NATIONAL RADIO ASTRONOMY OBSERVATORY Green Bank, WV MEMORANDUM February 17, 1997 TO: R. Fisher, R. Lacasse, M. MkKinnon, R. Norrod, T. Weadon FROM: R. Fisher, R. Lacasse SUBJ: Minutes of Interference Protection Group First Meeting Fisher, Lacasse, McKinnon, and Weadon met for the initial meeting of the Interference Protection Group on Feb. 14, 1997, from 9:00 to 11:00 AM. General discussion of the charge to the committee: The IPG will be mainly responsible for control of on-site interference at the Green Bank Observatory, and Wes Sizemore will administer the quiet zone and handle off-site interference (power lines, devices in the community, etc.) under Mark McKinnon's supervision. The mobile monitoring vehicle(s) will continue to be part of the Quiet Zone administration. Detailed allocation of existing equipment remains to be defined pending an inventory. First call on interference reports from the telescope will be this group's responsibility as defined below. After further discussion and clarification of issues there was general consensus on the charge to the committee as appended to these minutes. The amount of work that could be started would be enough to keep at least one person busy full time. Rick stated that he felt that committee members should expect to expend 20% of their effort on the IPG. The budget for 1997 is $15,000. Available technician help will probably increase in the second half of this year, but we may be able to count on one day a week from the electronics division to start. Our intention is to involve telescope operators to the greatest extent possible. New equipment requirements await an inventory of existing equipment and definition of new measurement capabilities. The main items to be immediately addressed by the group are: 1. Outfitting the indoor test range for measurement of RFI from Observatory equipment, particularly equipment to be installed on the GBT. 2. Construction of monitoring stations at selected sites around the Observatory and transmission of their signals to common location(s) for immediate display of the interference environment around the site. The objectives are faster response to interference reports from observers, allowing telescope operators to make a first pass at determining the source of interference, and increasing the sensitivity of our monitoring system. 3. Outfitting a mobile interference detection cart for finding interference generated in the lab or other buildings with potential RFI producing equipment. 4. Begin a program of testing GBT equipment in the mockup for internal spurious signals. A first estimate of the sort of equipment that we expect to assemble for interference detection/monitoring are: 1. One or more spectrum analyzers. There are a couple of old analyzers that may be available, but it is not clear whether they are stable enough to be useful. 2. Continuum detectors for wideband and impulsive noise. One of the old DCR's might be a source of amplifiers and square- law detectors and serve as a sensitive continuum test setup. To this we would add moderately fast sampling (< 1 ms) with a PC for impulsive noise analysis. 3. A PC for measurement automation, particularly at the indoor test range. 4. Antennas, preamps, L.O.'s for the monitor stations and mobile cart. Coverage from 100MHz to 1500MHz is crucial. Coverage from 25MHz to 3000MHz is desirable. 5. Fiber modems and multiplexers to transmit signals from the site monitor stations to the spectral processor or central spectrum analyzer. Initially, we may be able to piggyback or time-share existing fiber systems in place at the Jansky lab, GBT receiver room, and interferometer control building. 6. At least one monitoring station with near-instantaneous direction finding capability in conjunction with the spectral processor. The first station will probably go at the 140-ft and serve as a prototype for the GBT monitor antenna system. 7. A filtered cable entry panel for the indoor test range for RF, digital signals, and AC and DC power. One panel will be made up and one blank panel provided for future additions. We need to define documentation standards for test measurements, interference diagnostics and identification, and general interference environment data. The latter is well under way with Mark's and Samantha's data base. Telescope operators need to kept current on the history of interference monitoring and diagnostics. We need a central clearing point for this information. One person needs to be responsible for all indoor range test data and its archival and distribution. In the short term, the group needs to decide whether to request additional capabilities of the GBT IF system, or to simply piggy-back on the resources as designed. In particular, fibers will be difficult to add after the completion of construction; should part of the group's budget be allocated to a few additional fibers? Obviously, this decision must be reached before the purchase of fibers. Action items: 1. For the time being, the interference diagnostics call-out list will be McKinnon, Fisher, Lacasse. The telescope operators will be notified by Mark. The long range goal is to train telescope operators to do initial diagnosis and to identify a technician to take some of the call-out responsibilities. Mark will begin operator training as required. 2. Mark will ask Wes Sizemore to inventory his monitoring equipment and Mark will identify items that are appropriate for sharing between on-site and off-site monitoring. 3. Rick will define sensitivity and frequency range requirements for monitoring and test equipment for the indoor range, mobile cart, and monitoring stations. Rich and others will then begin design and implementation, including the identification of existing lab equipment that can be used for these purposes. Wes can probably use a better impulsive noise detection scheme for power line monitoring. 4. Rick, J.D., and Mark will develop a user interface to the spectral processor for RFI diagnostics as part of the GBT observer interface task. 5. Mark will clean up documentation of the interference data taken with the spectral processor on the various 140-ft receivers. The data are available on the Web and will be more widely advertized. 6. Rich volunteered to be the keeper of meeting minutes. Rick will check with Jay on whether he wants to be on the distribution list. Roger will be copied on most activity. 7. Tim will begin design on the indoor range cable entry panel. A rough guess at what is needed includes feedthrus for AC, digital signals (`2 DB25's), a few 1A DC connectors, fiber entries, and a spare panel. 8. Roger Norrod has offered to draw up a list of GBT equipment that needs to be tested for RFI. 9. Tim will inventory available fiber optic receivers and transmitters. A list of interference reports, memos, articles, and other documents was distributed to the group members. The group meeting schedule will be 8:00 am on the same Tuesdays as the GBT coordination meetings (2nd and 4th Tuesdays of each month) beginning with Feb. 25, at least until we determine the optimum meeting frequency. For the record, the following is the charge to the committee, as agreed upon by Fisher, Lockman, and Norrod. Interference Protection Group The Green Bank Interference Protection Group is responsible for minimizing the radio frequency interference to astronomical observations from equipment and activities at the Observatory and for developing techniques for removing or avoiding RFI that arrives from sources outside the Observatory. To this end, and within the time and resources available to the committee, it will 1. Improve the sensitivity and direction finding capability of interference monitoring equipment. 2. Improve the response time to reports of interference from observers to find and correct sources of RFI from within the Observatory. 3. Provide the telescope operator(s) with timely information on the spectrum environment at critical points around the Observatory so that new local sources of RFI are quickly detected and corrected. 4. Survey new and existing Observatory equipment for internal or radiated interference as it may affect astronomical measurements and take or request corrective measures as required. 5. Continue to build databases on the Observatory's interference environment and make that information readily available to observers for planning observing programs. 6. Provide assistance to the administrator of the Quiet Zone to the extent afforded by on-site monitoring and direction finding equipment and databases and where Committee expertise might be helpful in particular Quiet Zone technical matters. 7. Provide training and documentation to telescope operators and other technical personnel whose duties affect or are affected by local interference. 8. Develop or adopt new methods of removing or reducing the impact of interference that inevitably appears in astronomical data.