NATIONAL RADIO ASTRONOMY OBSERVATORY
Green Bank, WV
July 6, 1999
TO: R. Fisher, J. Ford, F. Ghigo, R. Lacasse, C. Niday, T. Weadon
FROM: R. Fisher
SUBJ.: Minutes of Interference Protection Group 07/06/99 Meeting
In attendance: Fisher, Ford, Niday, Weadon
Minutes of Previous Meeting
Call Outs for Interference
Action Item Review
of OVLBI transmission field strengths at the GBT.
The initial measurements from the GBT control room deck are waiting
for someone in the IPG to get time to assemble the equipment. For the
moment, Chuck is the lead person on this item, but we'll review the
assignment according to work load in a month or so.
2. Site radio system (Chuck)
A hybrid combiner is on order to put two transmitters on the same
antenna. Progress on mounting the antenna on the water tower has been
slow so an alternative test site may be considered.
3. Monitor station and
anechoic chamber developments (Rick, Rich)
Conctruction of the outdoor monitor platform to the west of the
45-ft is nearly complete, and the three Cas A experiment antenna poles
have been set around the platform. Underground coaxial cables have been
run fron the three Cas A antennas to the platform. One of the 30-120
MHz Cas A antennas will eventually be mounted on a 2-axis positioner to
serve double duty as a low frequency direction finding antenna. The
(expensive!) stainless steel box to house the platform electronics is on
order. A place to terminate the three optical fibers from the platform
in the GBT equipment room is being coordinated with Bob Simon and Roger
4. Microwave oven in shielded
test box (John)
The shielded enclosure was located in the warehouse and returned to the
manufacturer for rework.
5. Shielded room entrances
The 7 GHz absorber has been received. Drawings for model entrances
need to be made after looking at the possible configurations in the
second floor hall and control rooms.
6. Progress on suppressing
RFI from equipment that has been measured in the anechoic chamber
Work on shielding continues but nothing specific to report. Fisher
and Niday need to write a report on how much additional suppression is
required for equipment that has been tested.
7. Telescope operator
participation in IPG activities (Rick)
Eric Knapp has been given the task of finding a data base for
plotting the buildings and geography around the Green Bank site for use
in a display of RFI monitor station direction finding radials.
8. RFI considerations
for new Education Center (Frank)
9. RFI survey plan for
GBT commissioning (Rick)
10. GBT RFI 'harmful levels'
11. Lab RFI suppression
12. Interference at
13. RFI monitor for
14. Cal and sig/ref switching
system system for anechoic chamber (Rich, Tim)
Tests of the continuum detector system and sig/ref switch in the
anechoic chamber showed that a blanking option needs to be added to the
PC software. The blanking time will be specified by the user in
seconds. Some work may need to be done to clean up the test electronics
to allow measurement of switching transients from equipment under test
without blanking. A computation and display option of (sig - ref) / ref
will be added to the software.
15. FCC Class B requirements
and test procedures (Rick, Chuck)
Requirement for a turret for anechoic chamber
Next Meeting: July 27, 0800.