Green Bank, WV

MEMORANDUM February 9, 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 02/09/99 Meeting

In attendance: Fisher, Ford, Lacasse, Niday

Minutes of Previous Meeting


Call Outs for Interference


Committee Membership

Because of many other responsibilities, McKinnon and Ghigo will attend on an "as needed" basis.

Action Item Review

1 - Tourists Digital Cameras

Our goal is to minimize interference at the telescopes. A prime offender is digital cameras, but many other devices can also cause problems. Because of the open nature of the site and tour program it is difficult to mandate compliance to any policy we might try to establish. Encouraging the public to cooperate in minimizing interference may be possible. One approach might be to make some sort of RFI monitor for the tour center. Devices could be scanned by the monitor and some sort of simple measure of the devices' RFI could be displayed (audio, analog meter ??).

2 - Interference at 1612.17 MHz

We received a request for an update on interference at 1612.17MHz. This signal is still unidentified. Fisher noted that L-band monitoring capability may be up in about 6 weeks, so we can hope to make progress on this item then. Lockman also stated (via e-mail) that he would use some of his 140' time to try to identify the signal.

3 - GBT Subreflector Actuator Heaters

Both COMSAT and NRAO have come up with the same alternative to the microprocessor controlled heaters for the GBT subreflector actuators: heat tape. This consists of wires embedded in a material which is varies its resistance as a function of temperature. These heaters look like an extension cord and are self-regulating. Temperature control is not as tight as the microprocessor controlled system, but this is not really an issue for this system. The heat tape can be purchased with an overall shield for safety purposes; it could also be used for RFI shielding with minor modification.

A 6' sample of this heat tape was tested in the anechoic chamber. No RFI was detected from 100 to 1000 MHz, using amplifiers and the spectrum analyzers as a backend.

System tests are imminent. For now this item can be dropped from the IPG's action item list.

4 - Site Radio System

All the components for the system have been ordered. The portables (8) have been received. Repeaters have a 12 to 16 week delivery (ordered early Jan.).

The system has been evaluated by the Quiet Zone administrator, Wes Sizemore. An ERP of 0.1 W from the reflector site, or 0.2 W from the water tower is allowed.

The licensing of the system with the FCC is incomplete.

5 - Microwave Oven Enclosure

Commercial enclosures would cost in the neighborhood of $5K. We have decided to just improve the door on our existing box. Telescope operations has requested that this be a high priority. (The operators are getting hungry!)

6 - Technical Seminar on RFI Suppression

Fisher will try to put this together in a few weeks.

7 - Monitor Station and Anechoic Chamber Developments

A site, for the platform for the monitor station, just west of the 45' telescope, has been selected and surveyed. An L-band system to be mounted near the 140' focus will be ready in about 6 wks.

8 - Education Center

No progress.

9 - FCC Class B requirements and test procedures

No progress.

10 - Lab RFI suppression efforts

No progress

11 - Cal and Sig/Ref Switching System for the Anechoic Chamber

No progress.

12 - GBT RFI "Harmful Levels" Document

On hold.

13 - Use of Spectral Processor with the Anechoic Chamber

The program Exceed has been installed and tested. Fisher will do a system test when he has time.

Next Meeting: Feb. 23, 1999, at 0800