MEMORANDUM

TO: R. Fisher, J. Ford, F. Ghigo, R. Lacasse,  C. Niday, T. Weadon
FROM: R. Lacasse
SUBJ.: Minutes of Interference Protection Group 11-27-01 Meeting

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

Minutes of Previous Meeting

Approved.

Fisher brought in plots of interference seen during his L-band observations.  It is hoped that work on the Feed Arm Servo system will help this problem.

As noted last month, interference has been noted on the 40 ft. telescope when the GBT is moving at a high rate.  No work has been done on this problem yet.

1. RFI suppression of GBT equipment   (all)

Progress was made on the feed arm servo system interference.  Lacasse has ordered parts to filter and shield all cables except those associated with the motors.  A prototype filter box for the magnetostrictive transducers is presently being built in the shop.  A concept for a filter box to be built in the receiver room has been discussed with several people.  The basic idea to build this box around the existing cable shield to enable the addition of filters without long telescope down time.  McCullough has started to look at the motor problem.

With work winding down on the spectrometer and spectral processor, more time has been available to work on interference problems.

Work will start next month on the detailed design of the 300 MHz receiver.  Rosalind has completed work on the GBIP interface for the Interference Monitoring Station and will start doing the requested survey in January.

Norrod has been looking into using LabView to do an RFI survey.  Fisher will coordinate with Norrod to avoid duplication of effort.

A 26 GHz spectrum analyzer has been acquired on surplus by Acree.  Norrod has tested it.  Fisher will review the specs to check whether it is suitable for measurements at low frequencies.

Ghigo suggested that interference monitoring of the IF be automated.  Ford replied that Norrod has looked into this .  It is quite difficult to do because of the many IF channels and the flexibility of the IF system.

The M & S allocation for this fiscal year is $10K.  Also, there is $60K allocated for GBT RFI improvements.  There may be additional money available for large ticket items.

Jeff Acree is slated to start in January 2002.

One application for the junior RFI engineer position has been received, and it is quite good.  An interview will be set up in the near future.

Comments from Jewell were reviewed by some members of the IPG.  Jewell wants to expand the scope of the IPG to include external interference.  Jewell's comments were incorporated into a revised document by Ford, and will be sent back to Jewell for approval.

This item is in Jewell's court.

No news.  Fords stated that, to the best of his knowledge, all of our interference related requests have been incorporated into the building's plans.  Butch Wirt is keeping up with day to day construction activities for NRAO.  Ford will brief Wirt on our RFI requirements.

Efforts to interface the Advantest spectrum analyzer to the monitor station PC have been successful.  Rosalind has conquered the new GBIP interface!

Equipment is slowly being moved into shielded racks.

Software is being moved into the server which is now in the shielded room.  The goal is to be able to shut off computers in unshielded areas after hours.

Reception of the site radio is poor in certain places in and around the GBT.  Niday believes this is caused by a combination of signal attenuation and interference generated by GBT systems.  He will look into ways of improving reception.  One possibility is to add a repeater near or on the GBT.  It was noted that it should be possible for the operators to remotely control power to this repeater so that it could be easily shut off during observations..  Also, a preferred location for the repeater is under the surface, as the surface will provide some shielding for the radio astronomy receivers.