
   7. Measurements of PC/Workstation in a shielded box (Chuck)
The box is presently being used for the tests described in (4) above.
 Next Meeting:  June 19, 2001