NATIONAL RADIO ASTRONOMY OBSERVATORY
Green Bank, WV
August 10, 1999
TO: R. Fisher, J. Ford, F. Ghigo, R. Lacasse, C. Niday, T. Weadon
FROM: R. Lacasse
SUBJ.: Minutes of Interference Protection Group 08/10/99 Meeting
In attendance: Fisher, Lacasse, Niday
Minutes of Previous Meeting
Approved, although there was some discussion as to exactly when the
blanking modifications to the continuum detector could be put off.
They will be done at the earliest opportunity, although it is unclear when
that will be.
Call Outs for Interference
None. With the 140 ft. telescope now retired, perhaps this
item should be taken off the agenda.
Action Item Review
1. Blanking and sig/ref
switching system system for anechoic chamber (Rich, Chuck, Rick)
Fisher reported that Weadon has started work on modifications to the
blanking software in the continuum detector. A system to switch AC
power on and off for the Quadrant Detector Laser Supply and Feed Defroster,
without generating its own RFI, is still required and will be developed
as time allows.
2. Site radio system (Chuck)
An application for temporary authorization to transmit has been filed
with the FCC.
3. Microwave oven in shielded
test box (John)
4. Shielded room entrances
Coax for the water tower has been ordered and received.
Arrangements to mount antennas on the water tower will be made shortly.
There are still problems with isolation between transmitters.
Separate antennas for each transmitter may be used, or coax hybrids may
No real progress. Fisher stated that the intent is to build a
10:1 scale model which can be tested in the anechoic chamber by placing
a dipole or monopole antenna in the model room.
5. Monitor station and anechoic chamber
developments (Rick, Rich)
The L-band horn for the monitor station is out of the shop, and needs
to be installed. Other developments await personnel availability.
6. Progress on suppressing
RFI from equipment that has been measured in the anechoic chamber
The laser group is attempting to implement some of the suggestions
received from the IPG.
11. RFI survey plan for GBT Commissioning
The laser supply for the quadrant detector was measured again and failed.
For the next iteration, the DC supply will be packaged and shielded separately
from the laser supply and additional filtering will be installed.
The Spectral Processor was used for this test. It was noted that
its use is still a bit tedious. Fisher plans to further improve the
interface. During these tests radiation from the DC power supply
for the test antenna amplifier was noted. To eliminate it from the
measurements, the amplifier and supply were moved out of the anechoic chamber.
During a recent meeting, performing an RFI survey over
the GBT observing bands was deemed desirable. Fisher is slated to
generate a list of requirements for accomplishing this. The requirements
are basically those for the GBT monitoring station. Feeds and amplifiers
for all bands can be purchased (at least in theory) and the GBT LO and
fiber systems can be used to transmit the signals to the spectral processor.
No progress on other items
on action item list.
Next Meeting: August 24, 0800.