TO: J. Acree, C. Beaudet, R. Cutshall, R. Fisher, J. Ford, F. Ghigo, R. Lacasse, R. McCullough, C. Niday, W. Sizemore
FROM: R. Lacasse
SUBJ.: Minutes of Interference Protection Group 2-19-02 Meeting
In attendance: Acree, Beaudet, Fisher, Ford, Ghigo, Lacasse, McCullough, Niday, Sizemore
Minutes of Previous Meeting
1 - Reported-RF tracking data base (Jeff)
Acree distributed an update of the spreadsheet that was distributed at the previous meeting. He has enhanced it as suggested at the previous meeting and added a legend page which defines all the acronyms. At this time, the spreadsheet is being used as a minimal database. A goal is to migrate the information to a better database when resources allow.2 - 300-400 MHz search and clean-up (Jeff, Carla)
Acree tabulated information contained in Anish's report of GBT measured interference in this band. Acree's table is ordered by frequency and contains relative power information for each frequency. It was noted that the accuracy implied by the number of decimal places in the frequencies is deceiving. All numbers refer to the center frequency of a band of frequencies 40 KHz wide (analogous to the center frequency of a 40 KHz bandpass filter).3 - Interference to pulsar observing around 1400 MHz
Frequencies emitted from the weather radio's receive port were measured and tabulated. Twenty-four harmonically related frequencies were measured from 50.54 MHz to 1212.99 MHz. There was a consensus that a bandpass filter ought to be added to the radio's receive port. In general there was agreement that any equipment connected to an antenna ought to be scrutinized. Sizemore was asked to check his radios.
Brackets for installing the 70 - 1000 MHz antenna at the Deer Stand are nearly complete. Possibly the antenna can be installed tomorrow. This will free the smaller 200 - 1000 MHz antenna, which can then be used for RFI searches in the lab.
It was noted that Fisher has recently distributed a report on RFI measurements with the Deer Stand. The report showed that a great deal of interference in this band was coming from the lab. This was demonstrated by taking measurements with the antenna pointed at the lab, and with the antenna oriented such that the lab was in a null of the antenna. Acree pointed out that since Anish's and Fisher's data were taken at different times, one could extract persistent and transient RFI from the data.
Fisher also reported that he had recently completed a scan in azimuth using the Deer Stand monitor station and the spectral processor. A report should be available soon.
Beaudet reported that she has been working on the PC that is used to control the 40-ft. antenna and acquire data there. The PC has been grossly modified and has lost all of its shielding. The group made several suggestions ranging from installing the PC in an industrial case to replacing it with a surplus, TEMPEST qualified, PC. Heatherly and Maddalena are contacts for the PC. The PC is scheduled to be used in March.
Filters are on order for the the atmospheric phase interferometer.
FiberCom WhisperLan ethernet transceivers are being replaced.
An MIT experiment which was recently identified as being a source of interference has been turned off with the agreement of the PI.
The bookkeeping PC at the Interferometer Control Building will be moved to the cable building this summer when modification to that building are complete.
No progress.4 - Feed arm servo (Rich, Randy)
McCullough reported that a representative motor and controller are almost ready for testing. Filters for the motors have long lead times from Spectrum Control. Other vendors, including LCR and RTRON, have been contacted.5 - Lasers (Carla, Randy)
Acree noted that he has a good contact at NSWC who is an expert at terminating cables to contain RFI.
Lacasse reported that RFI enclosures for the filters for the magnetostrictive enclosures have been received. A good lesson learned during the construction of these boxes it that the shop prefers not to weld smallish aluminum boxes. It would have been far simpler, and cheaper in the long run, to mill the boxes out of solid stock. This would also yield better mechanical and possibly better RFI properties.
Shelton is assembling a complete unit. When it is complete, the IPG group will have it modified. All parts for the modifications are on order. Taggart is working on drawings which will soon be sent to the shop. One loose end is that the design for the laser enclosures is not complete. This will impact the modifications. Ford will push to get this design finalized.6 - Boltec lightning detector (Chuck, Carla)
Niday has requested information from the manufacturers to allow him to filter signals going to the antenna of this unit. The manufacturers are not returning his calls. Some reverse engineering may be required.7 - HVAC radiation around 43 MHz
No progress.8 - DGS laser system data acquisition module
The laser group is in the process of shielding and filtering these.9 - Blue warning lamps
The operations group will replace the blue warning lights with ones recommended by McCullough. In addition, the amber warning lights on the laser control modules are designed similarly to the present blue warning lights. They will be replaced as well.10 - Main GBT drives
Heatherly has noted interference at the 40-ft. telescope from the GBT when the GBT is moving. The interference seems to be worse when the GBT is pointed away from the 40-ft. Fisher will attempt to duplicate and expand (by adding frequency information) on the measurements using the Deer Stand monitoring station.11 - Anechoic chamber turntable (Jeff, Carla)
Beaudet has one and will test it shortly. The unit is manufactured by Scientific Atlanta and can handle a 100 pound axial load. Beaudet will speak with Egan about the possibility of obtaining a fiberglass table for it. It was noted that the bulkhead between the anechoic chamber and the control room is getting quite full; it is not clear whether it can handle all the cables from the turntable and the new antenna measurement equipment.12 - Call-out procedures and assignments (Jeff, John)
Acree, Beaudet and Sizemore will handle callouts. Sizemore will take the lead, due to his experience in this area, and will use callouts as training opportunities for Acree and Beaudet.13 - Site-wide interference suppression policy status (John)
Acree is to review this paper and return it to Ford. Ford will then finalize it with Jewell.14 - RFI considerations for new Education Center (John, Frank)
With construction underway, the group decided that progress needs to be carefully monitored. Ford will take the lead on this.15 - Equipment inventory (Jeff)
Still working on it...16 - Deer stand RFI survey (Rick)
Under Fisher's direction, Rosalind is conducting a survey using the Deer Stand. The goal of the survey is to characterize interference over a 24 hour time span. Four 5 MHz bands are monitored over a 24 hour span. The band from 320 to 480 MHz is presently being characterized. Fisher noted that Rosalind is available to do small programming jobs for the IPG.17 - GBT RFI 'harmful levels' document and measurement procedures
The group needs to review and comment on this document.18 - Power line noise monitoring
When the 140-ft. was operational, power line noise monitoring was done about a week before any observations below 500 MHz. This needs to be started again.19 - Measurements of PC/Workstation in a shielded box
Parts have been ordered to characterize interference from a flat screen display.20 - Interference at 1612.17 MHz
This is a holdover from the 140-ft. that needs to be resolved at some point.Initiatives to assemble requirements and specifications in the following areas:
1 - Long term strategy for
response to RFI reports from observers
Quick response to observing problems
Follow-up and feedback to observers
Requirements for detection instrumentation
Telescope operator training and involvement
2 - Measurements and monitoring concerned with NRQZ
3 - RFI environment data base compilations (Rick)
4 - Procedures for acquiring and screening new purchases for RFI compliance
5 - Techniques for designing
or modifying new equipment for RFI compliance
There was a short discussion about whether the IPG should tackle the above issues. It was agreed that they are all worthwhile. It was proposed that a reasonable strategy for attacking these would be for a person could take the lead and compile a straw man as a starting point for group discussion. Acree agreed to take the lead on items 4 and 5.