NATIONAL RADIO ASTRONOMY OBSERVATORY
                          Green Bank, WV


MEMORANDUM                                       November 10, 1998

TO:      J. Ford, F. Ghigo, R. Lacasse, R. Norrod, M. McKinnon,
	 C. Niday, T. Weadon
FROM:    R. Fisher
SUBJ.:   Minutes of Interference Protection Group 11/10/98 Meeting

In attendance:  Fisher, Ford, Ghigo, McKinnon, Niday, Weadon

Minutes of 10/27/98

     Approved.

Call Outs

McKinnon reported that Chuck has been searching for the source of
wideband noise bursts seen with the 610 MHz MIT array near the 300-ft
telescope site.  The bursts have approximately a 15 second period.

Review of action items

    L.O.'s, filters, and detectors for the anechoic chamber: Fisher
reported on a receiver system design for doing broadband noise
measurements between 30 and 1700 MHz in the anechoic chamber.  This is
a single conversion system with a selectable set of filters and
amplifiers.  He is now getting component costs.

    Monitor station design: Parts of the anechoic chamber receiver
design mentioned above can be used in the site monitoring station(s).
Ford said that he'd ask Dan Pedtke to help out where needed.

    Spending on this year's budget: Discussion deferred for the moment.

    Site radio system tests: The parts are in hand for low-band radio
and repeater tests to begin this month.

    Lab survey for RFI sources: No action as yet.

    Meeting with architect of new education center building: Ghigo
showed a first concept design from the architect.  The building location
is proposed to be on the east half of the airstrip with access from Rt
92.  The exhibit room and classroom would be shielded with possibly
RFI-absorbing passageways for entry and exit.  There are no windows
proposed for the exhibit room.  Suggestions were made on the type of
shielding material (1 or 2 mm copper mesh) and on the need for care in
filtering cable entries and keeping the shielded enclosure intact.
After the meeting Frank sent an email to the architect with our
suggestions and a recommendation of the book "Architectural
Electromagnetic Shielding Handbook" by Leland H. Hemming,

    Technical seminar of RFI suppression: Fisher said that he needs to
talk to Roger Norrod about RFI that might be coupled between components
within the receiver room before starting plans for a seminar.

    FCC Class B requirements and test procedures: No action recently.

    Air Force use of the GPS L3 transmitter: The VLA has been
coordinating their observing with the Air Force to avoid this
interference, and Wes Sizemore is now doing the same for Green Bank.
Mark will inquire about the frequency of use of this 1383.3 MHz
transmitter and whether the agreement on its use has changed.

    Publicly available version of RFI measurements of GBT equipment:
Niday said that this spreadsheet is now available and will prepare an
HTML version from time to time for posting on the IPG web site.

    GBT feed arm servo RFI measurements: Weadon reported that the fiber
and modems required for closing the door to the servo cabinet inside the
GBT receiver room are in the works.  RFI measurements inside the room
while driving the feed arm motors will then be made.  Cables between the
cabinet and the motors outside of the receiver room will not have their
shields terminated until they are finally installed after the feed arm
tip is lifted onto the GBT.  Nevertheless, RFI measurements outside the
room will be made while the room is on the ground to determine how
serious the suppression problem will be.

    Cal and sig/ref switching in the anechoic chamber: Nothing to
report.

    PC and workstation shielded test box: Construction is complete.  It
now needs a low cart to be able to move it around and to allow easier
access through the top.

Next meeting - Tuesday, December 8 at 8:00 am.