Green Bank, WV

MEMORANDUM February 23, 1999

TO: R. Fisher, J. Ford, F. Ghigo, R. Lacasse, R. Norrod, M. McKinnon, C. Niday, T. Weadon

FROM: R. Lacasse

SUBJ.: Minutes of Interference Protection Group 02/23/99 Meeting

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

Minutes of Previous Meeting


Call Outs for Interference

Some interference at 1293 MHZ was observed during a VLBI run on Feb 23. Plots were presented to the group by Lacasse and Ghigo. (The source of the interference was later identified to be an FAA radar in the Roanoke area that was grand-fathered in to the Quiet Zone.)

Action Item Review

1 - Technical Seminar on RFI Suppression Requirements and Techniques

Fisher presented an outline for a seminar on this topic and requested comments. Comments included:

- Make clear which bands are routinely tested,

- Need more time to review,

- Divide the seminar into two, one-hour, presentations,

- Consider giving pointers on printed circuit design techniques for minimizing interference,

- Discuss the GBT receiver room in more detail,

- Fisher to present the first half,

- Tag team approach on second half,

- Video tape the talks and make view graphs available,

- Include lists of vendors who manufacture filtering and shielding materials in the seminar,

- Designate site experts in filtering and shielding.

2 -Harmful Levels Document

Needs more work

3 - Use of Spectral Processor with anechoic chamber

Rick will probably work on this next week.

4 - Lab RFI Suppression Techniques

The Green Bank business manager, Mike Holstine, is sympathetic to the idea of trying to tackle internal RFI problems. Fisher proposed that one room be designated for a test case. Although the PBX room is tempting, getting cooperation from the telephone company might be difficult. The LAN room in the old part of the lab may be a realistic target. There was some discussion as to whether shielding rooms or racks would be the best approach. It was pointed out that PC's and workstations are not rack mounted. Postscript printers may also be a significant source of interference due to their heavy use of microprocessors. This led to a decision to bump up the priority of testing the PC enclosure. A decision was also reached to come up with an engineering design for fixing up a room, and to request funds from Phil Jewell, the site director, for this purpose. Several books in the library and in various offices may be helpful in this regard.

5 - Site Radio System

No change.

6 - Monitor station and anechoic chamber developments

No progress on monitor station.

Engineering design was completed on filters for the continuum detected power system. Detailed electrical and packaging design are presently underway.

7 - Microwave Oven Enclosure

A commercial enclosure was purchased ($1500) from EMCOR. Although it does not meet TEMPEST requirements, it is specified to provide up to 40 DB of shielding at 1 GHZ. Modifications to the enclosure will be made to improve the shielding and make it suitable for an oven enclosure.

8 - Shielded Room Entrances

The short-term goal is to prototype a serpentine entrance. Microwave-absorbing foam for a prototype was not located in the interferometer barn. There is some absorbing foam in the warehouse, but it may not be suitable for a prototype.

9 - Use of Interference Reporting System

The system is not being used. A review for the operators is probably in order. Fisher stated that starting the program is quite simple: just type "rfi" at a Unix prompt.

10 - Tourists Digital Cameras

No progress.

11 - Interference at 1612.17 MHZ

No progress.

12 - GBT Subreflector-Actuator Heaters

Testing is underway.

13 - RFI Considerations for new Education Center

Nothing new to report.

14 - RFI Monitor for Education Center

Tests in the anechoic chamber may lead to a system suitable for use in the Education Center

15 - Cal and Sig/Ref Switching System for Anechoic Chamber

No progress.

16 - FCC Class B requirements and test procedures

No progress.

Next Meeting: March 9 , 1999, at 0800