Green Bank, WV


Aug. 28, 2001
TO: R. Fisher, J. Ford, F. Ghigo, R. Lacasse,  C. Niday, T. Weadon
FROM: R. Lacasse
SUBJ.: Minutes of Interference Protection Group 08-28-01 Meeting

In attendance: Fisher,  Ford,  Ghigo,  Lacasse,   Niday

Minutes of Previous Meeting

Interference Reports
Interference with three fairly broad peaks was observed with the GBT between 2330 and 2340 MHz.  The group speculated that the source might be an audio broadcast satellite.  Also observed on the GBT was some strong RFI somewhere between 9250 and 10250 MHz.  It appeared to be pulsed, at about 4 to 5 pulses per second.  The RFI began around 10 am or so on Aug. 25, 2001.  Total power plots of this interference were provided by Balser and are available in Lacasse's office.

There was some discussion about whether the RFI reporting system was too difficult to use, and whether the observer should be asked to submit reports.  The consensus of the group was that it is very important that RFI reports be filed.  There are probably ways of greatly simplifying the reporting process.  For instance, one mouse click could cause the all outputs of an observation to be stored in a special directory to which the IPG has access.  The other side of the coin is that once these reports are generated, someone will need to act on them...

Review of Action Items:

   1. Interference Manager position status (John)

Two promising applicants have been interviewed, and one more is scheduled to be interviewed tomorrow.  We should be ready to extend an offer by the end of the week.
  2. End-of-year purchases (all)
There was some discussion of priorities in spending available funds.  A decision was reached to buy a spectrum analyzer with frequency coverage to 10 GHz to allow monitoring of any part of the GBT IF band from the control room.  Also a decision was made to purchase a lightning monitor for the GBT control room.  Antennas to cover bands above 1 GHz are needed both on the GBT monitor station and in the anechoic chamber.  If time allows, suitable antennas will be identified and purchased.  Finally, it was decided to have the IPG spectrum analyzer calibrated.
  3. RFI considerations for new Education Center (John, Frank)
The design is now mostly settled and some work is in progress to reduce the cost of the building.  The RFI consultant says that the cost cutting measures have not impacted the RFI integrity of the building.
   4. Site-wide interference suppression policy - position  paper (John, Rick)
Phil has read it.  No comments yet.
   5. RFI suppression of GBT equipment   (all)
Quite a bit of testing of the Laser Ranging System control boxes has been done.  A filter retrofit has been designed for these boxes.  Parts have been ordered and drawings have been submitted to the shop.  Work is presently on-going to suppress RFI from the laser-ranging instrument itself.

Quite a bit of progress has been made on suppressing RFI from the ultrasonic anemometer, and it still appears to function as an anemometer!  Testing has shown that while the installed filters imporved performance, it still does not meet the CCITT limits.

Little progress was made on the servo system length transducers.  It was reported that suitable filters for the units have been found and will be ordered shortly.

Ford will set up a meeting with Bignell and Jewell to discuss the RFI implications of moving some operations into the GBT warehouse.

  6. Progress on suppressing RFI from equipment that has been measured in the anechoic chamber
One of the weather stations has been repackaged in a metal enclosure and filtering and shielding have been added to key subsystems.  Niday has also certified this unit as being acceptable for use.

Network equipment in the new wing of the lab is being repackaged into a shielded rack.  This should be complete in a few weeks.

Software applications are being moved to the server at a fairly low priority.  This will allow more workstations and PCs to be powered down when not in use.

   7. Monitor station developments (Rick)
White and Shank have completed the construction of the monitor station near 85-1, and it appears to be working quite well.  Software controlling the rotor is a bit flaky (summer student project) and will be upgraded by Fisher.  The station can monitor two bands: 200 to 1000 MHz and 1200 to 1700 MHz.
   8. Measurements of PC/Workstation in a shielded box (Chuck)
The box is presently being used for the tests of the servo length transducers described in (4) above.
 Next Meeting:  September 18, 2001