NATIONAL RADIO ASTRONOMY OBSERVATORY Green Bank, WV MEMORANDUM March 10, 1997 TO: R. Fisher, R. Lacasse, M. MkKinnon, R. Norrod, T. Weadon FROM: R. Lacasse SUBJ: Minutes of Interference Protection Group 3/7/97 Meeting In attendance: Fisher, Lacasse, McKinnon, and Weadon RF: Changes to minutes of previous meeting? All: No. RL: Format of minutes OK? All: Yes. RF: Comments on IPG web page? RL: Post minutes only after minutes are approved. MM: Observers are the main users of this info. Avoid filling the page with references to FCC reports and articles. Instead include a lot of site specific information. TW: Include interference sources found in the past. RL: Catalog by wavelength if possible. MM: Samantha's data is cataloged by 40MHz chunks already. The text accompanying the graphs needs some work before this is made public. Don Backer has changed his observing band due to information contained in Samantha's survey. RF: The web page will take the place of a memo series for the group. Is there anything that should not be posted? RL: Personnel matters. MM: Budgetary info. TW: Agree. RF: Might be best to be completely open. TW: There is a disk called /doc on yed that could be used to keep the web page. All: Decided to include links to computer readable documents contained in the list of reference documents distributed by Fisher at the last meeting. Discussion of Open Action Items: Interference reports: MM: No interference reported. Have recently written a document that was sent to Langley Air Force Base advising them of the details of the GBT relevant to their operation. In particular, the frequency agility of the GBT will usher in a new era of dynamic scheduling. They have been sensitized to our needs. RF: No call outs. RL: No call outs. Budget: TW: Who wants copies of requisitions. RF: I can keep copies of them in my notebook. So far have spent about 1K on antenna range items. TW: Some items needed by the IPG can be purchased with electronics M&S funds. Inventory: MM: Inventory completed by Wes Sizemore has been distributed to the group. Two items are worth noting. - We have two AR3000 25 to 2000MHz communications receivers. Liptak has stated that the one at the 140' is available to the IPG if they want it. - Sugar Grove has loaned us two kits each containing two calibrated antennas: a 300 to 1000 MHz LPA and a 30 MHz bowtie. These are on indefinite loan and may be useful in the indoor range. TW: There is a laptop in my office which can be made available to the group as well. Also, I have been told that CV has replaced all their 486 PC's with Pentiums, so there may be some compute power available there as well. RF: It would be good to get a request in for one of these. The laptop would probably not be useful on the sniffer cart. MM: Also note that the inventory contains several useful antennas. The 0.5 to 3 GHz cavity backed spiral may be especially useful. RF: We need to gather all this stuff in one place. TW: Can probably get a room upstairs in the old lab. ** Action item for Mark McKinnon to find space for equipment. RL: The inventory looks well done and was done quickly. Sizemore should be thanked. Requirements of monitoring facilities: RF: Updated document distributed today. Is it useful as is? RL: I think is should be adopted as a working requirements document. MM: Agreed. RF: Then we are ready for the block diagram design stage. RL: Would like to try to make some time available for this effort. RF: How best to split up effort. TW: Too busy with mock-up and other duties to be of much help. Can provide resources in the form of RF engineers and technicians, however. MM: Did some work earlier on GBT monitoring station. Can sketch up details to present to group. RF: RL to start on cart and indoor range. MM and RF to work on monitor stations. TW: Is it possible to share equipment between the monitoring station and the indoor range? RF: Since the monitoring station will be based at the telescope, I don't see much possibility for sharing. TW: Since electronics has a vested interest, it can fund some of the required test equipment. ** Action item for RL to start design of indoor range and cart ** Action item for RF and MM to start design of monitoring station. TW: A technician will be starting soon and will be available half time to help the IPG. RF: Part of this action item required that harmful levels of interference be specified for equipment in various locations. A document written by RF for Sizemore may be useful in this regard. Also Sid Smith will provide distances from various parts of the site to the GBT. Then a table can be made up listing locations and normalized power density. RL: Suggest the normalized distance be 10 meters, since this will be the common measuring distance in the indoor range. ** Action item: All to read and comment on above-referenced document. TW: Design reviews of the IPG facilities would be appropriate. All: OK. MM: This would also serve to increase awareness and interest. RF: Also, everyone will be using this equipment. Cable entry action item: TW: 240V is not used anywhere so won't be brought into the room. 208 3-phase will be brought in through the ceiling and down behind the absorber. It will be filtered like the 120V. The cable entry bulkhead drawing has been distributed. All connectors except for the 32 pin, 7A are here already. Two panels are being built. One is partially populated and is for immediate use by Norrod. The other will be fully populated and outfitted with pig-tails for easier access. For BNC cables, use N to BNC adapters since BNC connectors tend to leak. A single mode cable will be run from the indoor test range to the 140'. An Ortel 3GHz receiver/transmitter pair is available for the IPG to use, initially at the GBT receiver building and then at the indoor test range. A 10GHZ receiver/transmitter pair will be used to go from the mock-up in the lab basement to the 140'. RL: How will the spectral processor's SIG/REF signal be handled? MM: The SIG/REF is routed to the new building on a multi-mode cable. It's use can be shared with the mock-up TW: How much will this signal be needed by the indoor test range? RF: About 80% of testing can be done without a switch. TW: Why is switching required? RF: For difference measurements or calibration. TW: Could 1 PPS be used for switching signal. RF: In many instances. TW: An IRIG coax drop can be provided for this purpose if this would be accurate enough. RF: It would. We can always blank for a little while. "Items to be tested" action item RF: Revised list distributed. RL: Active surface electronics, which is on this list, has already undergone extensive testing. RF: Results can be reviewed by group. Other items: MM: Samantha will be returning this summer. She will continue work on identifying the source of interference in the radio astronomy band of 608-614 MHz. She built a YAGI and had just started testing it when she left. Is there more pressing stuff she should be working on? Her interests have shifted towards applied physics. Would appreciated additional ideas for tasks. RL: Want to do a dry run of the interference tests of the feed arm servo, some time soon. Need help with scheduling the spectral processor and running the spectral processor. MM: Can help. Next meeting: Tuesday, March 25, at 0800 in new conference room.