1. RFI - How bad is it? - RFI reduction approaches G. Tuccari Istituto di Radioastronomia INAF Bologna - Italy

2. Past experience An extensive monitoring experience has been done in the 2000 within some VLBI EVN stations Reason was monitoring RFI to have a clear picture and get information useful for defining a ‘RFI robust receiver’ The range 50-2000 MHz examined Dedicated instrumentation used to collect a database From that experience it is felt: 1) Site specific actions are necessary because of the substantial difference in the RFI local status 2) Historical information useful for the a-priori protection 3) Both a-priori and current information necessary for good quality observations 4) The worst case UHF observations suggest as RFI protection can make an observation useful more than having to throw away data

3. Next page reports a list of monitoring sites available on the web from CSIRO

4. ParkesParkes Narrabri Mopra VLBI SKA MNRFNarrabriMopraVLBISKAMNRF HomeHome The ATNF News What's On Observers Research Technology Outreach Resources Contact Search Internal The ATNFNewsWhat's OnObserversResearchTechnologyOutreachResourcesContactSearchInternal Monitoring Systems Monitoring IRIDIUM satellite signals near the 1612 MHz OH-Band British Aerospace Australia Spectrum and Frequency Management System (see link under products section)British Aerospace Australia SAT Corporation SETI Australia Serendip Instruments Noto: ICOM IC-9000 communication receiver 100 kHz-2000 MHz, log per antennas for 105-1300 MHz and 1350-2350 MHz Effelsberg: antennas HK014 (100-1300 MHz) and HF902 (1300-3000 MHz) from Rhode & Schwartz Receivers ESMC 20-650 MHz, ESMC-T2 650-1300 MHz, ESMC-FE 1300-3000 MHz from Rhode & Schwartz Jodrell Bank: antennas HK014 and HF902 from Rhode & Schwartz, receiver EB200 from Rhode & Schwartz WSRT: antennas HE202 and HF902 from Rhode & Schwartz, receiver ICOM IC-R9000 Do you have information on monitoring systems that we could link here ? If so, please send the details to Bob SaultBob Sault Last modified: December 17 2002. © Copyright CSIRO Australia 2004. CSIRO Media Release information, Legal Notice and Disclaimer, Privacy Statement.CSIRO Media Release informationLegal Notice and DisclaimerPrivacy Statement

5. What to do? The only way to know how bad it is, it’s cheking it and considering that it is site dependent It is reasonable to expect an RFI presence particularly severe starting from L and S band and gradually reducing its importance (to be verified) Additionally UWB is increasing its presence and importance in a very broad range Better to be not too optimistic, even if in interferometry. A single station very bad contribution could degrade network performance CRAF web site reports useful criteria and information (http://www.astron.nl/craf/ et al.)http://www.astron.nl/craf/

6. Actions 1) knowledge of the site-based systematic RFI in the entire wide band, to be used preliminary and at the time of experiment preparation; 2) in case of severe contribution in some part of the spectrum, protection of the front-end saturation (RFI robust receiver) 3) simultaneous rfi reception with omni-directional antennas for integrated slow rate spectrum recording, to be used at correlation time for avoiding worst case portions of band (you can see this as an extension of the log information); 4) real-time mitigation using fast rate spectrum detection at the back-end; two methods possible: a) worst case bin spectrum removal, b) parallel high data rate fir filters.

7. Knowledge of the site-based RFI Preliminary spectrum analysis If very bad RFI is present somewhere in the spectrum, fixed filters (ex. cryogenic superconducting or cavity filters) Site based ‘fingerprint’ available as correlation mask to remove or reduce portions of data

8. Simultaneous RFI reception Very wide band omni-directional antennas (ex. crossed differential log-periodic) Low cost spectrum analyzer (ex. Aeroflex) Spectra recording, as worst case in log files to be superimposed to the station ‘fingerprint’

9. Real time mitigation Digital Backend able to introduce mitigation at sampled IF level Possible methods adopted for instance in the first DBBC CoreBoard with RFI mitigation firmware: a)Bin removal in the frequency spectrum, about – 20dB b)Notch in Parallel Fir filters, more than 40 dB attenuation

10. DBBC General Schematic View A/D 1 PCI PC FS PC Synthesizer / Distributor H-Maser MK4/VSI max 64 ch CORE HSI HSO PCI Interfaces IFn (MHz) 1~512, 512~1024, 1024~1536, 1536~2048 AGC/ Filter IF 4IF 3IF 2IF 1 A/D 2 A/D 1 A/D 2 HSIR HSOR CORE HSI HSO HSIR HSOR AGC/ Filter AGC/ Filter AGC/ Filter CORE HSI HSO HSIR HSORVSI Interface D/A Monitor The first CoreBoard is performing RFI active mitigation