Radio Frequency Interference and How to Deal With It
description
Transcript of Radio Frequency Interference and How to Deal With It
![Page 1: Radio Frequency Interference and How to Deal With It](https://reader036.fdocuments.us/reader036/viewer/2022062723/56813ff1550346895dab0694/html5/thumbnails/1.jpg)
Atacama Large Millimeter/submillimeter ArrayExpanded Very Large Array
Robert C. Byrd Green Bank TelescopeVery Long Baseline Array
Radio Frequency Interference and How to Deal With It
Toney Minter NRAO
![Page 2: Radio Frequency Interference and How to Deal With It](https://reader036.fdocuments.us/reader036/viewer/2022062723/56813ff1550346895dab0694/html5/thumbnails/2.jpg)
2
What can RFI do to your observations?
• Cover your spectral line
![Page 3: Radio Frequency Interference and How to Deal With It](https://reader036.fdocuments.us/reader036/viewer/2022062723/56813ff1550346895dab0694/html5/thumbnails/3.jpg)
3
What can RFI do to your observations?
• Cover your spectral line • Create baseline issues
![Page 4: Radio Frequency Interference and How to Deal With It](https://reader036.fdocuments.us/reader036/viewer/2022062723/56813ff1550346895dab0694/html5/thumbnails/4.jpg)
4
What can RFI do to your observations?
• Cover your spectral line • Create baseline issues• Create non-linear responses
![Page 5: Radio Frequency Interference and How to Deal With It](https://reader036.fdocuments.us/reader036/viewer/2022062723/56813ff1550346895dab0694/html5/thumbnails/5.jpg)
What can you do?
Ignore the RFI Flag data after observations Get worse results than desired Waste lots of telescope time
Modify your observations Try to avoid known RFI Observe when RFI is off (night-time, etc.)
Eliminate the RFI transmitter Not always possible Only have rights in protected bands Quiet Zone Cooperation of transmitter
Cancel RFI signal Need reference antenna Subtract reference antenna signal from data
![Page 6: Radio Frequency Interference and How to Deal With It](https://reader036.fdocuments.us/reader036/viewer/2022062723/56813ff1550346895dab0694/html5/thumbnails/6.jpg)
Planning Your Observations
• There is no magic bullet for dealing with RFI• Understand the RFI
– What frequencies– How strong– How often
• Constant• Periodic• Random
– Signal direction• Look at Spectrum Surveys
– Arecibo• http://www.naic.edu/~rfiuser/smarg-hplots.html
– Green Bank• http://www.gb.nrao.edu/IPG/
![Page 7: Radio Frequency Interference and How to Deal With It](https://reader036.fdocuments.us/reader036/viewer/2022062723/56813ff1550346895dab0694/html5/thumbnails/7.jpg)
Planning Your Observations
• Coordinate the observations if possible– Is RFI less prevalent at night?– Are emitters willing to participate?
• IF system– Set filters and frequencies in IF system to remove RFI
• Use narrow filters• Offset spectral line from bandpass center
– Watch your power levels• Strong RFI can saturate parts of the IF
• Backends– Higher level sampling– Shorter integration times
![Page 8: Radio Frequency Interference and How to Deal With It](https://reader036.fdocuments.us/reader036/viewer/2022062723/56813ff1550346895dab0694/html5/thumbnails/8.jpg)
Ringing from Strong RFI
![Page 9: Radio Frequency Interference and How to Deal With It](https://reader036.fdocuments.us/reader036/viewer/2022062723/56813ff1550346895dab0694/html5/thumbnails/9.jpg)
Removing RFI from Data
• Automated removal of RFI very difficult– Pulsars
• Very short integration time in each sample• Majority of samples do not have “signal”• “Signal” < noise level in sample• Determine noise level• Clip signal well above noise
– Spectral line• Longer integration times
– Fewer samples– Lower noise levels – easier to see RFI
• How do you tell difference between RFI and line?
![Page 10: Radio Frequency Interference and How to Deal With It](https://reader036.fdocuments.us/reader036/viewer/2022062723/56813ff1550346895dab0694/html5/thumbnails/10.jpg)
Flagging Spectral Line Data
• “Types” of RFI– Narrow lines that vary in time– Narrow lines that are persistent
![Page 11: Radio Frequency Interference and How to Deal With It](https://reader036.fdocuments.us/reader036/viewer/2022062723/56813ff1550346895dab0694/html5/thumbnails/11.jpg)
Narrow, Time Varying RFI
![Page 12: Radio Frequency Interference and How to Deal With It](https://reader036.fdocuments.us/reader036/viewer/2022062723/56813ff1550346895dab0694/html5/thumbnails/12.jpg)
Flagging Spectral Line Data
• “Types” of RFI– Narrow lines that vary in time– Narrow lines that are “constant” in time– Strong occasional or periodic RFI
![Page 13: Radio Frequency Interference and How to Deal With It](https://reader036.fdocuments.us/reader036/viewer/2022062723/56813ff1550346895dab0694/html5/thumbnails/13.jpg)
Strong RFI
![Page 14: Radio Frequency Interference and How to Deal With It](https://reader036.fdocuments.us/reader036/viewer/2022062723/56813ff1550346895dab0694/html5/thumbnails/14.jpg)
Flagging Spectral Line Data
• “Types” of RFI– Narrow lines that vary in time– Narrow lines that are “constant” in time– Strong occasional or periodic RFI – Occasional strong out of band RFI
![Page 15: Radio Frequency Interference and How to Deal With It](https://reader036.fdocuments.us/reader036/viewer/2022062723/56813ff1550346895dab0694/html5/thumbnails/15.jpg)
Out of Band RFI
![Page 16: Radio Frequency Interference and How to Deal With It](https://reader036.fdocuments.us/reader036/viewer/2022062723/56813ff1550346895dab0694/html5/thumbnails/16.jpg)
Conclusions
• No Magical solutions• Do your homework before you observe• Do your best to avoid RFI during your observations• Understand your data
– Where is the RFI– When is the RFI
• Flag your data accordingly