Green Bank, WV


July 21,  2000
TO: R. Fisher, J. Ford, F. Ghigo, R. Lacasse,  C. Niday, T. Weadon
FROM: R. Lacasse
SUBJ.: Minutes of Interference Protection Group 07-21-00 Meeting

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

Minutes of Previous Meeting

Manpower Problems
At best, finding people to work on IPG matters has been a difficult challenge lately.  One engineer, Steve White, may have some time in available in the near future, but a technician will be harder to find.

Since funding is more or less constant in the short term, some re-ordering of priorities will be necessary to free up peoples' time to work on IPG projects.  The performance of the GBT and other site telescopes may be in serious jeopardy at frequencies below 2 GHz due to locally generated interference.  The group feels that this is a significant problem, deserving a reasonable fraction of the Green Bank engineering and technician effort.  Fisher and Ford will draft a memo which requests additional support and lists IPG related projects, and discuss it with McKinnon.

Site-wide Interference Suppression Policy
Ford stated that there is a need for a site-wide interference suppression policy.  The main problem is "people wanting to put computers everywhere."  Observations on 85-3 by Anish have demonstrated that the quality of the data can be improved by turning off various pieces of equipment.  There is insufficient data, however, to allow the identification of the worst offenders.

There are some positive developments in the area of mitigation.  For instance, the computer division intends to move critical servers to a shielded room, and some GBT systems have received a lot of interference-suppression attention.  However, the general attitude toward minimizing locally generated interference is mostly indifference.  Some ways to heighten awareness might include some type of formal statement from the IPG, design reviews of locally designed equipment taking RFI into consideration, testing of commercially purchased equipment, and committee approval of new site facilities.  It was also pointed out that equipment not in use could be turned off.

Ghigo pointed out that the 85-3 telescope can be used occasionally to monitor the local interference environment.  Fisher stated that the monitor station could improve on the 85-3 system by providing  broader frequency coverage and ascertaining the direction of the interference.

Science Education Center Design
The architect for the new Science Education Center is not very well schooled on RFI mitigation techniques.   He will require some input from the NRAO staff.  A memo should be written specifying the allowable emissions from the Center, and the likely shielding and filtering specifications required to achieve this.  Ford is now checking on the cost of materials to shield the 4000 sq. ft. exhibition area.

It was the general feeling of the group that the tour center budget should cover the cost of properly shielding the exhibit room, whether that entails paying for NRAO staff time or consultants.  This was driven mainly by the lack of available manpower to work on existing IPG projects.

A few approaches to shielding the area were discussed.  It was mentioned that the VLBA antenna control rooms were built with shielding specified, and later tested, by NRAO.  The general sentiment of the group was that something a bit stronger that this is required, although testing to a strict specification may be going too far.  Ford agreed to locate some documentation on the VLBA buildings.

Low Frequency Use of 85-3
Don Backer has notified us that he would like to continue using 85-3 and possibly expand its frequency coverage to include a band at 200  or 800 MHz.  He is currently seeking funding for this.  Again this highlights the need for the monitor station, and coverage from 200 Mhz to 1700 MHz.
Progress on Monitor Station
A summer student is making good progress on controlling rotators for the monitor station antennas.  Help is still needed packaging amplifiers and getting signals over fiber to the backends.  Rick will produce a block diagram of what is required in hopes of manpower becoming available.
RFI Testing
The new video conferencing system should be tested in the anechoic chamber.  Some of Heatherly's students identified it as the worst offender in the building.  This system should probably be turned off when not it use.

Also the shielded cabinet for a microwave oven for the operators is complete and should be tested.

Summary of Action Items
1 - Draft a position paper requesting support for the IPG from McKinnon and Jewell
2 - List IPG projects
3 - Specify shielding requirements for and estimate cost of shielding and filtering for the new Science Education Center, both manpower and materials.
4 - Dig up the VLBA memo about the shielding of the control buildings.
5 - Draw a block diagram detailing amplifiers and fiber modems so that a detailed design can be started.
6 - Add  the shielded cabinet for the operators' microwave oven, and the video conferencing system to the list of items that need to be tested  in the anechoic chamber.
Next Meeting:  August 22, 2000