NATIONAL RADIO ASTRONOMY OBSERVATORY Green Bank, WV MEMORANDUM June 10, 1997 TO: R. Fisher, R. Lacasse, R. Norrod, M. McKinnon, C. Niday, T. Weadon FROM: R. Lacasse SUBJ: Minutes of Interference Protection Group 6/27/97 Meeting In attendance: Fisher, Lacasse, Niday, and Weadon RF: Changes to minutes of previous meeting? RL: No. Progress on Action Items: - Interference reports: All: No call outs. CN: Sizemore advised me about a Navy test of the GPS system at about 1300MHz. Did not get any complaints because of it. Equipment Tests: CN: I have been working with Schiebel, testing the feed defroster. I have built a cable for testing the feed rotator and provided it to Bob Simon, who is discussing with Norrod just how to test the rotator. A summary of equipment tested to date follows (provided after the meeting and included here): Gregorian Feed Defroster - 2-4-97, 2-20-97, 2-21-97, 5-6-97, 5-21-97, 6-3-97 Laser Rangefinder & Control Panel - 5-15-97 (Roger wants me to help Dave Parker figure out how to fix problems). Sun Workstation "Rigel" and accessories - 3-24-97, 4-23-97 Gateway 2000 PC "Spica" and accessories - 4-16-97 Switching Signal Mux system - 2-21-97, 5-6-97 RX Room L.O. Rack - 5-7-97 RX Room I.F. Rack - 5-1-97 Turbo Vac Pump - 5-8-97 Single Board Control & Reset Units - 5-2-97 (quietest thing tested so far) Assorted Portable Radios (RX) - 5-7-97 (not on list) Assorted Portable Radios (TX) - 5-7-97 (not on list) Items remaining include: Video Cameras (not even purchased yet, so I've heard) Surface Actuators/Controllers Feed Rotator & Motor Rack (Test cable for getting data to/from unit in test chamber has been given to B. Simon to test.) Weather Electronics (still on the tower) Bauser Refrigerator/Controller (I have had trouble getting up with D. Williams on this, so I sent him an e-mail) Vac Ion Pump/Controller TW: The spectrum analyzer in use at the anechoic chamber was borrowed from the 140' for a month, and I believe we've had it longer than that. Can it be returned soon? CN: We have a demo unit that we can use for a while. RL: For impulsive transients, would it not be better to use a continuum receiver, such as the one in the indoor/outdoor test facility, and sync it to the DUT? RF: Yes. CN: Measurements of impulsive interference made so far were accomplished by widening the resolution bandwidth of the spectrum analyzer to 1MHz. RL: Tests of the feed arm servo are scheduled to re-start next week. We should be prepared to do some EMI measurements at that site then. TW: Items that need to be tested soon include the feed rotator, the Bauser refrigerator, and the Vac Ion Pump/Controller. **** Action item for Weadon: get the above items scheduled. - Indoor Range Instrumentation: TW: The fiber link from the anechoic chamber to the 140' is still not working. There is a possible fiber problem. Childers is the person working on this problem. **** Action item for Lacasse: check with Childers on the status of the fiber. CN: I have evaluated a demo unit from Advantest. A demo unit from IFR was lost in shipment by UPS; a replacement demo is on the way. Also another Advantest demo is on the way. Anritsu is also sending a demo. HP is a known quantity and one or more of their units will be evaluated after the evaluation of the others. RL: Does Tektronix make a spectrum analyzer? CN: They no longer do. They are affiliated with Advantest and Rhodes and Schwarz. RL: I have purchased and received two amplifiers to drive the fiber link. I believe it is best to wait on purchasing other items on the block diagram, presented at the last meeting, until we have purchased a spectrum analyzer. Then we will know how much money we've got. All: Agreed. Interference Potential from Interferometer Control Building RF: Part of the upgrade of the tourist program involves making the Interferometer Tour Building into a tourist attraction. Some sort of simulated control room would be set up there. Due to its proximity to the GBT, this project presents a significant interference potential. Is anyone coordinating with the planners on this matter? All: No. **** Action item for Fisher: Coordinate with Lockman on above. All: Other interference sources include the Timing Center in the Interferometer Control Building, the Laser Lab, the 140'. RL: It would be a huge and expensive task to make the site compliant with the standards we are setting for new equipment on the GBT. RF: Probably the best we can do in this regard is to handle the worst offenders. Tektronix EMI Course RL: It seems like a good course, but I have used my travel allocation for the year. Perhaps it would be worthwhile for Chuck to attend. CN: Also, there are several engineers who are not very well versed in EMI mitigation. All: Perhaps an in-house course consisting of a video-taped course and some lectures by IPG group members would be valuable. It would be best to wait until fall, when hopefully we have had some successes. All will keep an eye out for an appropriate set of video tapes. Synthesizer to be shared with SETI. TW: The SETI group requested that we share the cost of a synthesizer with them. They would be sending this unit to other sites on occasion. This is incompatible with GBT needs, and SETI has been thus informed. RF: The IPG group will not have enough money in the near term to by a general purpose synthesizer anyway. What we probably wind up with will be simple, inexpensive, special purpose units. Our high end frequency is 2 to 3 GHz. TW: The Wavetek synthesizer which is the spare for the Spectral Processor is available for IPG use. Shielded Workstations and PC's RL: Thanks to leads from John Dreher and Chuck Niday, I have located several companies which sell TEMPEST qualified workstations and PC's. Thus far I have studied information from one of these and requested prices on several units. RF: It would be useful to get prices to help in the decision of whether to shield the GBT control room, or buy shielded computers. RL: In the long run, it seems like a shielded control room would be easier, since it would only have to be done once. Buying TEMPEST shielded equipment, or equivalent, will be a perennial problem. TW: I have asked the shop to build an metal box to contain a workstation, to see how effective it would be. RL: I have received information on very fine mesh screen (approx 250 wires to the inch) which can be used to view terminals. I will pass this information along to you. This type of material could be supported by a metal frame and conductive epoxy. - Next meeting: at 0800 on the same date as the next coordination meeting.