NATIONAL RADIO ASTRONOMY OBSERVATORY
Green Bank, WV
MEMORANDUM
November 17, 1999
TO: R. Fisher, J. Ford, F. Ghigo, R. Lacasse, C. Niday, T. Weadon
FROM: R. Lacasse
SUBJ.: Minutes of Interference Protection Group 11/16/99 Meeting
In attendance: Fisher, Lacasse, Niday, Norrod, Ford, Ghigo
Minutes of Previous Meeting
Call Outs for Interference
Action Item Review
1. Allocation of Remaining
IPG Funds for 1999
The remaining funds for this year will be spent on monitor station
components.
2. Site radio system
(Chuck)
The antennas are installed on the water tower. We are anxiously
awaiting feedback from users.
3. Microwave oven in shielded
test box (John)
The box will be assembled by telescope operators in the near future.
Ford reported that he is still unhappy with the construction quality and
will go with another vendor should we get into something similar
in the future.
7. RFI Considerations for the
New Tour Center
The building has been funded. Ford and Ghigo will interface with
the architect on the shielding of the building, and will keep the rest
of the IPG informed. The building funds probably cannot be used for
RFI research, but we may request some early purchases to begin testing
of shielding techniques needed for the tour center.
There has also been some discussion about using the Interferometer Control
Building for a tourist display. Since it is not shielded and very
near to several telescopes, the IPG is concerned about the RFI impact.
The group urged the use of passive displays to the extent possible and
the shielding of RFI sources using the same guidelines that have been adopted
for equipment being installed on the GBT.
8. Shielded Room Entrances
Fisher has measured the rooms (length, width, etc). This is a
first step in constructing a scaled prototype.
No progress on
other items on action item list.
Miscellaneous Discussion
Norrod urged that the IPG obtain information from Fred Crews about
possible sources of interference from contractor supplied equipment at
the GBT. He pointed out a few potential sources of which he was aware.
These include a thermostat in the pintle room, unshielded cables
across the telescope bearings, and various parts of the servo system.
Norrod also reported on the design of RFI doors for the three shielded
rooms on the telescope.
Norrod also reported on tests of the 100 MHz distribution system for
the laser range finders. Approximately 130 db of attenuation is required
at 200 and 300 MHz. this may be accomplished by a combination of
filters and shielded cabling. The 1500 MHz signal is too large and
difficult to attenuate to the required levels without major system modifications.
This will have to be dealt with later. Niday pointed out that many
components used by the cable TV industry may be useful to this application.
Next Meeting: December 21, 0800.