Transcript RFI - How bad is it? - RFI reduction approaches

RFI
- How bad is it?
- RFI reduction approaches
G. Tuccari
Istituto di Radioastronomia INAF
Bologna - Italy
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
Next page reports a list of monitoring sites
available on the web from CSIRO
Parkes Narrabri Mopra VLBI SKA MNRF
Home The ATNF News What's On Observers Research Technology Outreach Resources Contact Search Internal
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)
• 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 Sault
Last modified: December 17 2002.
© Copyright CSIRO Australia 2004. CSIRO Media Release information, Legal Notice and Disclaimer, Privacy Statement.
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.)
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.
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
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’
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
DBBC General Schematic View
IFn (MHz)
1~512, 512~1024,
1024~1536, 1536~2048
IF 1
IF 2
IF 3
IF 4
AGC/
Filter
AGC/
Filter
AGC/
Filter
AGC/
Filter
A/D 1
A/D 2
A/D 1
A/D 2
HSI
HSIR
CORE
H-Maser
FS PC
Synthesizer / Distributor
PCI
PC
HSO
HSOR
HSI
HSIR
CORE
HSO
PCI
Interfaces
The first
CoreBoard is
performing RFI
active mitigation
HSOR
HSI
HSIR
CORE
HSO
HSOR
VSI
Interface
D/A
Monitor
MK4/VSI
max
64 ch