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
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
11 - Interference at 1612.17 MHZ
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
16 - FCC Class B requirements and test procedures
Next Meeting: March 9 , 1999, at 0800