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%META:TOPICINFO{author="KarenONeil" date="1177585442" format="1.0" version="1.1"}%
%META:TOPICPARENT{name="WebHome"}%
RFI
Unlike other telescopes which use dynamic scheduling, the GBT is in the unique position of going to extremely low frequencies where RFI can be a real problem. The RFI management group at Green Bank has worked hard to clean up the RFI environment. Part of this work has included getting formal and informal agreements between other users of the GBT's observing band, including military use and use by amateur radio users. Dynamic scheduling needs to recognize this work and capitalize on it. Information on how we will deal with RFI can be found on the RFI planning page
To do this, we propose the following:
- All known RFI will be listed in an easily readable format for observers to look at before writing their proposals, so that proposals are not written to observe in cases where RFI is known to be a problem and cannot be mitigated.
- To facilitate cooperation with groups with whom we do not have a formal agreement, but whom are willing to limit emissions at certain frequencies when it is possible for them to do so, the output from the Dynamic Scheduling Software (DSS) will be displayed on a public website, and will include the frequency ranges of every scheduled project (in GHz). This requirement needs to be modified once we have a reasonable idea of the predictability of weather for the GBT and know if it is feasible to write a semi-accurate telescope schedule and, if it is possible, how far in advance this schedule can be written. At a minimum, we should be able to post a schedule of the prime focus and other feed changes, at least within a few days. At best we may have a rough schedule that can be seen by all other users of the spectrum.
- The Dynamic Scheduling Software (DSS) needs an easy means to mark unexpected RFI problems. This needs to be a database which can both be changed on the fly (e.g. when RFI is seen or remedied) and which also can have dates, times, and frequency entered into it. If a project is begun and then canceled due to unexpected RFI, that fact, along with all critical parameters needed to define the RFI, will be both logged into the operator's log and e-mailed to the RFI group.
- If RFI is present in an observing band, we need two different types of indicators. The first would indicate that a project has been negatively affected by the RFI and the observer wishes not to try and run the project until the RFI has been mitigated. The second is simply a warning that there is known RFI in that band and that observers of the band need to be warned of its presence.
- When RFI is seen by the observers, the GBT telescope operators need to be able to readily look at the GBT RFI monitoring system (to be deployed before dynamic scheduling begins). If the RFI can also be seen on the monitor, that fact should be noted also in the Dynamic Scheduling Software (DSS). When the RFI is then no longer seen on the monitor, the frequency should be unmarked as existing (but will remain in the RFI database for reference later). If the RFI cannot be seen on the monitor, the telescope operators will wait for word from either a member of the RFI group or one of the staff support scientists before unblocking the frequency in the DSS database.
- In the cases where we have full cooperation with an individual or group (e.g. amateur radio beacons), and that group cannot easily turn off its signal with only 30 minutes notice, we need to do the following:
- Have an easy to understand (and update) list of all frequencies, times signatures, and power levels, of signals for which we have full cooperation;
- Have a ready means for the observer to tell us that he needs coordination with a given frequency(s). This would best be done through a tool which feeds that fact directly to the Dynamic Scheduling Software (DSS) (e.g. a query in the Proposal Submission Tool);
- Once the need for coordination is registered with the database, the RFI/EMI group (rfigrp) will be added to all scheduling e-mails for that project
- When the project moves to high on its probability list, its parameters will change and it will become a Fixed Window project, with a three day window, and the RFI group will notify the person(s) responsible for the interfering signal about the schedule
- The person(s) responsible for the interfering signal will be asked to check the current GBT schedule before turning on the signal during the Fixed Window.
- In the cases where we have full cooperation with an individual or group and that group can easily turn off the signal with only 30 minutes notice, we need to do the following:
- Have an easy to understand (and update) list of all frequencies, times signatures, and power levels, of signals for which we have full cooperation;
- Have a ready means for the observer to tell us that he needs coordination with a given frequency(s). This would best be done through a tool which feeds that fact directly to the Dynamic Scheduling Software (DSS) (e.g. a query in the PST);
- Once the need for coordination is registered with the database, the RFI/EMI group (rfigrp) will be added to all scheduling e-mails for that project
- When the project is selected by the telescope operator, the operator will see an indicator noting that he or she will need to call the person responsible for the transmitter and request that he or she turn the transmitter off for the upcoming TP. The observer should be contacted before the person responsible for the transmitter to ensure the observer is indeed available for observing.
Note that the presence of the database for noting RFI could likely turn into a great tool for understanding the RFI at Green Bank and for building up a history of the RFI.
-- KarenONeil - 26 Apr 2007 |