Green Bank, WV

MEMORANDUM March 23, 1999

TO: R. Fisher, J. Ford, F. Ghigo, R. Lacasse, R. Norrod, M. McKinnon, C. Niday, T. Weadon

FROM: R. Lacasse

SUBJ.: Minutes of Interference Protection Group 03/23/99 Meeting

In attendance: Fisher, Ford, Lacasse, Niday

Minutes of Previous Meeting


Call Outs for Interference


Action Item Review

1 - Technical Seminar on RFI Suppression Requirements and Techniques

First part of seminar, covering the "Why" of RFI suppression, will be given by Fisher tomorrow. The next part, covering the "How", will be given by Niday and Schiebel next week.

2 - Use of Spectral Processor with anechoic chamber

The replacement monitor has been installed.

3 - Site Radio System

Essentially all hardware has been received. Licensing still has to be done. Then some testing with transmitters on the water tower will be done.

4 - Monitor station and anechoic chamber development

Construction of continuum detected power system is in progress. All parts are in and shop work is complete. Assembly and test are imminent.

5 - Microwave Oven Enclosure

A commercial enclosure was purchased ($1500) from EMCOR. Modifications to the enclosure will be made to improve the shielding and make it suitable for an oven enclosure. Delivery is expected in April.

Possibly a bigger problem in the same band are 2.4 GHz video links, commercial products used in transmitting video around households to avoid re-wiring. Niday stated that these are generally spread spectrum, and are Part 15 compliant. They are limited to +30 dbm ERP. Bands from 902 to 928 MHz and around 5.8 GHz are used similarly.

This discussion diverged into a philosophical one. Why should NRAO bother to shield and filter commercial equipment, like microwave ovens, much better than its neighbors? In some cases, our efforts make little or no difference in the noise floor at the telescopes. However, they do set a good example and keep us from being our own worst enemy. Also, they make a statement to visitors, especially those whose must qualify equipment for operation in the Quiet Zone.

6 - Shielded Room Entrances

No progress.

7 - RFI Considerations for new Education Center

No progress.

8 -Harmful Levels Document

Will be handed out at seminar.

9 - Lab RFI Suppression Efforts

No progress.

9 - Use of Interference Reporting System

No comments made.

10 - Interference at 1612.17 MHZ

An L-band antenna with a rotor will soon be mounted atop the 140 ft. and used on maintenance days to monitor this band. The shop is presently building mounting hardware.

11 - RFI Monitor for Education Center

No progress.

12 - Cal and Sig/Ref Switching System for Anechoic Chamber

No progress.

Next Meeting: TBD