July 23, 2002
TO: J. Acree, C. Beaudet, R. Fisher, J. Ford, F. Ghigo, R. Lacasse,
R. McCullough, C. Niday, W. Sizemore
FROM: Z. Manganello
SUBJ.: Minutes of Interference Protection Group 7-23-02 Meeting
In attendance: Acree, Beaudet, Fisher, McCullough, Niday, Sizemore,
Ford, Lacasse, Emerson, Ostaff, Manganello
Minutes of Previous Meeting
LIGO Group Visit (Ford)
The Laser Interferometer Gravitational Wave Observatory (LIGO) group will be here on Thursday. LIGO has two observatories – one in Washington and one in Louisiana. They are attempting to detect gravitational waves, but are having trouble getting the sensitivity necessary to detect this phenomenon. This is a very difficult measurement to make. Rick suspects they are dealing with conducted rather than radiated EMI. Their apparatus consists of three mirrors making an “L” shape, each separated by 4 kilometers. The mirrors are acoustically isolated, and the baselines are orthogonal so they can detect waves from any direction. This project was apparently in competition with the GBT for funding.
There was some discussion on how we can help LIGO. We looked at the proposed agenda for their visit. Rick recommended that we could have a brainstorming meeting to solve specific issues around 1500 hours. John thought it might be nice if they forwarded us specific questions. It seems that the LIGO group doesn’t really know what they’re dealing with yet, so they aren’t in a position to pose specific questions. We do want to make sure they see the chamber. Jeff will talk to Anish to get him involved. LIGO may have to design their own data acquisition system.
We have committed to spending as much time as LIGO wants. Some discussion on how much cooperation we should give them.
Windows in Shielded Room (Acree, Ostaff)
We have completed baseline RFI testing and determined that the windows are a weak point. The four windows in the equipment room have been removed and are being reworked. Because of corrosion from dissimilar metals, the hats and flats have been sent off for electroless nickel plating. New locking brackets have been designed to hold the window together and block RFI. Prototype brackets have been made for one window and the remaining brackets for the room are in production now. Galvanically compatible conductive adhesive will be used.
Shielded Room Status (Acree)
The shielding effectiveness testing was well worth the trouble,
for that data is proving very useful to us now. We are now working on the
windows because they appear to be the biggest problem. There was some concern
that perhaps the whole shielded room was useless, but it seems that by
fixing trouble spots we should be able to achieve the 60 dB specs. The
electroless nickel plating won’t corrode. There was some question about
the electrical bonding of electroless nickel, but after some testing we
are satisfied it will work. A statement of work has been sent to the plating
company in order to make specific our requirements. We will be putting
copper-nickel flectron around the windows, which is much less prone to
corrosion than the copper flectron that was used before. We will also use
a synthetic non-water based adhesive, and we will use it more sparingly,
which should cut down on galvanic action. Hopefully these changes will
fix the room for both the short and long terms.
Schedule: flectron will go on today, hats and flats will probably be in early next week, and the locking brackets will probably be done by early next week.
Discussion – the flectron will be used to tie the window copper to the copper paint. We might be able to get some high school students to assist in further testing. Denting the copper tape might get the copper through the adhesive and make a better bond.
Metrology System (McCullough)
Electrical upgrades to the first unit are finished.
RF box will go to Bill R. to be sealed up.
One set of cables needs to be made.
The whole thing could be ready to go back in the chamber in the first week of August.
Hopefully testing and upgrades will be done by the middle of August.
The unit should be ready to go to the field in the end of August.
Feed Arm Servo (Lacasse)
Boxes to filter and shield have taken a back seat to work on the
windows in the shielded room.
A prototype box in which to put filters is finished. A section of the filter panel has been made and tested. The shop has the go to build the full panel.
Talking to Jeff Cromer about where the brackets will go in the receiver room.
3.6m RFI Dish (Fisher, Manganello)
Rick knows the history behind this system. We originally got it
about 1 ½ years ago since we had some extra money and we wanted
to make satellite measurements and get more angular resolution. It has
been in storage until about a month ago. The BYU people have SRTS very
similar to this system, and they will help install the dish, particularly
getting the controller and the satellite prediction software up and running.
The status report is as follows:
(1) All available documentation regarding this dish has been collected.
(2) An installation site near the Deer Stand has been selected and flagged.
(3) The majority of required hardware has been ordered.
(4) The antenna, mount, wind trusses, quad poles, and feed cover have been moved to the subreflector storage shed.
(5) A work request has been put in for installing the mast, conduit, and digging the ditch.
(6) Zach and Steve surveyed the C’ville site to learn from that installation.
(7) A temporary stand for the mount assembly has been built by the machine shop.
(8) Underground cable runs in the vicinity of the Deer Stand have been located and marked.
(9) A survey of transmission line on site was taken, and pros and cons of each were discussed. We decided on using three runs of ½” heliax.
(10) A low cost manual antenna positioner for installation and test purposes has been ordered.
What remains to be done is as follows:
(1) Complete EMI testing and shielding of the DC motors on the mounts.
(2) Find or purchase control cable for the positioner.
(3) Decide on conduit
(4) Prepare the 4 ½” pipe for installation when it arrives.
(5) Find a PC to run this system.
Carla has been testing the DC motors, which generate considerable RFI.
With some modifications, the motors have been much improved.
New Tour Center (Jeff)
Jeff went to the meeting since John wasn’t available that day.
The three main problems encountered are:
(1) Ballasts for the overhead fluorescent lights.
(2) Lindgren and the prime contractor are having trouble reaching concurrence.
(3) Shielding the power box for the electrical room.
Shielded doors on the GBT are just metal architectural doors with gaskets.
We. might consider doing IEEE testing on those doors to see if they work.
Ballasts are probably pretty quiet by themselves. The T-8 tubes and wiring are comparatively much noisier.
Discussion on using 4-lamp Centium ballasts or two two-lamp Powrkut ballasts.
Perhaps use the Centium with RF-1 filter?
Jeff will try to find out how many ballasts will be needed and where they will go.
We would like to test the 3 and 4 lamp fixtures. Ideally we should test the devices which will actually go into the building.
Several people from the IPG should look at the shielded room document review.
Discussion on the possibility of pulling the spare frame out of the control room and using the associated shielded door we have in storage. Probably not a viable option – it’s too late and doesn’t fit the budget.
FS202s and Computers (Carla)
No recommendation on this yet, just data collected so far. Ed
said that it might be that computers are noisier than the FS202. Carla
has begun designing a way to quiet the FS202 device. A few models of laptops
were tested in various configurations; it seems to be the case that the
computers are noisier than the FS202s, so effort to quiet the 202s might
be wasted. Notebooks turned out to be noisier than desktops, and flat panel
monitors seemed to be noisier than CRT monitors. There may have to be some
discussion on computer policy (turning machines off when not in use or
during low frequency scans, etc.).
Security Cameras (Carla)
We now have a proposal to install security cameras by the GBT
and the Jansky Lab. Jody and Mike were told the cameras are shielded, but
we found the cameras fail RFI testing. Carla provided recommendations and
the vendor said he would fix the RFI problems before selling to NRAO.
We already have a shielded close-circuit camera that Tim quieted. The system was not extremely high quality, and this new system is fully integrated and has nice control software.
Chuck suggested we check to see if they have an audio system that goes with the cameras.
Discussion about the merits (or lack thereof) of using conduit for shielding.
Discussion on spending money out of remaining accounts before
the end of the fiscal year (Sept. 30th).
Discussion on the availability of a large Orbit positioner at NAIC. Could be useful for an open air test range. Weighs 1800 lbs. & is in good condition. It’s a 1986 model with about 1000 hours on it. It is currently in New York.