NATIONAL RADIO ASTRONOMY OBSERVATORY Green Bank, WV MEMORANDUM October 15, 1997 TO: R. Fisher, R. Lacasse, R. Norrod, M. McKinnon, C. Niday, T. Weadon FROM: R. Fisher SUBJ: Minutes of Interference Protection Group 10/15/97 Meeting In attendance: Niday, Fisher, McKinnon, and Weadon (notes from Lacasse) Minutes Minutes from the last meeting were approved. Comments on the new format were quite favorable. RFI call-outs McKinnon reported on interference experienced by Lynn Matthews at the 140-ft at 1400 and 1407 MHz. The 1400 MHz radiation was traced to a laser ranging module just to the south of the telescope. This is thought to be the 14th harmonic of a 100 MHz oscillator in this module. The 1407 MHz signal was fairly weak, and its source was not determined. Action item: McKinnon will meet with Dana Balser to determine the best way to set up an RFI reporting system at the 140-ft. Equipment procurements Niday said that the purchase order for the model MS-2602 Anritsu (spelling?) spectrum analyzer is in the works. It has a slightly higher noise floor that its competitors, but all other features are comparable, and its cost is about $6K cheaper - purchase cost around $26K. This leaves about $4K in the combined 1997 RE and operations budgets for the IPG. Weadon and others are reviewing this year's total budget situation and invited the IPG to submit a new budget for 1998 with the possibility that some items can be purchased in 1997, even beyond the $4K specifically allocated for the IPG. Known items to go into the new budget are a power meter, a reference switching system for the anechoic chamber, a UPS/battery system for the mobile cart, and parts for the first monitoring station. Action item: Fisher will poll the group for budget items. GBT equipment tests The GBT project is adjusting its technician resources to cover construction projects, and this may affect the fraction of time that Niday spends on anechoic chamber measurements. McKinnon and Weadon are aware of the need to maintain momentum on the anechoic chamber work and will be discussing the priorities with this in mind. The recent GBT electronic review committee emphasized the importance of controlling the RFI emissions from equipment around the GBT. Corrective actions for RFI emissions found from equipment that has been measure so far has generally been good, but renewed emphasis may be appropriate in specific cases. General action item: Make sure that list of equipment that needs to be run through the anechoic chamber is up to date. School LAN tests and installation. Two Mac computers and a representative sample of the LAN wiring to be installed in the Green Bank School were tested in the anechoic chamber and an e-mail report sent to John Ford. No one at the meeting was aware of the status of the installation at the school. Mobile RFI measurement cart The need for a communication receiver or the mobile cart is not pressing at this time. The spectrum analyzer has a detector and speaker so we'll wait for more experience with the cart before budgeting a separate receiver. Site monitor station Fisher reported that Rich Bradley will design an amplifier/antenna module to meet the requirements of the site RFI monitor station while he is designing similar modules for the array feed project. Fisher will continue working on more design details of the rest of the monitor electronics. Workstation and PC shielding Construction of the "complete shielding" test enclosure for workstations and PC's is expected to be completed at the end of October. The philosophy behind the enclosure is to establish a baseline for total shielding of the device and attachments (only a filtered AC input line and metalized window for the monitor). Each attachment (keyboard, disk drive, monitor, etc.) will then be moved outside the box to determine how much it contributes to RFI radiation and what filtering/shielding measures are required to suppress that RFI. Next meeting date October 29th. Due to individual conflicts and holidays in November the meetings for that month will probably be combined into a single meeting in the week of Nov. 17-21. McKinnon and Fisher will coordinate with GBT meeting.