MEMORANDUM April 27, 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 04/27/99 Meeting

In attendance: Fisher, Ford, Lacasse, Niday

Minutes of Previous Meeting

Approved with the exception of a minor change requested by Fisher.

Call Outs for Interference

None.

Action Item Review

1 - Technical Seminar on RFI Suppression Requirements and Techniques

Fisher, Niday and Schiebel presented seminars in the past month on the "why's" and "how's" on interference suppression. Members of the IPG have heard little feedback from these.

2 - Progress on RFI Suppression from equipment that has been measured in the anechoic chamber

Fisher noted that now is probably the time to move from simply testing devices for RFI to fixing them. Niday reported that both Schiebel and Pedtke have been actively working on fixing RFI problems in devices they have designed. Ford noted that redesign of the IF system in the GBT receiver room will cure a lot of the previous problems with that system. Lacasse reported that the GBT servo contractor, PCD, has agreed to replace their noisy encoder-power-supply ( a switching supply) with a linear one, on the basis of IPG testing. Several items have probably fallen by the wayside, however. Ford agreed to review the list of devices that need work and start pushing for that work to be done.

It was also mentioned that design reviews for any new designs may be a good way of catching possible RFI design errors. Ford agreed to try to push this.

One item that was not covered in the technical seminars is printed circuit board design techniques for minimizing RFI. One possible approach to disseminating this information is to compile a "cheat sheet" to be passed out to all engineers and technicians.

3 - Site Radio System

Progress recently has been limited to frequency searching. Installation and water tower tests are still TBD.

4 - Monitor station and anechoic chamber development

Construction and bench testing of continuum detected power system is complete. This system now needs to be tested in conjunction with data acquisition computer. This test should have a fairly high priority. To be useful, some type of general purpose box has to be used to turn power off and on to the device under test.

Pedtke and Wester are working on the monitor station as time allows.

5 - Microwave Oven Enclosure

A commercial enclosure was purchased ($1500) from EMCOR. It has recently been received and modifications to the enclosure are presently being made. The quality of the box was a bit disappointing, but it appears workable.

6 - Shielded Room Entrances

No progress. We need to purchase foam and no money is available.

7 - RFI Considerations for new Education Center

No progress.

8 - Use of Interference Reporting System

The system is not being used at the 140 ft. There is no point in pushing it until the GBT comes on line.

9 -Harmful Levels Document

No recent progress.

Budget

M & S money will be used to fund construction of the monitoring station until RE money becomes available, probably in July.

Next Meeting: TBD