NATIONAL RADIO ASTRONOMY OBSERVATORY Green Bank, WV MEMORANDUM June 24, 1997 TO: R. Fisher, R. Lacasse, R. Norrod, M. McKinnon, C. Niday, T. Weadon FROM: R. Lacasse SUBJ: Minutes of Interference Protection Group 6/24/97 Meeting In attendance: Fisher, Lacasse, McKinnon, and Niday RF: Changes to minutes of previous meeting? RL: I received a few changes by e-mail. These were incorporated and the minutes redistributed. Progress on Action Items: - Interference reports: All: No call outs. - Shielded workstations RL: I distributed a short note showing an estimated cost increase for using commercial TEMPEST qualified workstations in the GBT control room for 20 years. The increase in cost, about $450K, was a real eye-opener. The TEMPEST spec is classified secret. It's main goal is to prevent poaching of information from equipment, via radiated signals. This can be accomplished either by shielding or jamming the signals of interest. The manufacturers with whom I spoke chose to implement the spec by shielding and filtering. Interest in TEMPEST equipment has decreased in recent years due to the demise of the cold war. Due to the high cost of TEMPEST qualified equipment, there has been some talk of shielding equipment ourselves rather than buying commercial off the shelf equipment that does the same thing. Personally, I think this is a waste of man-power. ****Action item for Fisher: Discuss with Norrod where we go from here with regards to workstations and PC's. - Calibration of the link to the 140 ft. RL: With a lot of help from Niday and Childers, the IF and TTL links between the anechoic chamber and 140 ft. are working. If we are to use the links to determine shielding requirements, then some sort of calibration is required. What is required? Broadband noise source, one or more CW signals? RF: A broadband noise source is not difficult to make using amplifiers with a terminated input. There are also diode noise sources. RL: Can their spectral power density be measured with filters and a power meter? RF: Yes. RL: One concern I had was that an external calibration source would change the average power level going into the system significantly, possibly leading to some sort of error. RF: Generally the CAL signal need add only about 10% to the system temperature. RL: Could we consider switching between the antenna and a termination at the input to the pre-amp. This would keep the system noise level almost constant, since we are only using the link to the 140 ft. when the signal is undetectable with the spectrum analyzer? RF: This could be done if we know the gain and noise figures of the amplifiers in the chain. ****Action item: Lacasse and Niday to gather data for this type of switching system and go over calculations with Fisher. - EMI Testing of GBT Equipment CN: Have done additional testing on components of the feed defroster. The motor is now undetectable. Work is being done on other components of this system by Schiebel. More testing will be done later. Have concluded that measurements of the VAC ION pump made recently are invalid. These pumps are used only when a dewar has been evacuated and cooled. In my tests the dewar had not been cooled. I plan to do further testing on a cooled dewar. Other items on the list are on hold for reasons beyond the IPG group's control. RF: Have we detected every item we've tested, even though our sensitivity level is significantly above (20 to 30 db?) the limits we'd like to see. CN/RL: It's difficult to recall all details. Childers' MCB interface and some of Ford's reset boxes were not detectable. - Status of fiber from patch panel to anechoic chamber CN: Fiber from anechoic chamber to 140' is now working. A defective cable between the chamber and a splice room in the new building had to be replaced. There is no fiber on patch panel itself. - Status of equipment procurement CN: Have evaluated three spectrum analyzers thus far, and I'm presently working on a fourth. Still need to give HP a call. RL: I purchased two Mini-Circuits broadband amplifiers to drive the IF fiber link to the 140'. I also obtained two NRAO L-band amplifiers from the VLA. (These are units that were removed from their receivers in an upgrade.) - Summer schedule of meetings: RF: Any need for meeting over the rest of the summer? RL: Questions such as the calibration of the IF link to the 140 ft. come up periodically. These meetings are a good venue for discussing these types of items with Fisher and McKinnon. However, an e-mail forum would probably work for these types of things over the summer. Also, the spectrum analyzer evaluation will probably be complete in the next month or so. I am happy to lean heavily on Niday's recommendation; how much input do Fisher and McKinnon want on the selection? RF/MM: Niday and Lacasse can handle this. - Miscellaneous MM: The radio astronomy Iridium satellite tests have been postponed. Twelve satellites are now up, and nineteen should be up by the end of the month. There is a potential for interference with the radio astronomy band in the 1610 to 1614 MHz band since the satellites use the band from 1622 to 1626 MHz. The Quiet Zone issue of channel 64 has made some progress recently. We have received a design of an antenna from a consulting engineer. The antenna puts a null in our direction, radiating 2.5MW total, but only 15KW in our direction. This case set a legal precedent; it is the first case in which the Quiet Zone has had an effect on a transmitter outside the zone. - Next meeting: undetermined.