Green Bank, WV

MEMORANDUM March 9, 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 03/09/99 Meeting

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

Minutes of Previous Meeting


Call Outs for Interference

None. Lockman searched for the source of a previous interfering signal at 1612.17 MHz. Just as he was about to start an azimuth scan, the signal disappeared. The signal appears to be locally generated, since it is very narrow-band.

Action Item Review

1 - Technical Seminar on RFI Suppression Requirements and Techniques

Ford to set up a date for the first seminar.

2 - Use of Spectral Processor with anechoic chamber

The interface to the spectrometer via the Exceed program was tested and works satisfactorily. The need to enter passwords was found to be annoying, but necessary.

3 - Site Radio System

Two antennas have been received.

4 - Monitor station and anechoic chamber development

The response of the fiber modems was measured. They are specified to operate between 100 and 1000 MHz. However, they had reasonable response from 20 to 2000 MHz. Their noise temperature was very high (almost 10 million degrees). Some IP3 measurements were made as well. There is 10 to 20 db of headroom for wideband noise signals. Fisher will write this all up.

Construction of filters for the continuum detected power system is in progress. Filters for the monitor station could be used with the continuum detector system, to limit noise input into the dectector.

5 - 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. Delivery is expected in about 6 weeks.

6 - Shielded Room Entrances

No progress.

7 -Harmful Levels Document

Will be handed out at seminar.

8 - Lab RFI Suppression Efforts

A the last meeting a goal was set to make significant imporvements in are of the lab. During this meeting, Fisher noted that before starting on this effort, the group needs to give some thought to ways of measuring the effectiveness of whatever we do. This is both a shielding and a filtering problem, so a simple measurement of power radiated from a transmitter in the room does not give the entire picture.

In conjunction with this project, several books have been ordered. Ford will notify people when they arrive, and Fisher will compile a bibliography to be included in the Harmful Levels document or on the IPG web page.

9 - Use of Interference Reporting System

No comments made.

10 - Tourists Digital Cameras

No comments made.

11 - Interference at 1612.17 MHZ

See "call-outs" above. Hopefully significant progress can be made when the monitoring station is completed.

12 - GBT Subreflector-Actuator Heaters and Feed Defroster

Testing of the effectiveness of the subreflector-actuator heaters is complete and must be analyzed. Turn-on transients from these heaters and the feed defroster are a concern. A means of remotely signaling these devices to power up and down may be necessary. There was some disagreement as to the best way to provide this signal, but general agreement that it is not a major problem, and that it should be used as a last resort, after all reasonable shielding and filtering methods have been exhausted. Recent tests indicate that the feed defroster may be operated continuously, and thus have no turn-on transients.

13 - RFI Considerations for new Education Center

The location of the new Education Center has been changed from near the run way to an unspecified location that will preserve the runway. This does not change the RFI concerns. Costs of filtering and shielding the building may have been seriously underestimated. However, the design is probably will not be altered until funds are available to commence work.

14 - RFI Monitor for Education Center

No progress.

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 23 , 1999, at 0800