NATIONAL RADIO ASTRONOMY OBSERVATORY Green Bank, WV MEMORANDUM Sep. 22, 1998 TO: R. Fisher, R. Lacasse, R. Norrod, M. McKinnon, C. Niday, T. Weadon FROM: R. Lacasse SUBJ.: Minutes of Interference Protection Group 9/22/98 Meeting In attendance: Fisher, Ford, Lacasse, McKinnon, Niday, Weadon Minutes Approved. Call Outs Niday reported on a request from Behrens. During testing of the GBT prime focus receiver, interference at 500 MHz was seen. It was eventually tracked down to a signal generator in the OVLBI lab. Review of Action Items A list of action items culled from past meeting minutes was reviewed. Action items and comments from the meeting are reported in the paragraphs below. 1. Measurement of Receiver Room Shielding The room is ready for testing. The servo cabinet is shielded from the rest of the room. Cable shields are not terminated on the cabinet, however, so we should expect to see some interference from the servo system outside the room. Thus, carefully calibrated quantitative measurements of servo interference are not that meaningful at this point, although they would provide an indication of how much improvement is required from the proper termination of shields. Norrod is point man on this project. He and Simon will assist Niday with measurements. Weadon stressed that measurements with the antenna both inside and outside of the building would be useful. 2. L.O.'s, filters, etc. for the anechoic chamber Grammer has agreed to work on L.O.'s for the monitoring station on a time available basis. The same L.O.'s can be used in the chamber. Fisher's work on filters for the monitoring station can be extended to cover the filters needed here as well. Lacasse has not made any progress since the last meeting on detectors and post-detection filters. 3. Cheat sheet for anechoic chamber PC software A prototype sheet was distributed. The sheet was used during the demo at the end of the meeting. 4. FCC Class B requirements and test procedures Niday has downloaded some information on this. He also reported that there is a book in the library with detailed test procedures. 5. Quiet zone education initiatives The Quiet Zone web page has been updated with educational materials, and a form to make submissions easier to evaluate. Sizemore and Lockman have been to Randolph County to discuss upgrades to the emergency communication system with the fire department. Sizemore continues to inspect antennas installed in the Quiet Zone. This has the effect of educating the installers, and in some cases results in corrections to improper installations. A site tour for forty Cellular 1 employees is planned. A desire to participate in APCO meetings was expressed; this would be a good venue to educate people on the Quiet Zone. 6. Training of 140' operators on RFI database Balser has instructed all operators as well as Jerry Lawrence, the GBT chief operator, on the use of the software. Lawrence will make this training part of the routine training for new operators. 7. L-band receiver filters for Iridium and Glonass Fisher has spoken to Norrod about the requirements for Iridium filters. Norrod has obtained information on filters used at Arecibo and passed this on to Stennes. There has been no action on Minter's request for Glonass filters. 8. Fluorescent fixture specs for lab addition work No progress 9. Air Force use of the G.P.S. 1383.3 L3 signal No progress 10. RFI blanking signals to GBT backends (A) "OR" of internal and external spectral processor blanking (B) add "Blanking signal combiner" to the suite of GBT equipment No progress. Progress not imminent. 11. Monitor station design Fisher continues to make progress. Grammer has reviewed parts of the design and is commenting. 12. Publically available version of RFI measurements of GBT equipment Niday has created a new spreadsheet for this purpose, and will put new measurements of commercial equipment in it. Details of attenuation requirements for installation at the GBT, etc., will not be included as they are not relevant in this context. 13. List of items to be tested in anechoic chamber Niday reported that there are presently three things on the list: Childer's modified MCB box Schiebel's laser supply Pedtke's switching supply 14. Technical seminar on RFI suppression requirements and techniques Fisher will do this after receiver room measurements. 15. GBT feed arm servo system RFI measurements See (1) above. 16. Cal and sig/ref switching system for anechoic chamber No progress 17. PC and workstation shielded test box Progress continues to be made. The power entry box is nearing completion. Ford reported that Simon has ordered gasketing material that may have some uses on this box. 18. RFI suppression when/if interferometer control building is converted to a tourist facility Significant money has been appropriated for tourist exhibits recently. Whether they are housed in the ICB or elsewhere remains to be seen. Fisher reported that he has requested that a member of the IPG be on the committee that makes decisions about such matters. 19. Site radios Niday continues to gather equipment. Almost everything that is needed for a demonstration system is on-site. 20. GBT "harmful levels" document Comments received from various individuals have not yet been incorporated into the document. 21. RFI measurement mobile cart The cart still lacks a DC to AC inverter, batteries and an antenna mast. An inverter has recently been located. 22. Use of spectral processor in the anechoic chamber A network connection is still required in the chamber control room. Weadon to follow this up. Report on Measurements of 400 MHz PC RFI levels from a new Gateway PC have been measured. They are on file. Continuum PC Measurement System Demonstration The IPG group adjourned from the conference room and re-assembled in the anechoic chamber control room for a demonstration of Weadon and Schiebel's PC based continuum data acquisition system. Everyone was pleased to see that the system worked very nicely. Next Meeting Oct. 27, 1998, at 0800