NATIONAL RADIO ASTRONOMY OBSERVATORY
                 Green Bank, WV


MEMORANDUM                          May 26, 1998

TO:       R. Fisher, R. Lacasse, R. Norrod, M. McKinnon, C. Niday,
	  T. Weadon
FROM:     R. Lacasse
SUBJ.:    Minutes of Interference Protection Group 5/26/98 Meeting

     In attendance:      Fisher, Lacasse,  Niday

Minutes

     Approved as previously amended.

Call Outs

     None.

Site Radios

     Niday has contacted vendors about loaner equipment to set up a
demonstration system.  The priority of the site communication system
is lower than other tasks assigned to Niday, but these other tasks
should be completed soon.  Since the cost of a duplexer for a
demonstration system is about $1500, an alternative plan has been
developed: a receive station will be set up at the 140 ft., and will
be wired into the existing feed for the transmitter.  Once this system
is set up, tests of penetration into the GBT structure can be
conducted.

     Fisher pointed out that a repeater for the GBT area may be best
placed on the GBT alidade, to take advantage of the shielding by the
primary reflector of the GBT receivers.


Interference Reporting System

     The group agreed that it was time to start training the 140 ft.
operators on the use of this system.

On Using the Spectral Processor from the Anechoic Chamber

     There has been no time to work on the improvements discussed at
the previous IPG meeting.

PC based Continuum Detector

     A new A to D card has been purchased for this system.  It seems
to work much better than the previous one.  Supporting sampling rates
of at least 20 KHz appears feasible.  Weadon will continue to work on
this.

GBT Receiver Room Test

     Many devices have been characterized for RFI over the past year.
However, not many have had much follow up work to improve their
emission spectrum to meet our design goals.  One of the biggest
unknowns has been the shielding effectiveness of the GBT receiver
room.  Devices in this room are very close to the receiver, and as a
result have very stringent RFI requirements.  Part of the shielding
for devices in the receiver room will come from the room itself.  The
amount of shielding has been a big unknown for a long time.  To
quantify this unknown, a test of the receiver room will be carried
out, hopefully this summer.

     Equipment required for testing from 30 MHZ to about 12 GHz is
available on site.  Swept frequency measurements over a good part of
this range will be carried out.  This will need to be coordinated with
CRSI, since some modifications to the room are required before it is
ready for testing.  
=

****Action Item: Fisher to notify Hogg of coordination requirements
for GBT receiver room shielding effectiveness testing.

EMC Seminar

     The possibility of having a shielding and filtering seminar was
discussed.  Topics to be discussed would include the IPG design goals
and methods that have been successfully used to meet them.  It was
decided to schedule this seminar after the shielding effectiveness of
the GBT receiver room has been measured.

View Graphs Available

     Fisher has View graphs available from an ATNF seminar on EMC.
These are available for anyone who would like to see them.


Next Meeting

     June 9, at 0800.