NATIONAL RADIO ASTRONOMY OBSERVATORY
Green Bank, WV
MEMORANDUM
July 27, 1999
TO: R. Fisher, J. Ford, F. Ghigo, R. Lacasse, C. Niday, T. Weadon
FROM: R. Lacasse
SUBJ.: Minutes of Interference Protection Group 07/27/99 Meeting
In attendance: Ghigo, Fisher, Ford, Lacasse, Weadon
Minutes of Previous Meeting
Approved.
Call Outs for Interference
None.
Action Item Review
1. IAU Symposium
of Light Pollution and RFI .
This symposium generated a letter to observatory directors requesting
that they comply with the standards that radio astronomy requests of others.
Fisher reported that he has been selected to write a chapter on RFI
measurement techniques for the ITU Radio Astronomy handbook.
Another meeting, concentrating on measurements and standards will
be held next year in Manchester, England.
2. Emissions from
new diesel vehicles.
New diesel vehicles acquired by the site include quite a bit of electronics
and thus may be a source of RFI. A decision was made to measure one
of the vehicles. Since it cannot be brought into the anechoic chamber,
sensitive measurements will be difficult. A decision was made to
attempt a difference measurement (truck on/ truck off) near the anechoic
chamber.
3. GBT RFI 'harmful levels'
document (Rick)
The priority of this task has been raised by item 1 above.
4. Blanking and sig/ref
switching system system for anechoic chamber (Rich, Chuck, Rick)
No progress on adding blanking to the continuum detector system.
However, for measurements that need to be made in the near future, the
blanking feature is not required. Its implementation can be postponed.
A system to switch AC power on and off for the Quadrant Detector Laser
Supply and Feed Defroster, without generating its own RFI, is required
ASAP. Weadon and Lacasse will look into this.
5. Site radio system (Chuck)
The power combiner has been received and tested. A meeting has
been scheduled to discuss the installation of an antenna on the water tower.
6. Microwave oven in shielded
test box (John)
The box has been repaired at the factory and was shipped back to NRAO
last Friday.
7. Shielded room entrances
(John, Rick)
8. Monitor station and anechoic chamber
developments (Rick, Rich)
The stand is complete. Cables have been pulled. A box for
electronics has been installed at the base of the stand.
9. Progress on suppressing
RFI from equipment that has been measured in the anechoic chamber
A summary spreadsheet, listing required shielding for various devices,
has been provided to Ford. It was recommended that a few columns
be added to the sheet to specify the attenuation of the room which houses
the device and the resulting additional shielding required of the device
itself.
No progress on other items
on action item list.
Next Meeting: August 10, 0800.