RFI Subtraction with a reference horn

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RFI Subtraction with a reference hornF.
Briggs M. Kesteven

• illustrations from Parkes Telescope (Jon Bell et
  al.)
• origins in Int-Mit group at CSIRO ATNF

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gAS
g1I
Rx
Cross Correlation
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R F I
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Reference Antenna
I(t) S ha(t) io(t-ta)
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Reference Antenna
I
I(f) (S Ga(f) e-i2p taf ) Io(f)
G(f) Io(f)
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Cross correlation single polarization feed with
2 reference signals
1. Pol A
G1 G4 Io2
3. Ref 1
G3 G4 Io2
4. Ref 2
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Cross correlation single polarization feed with
2 reference signals
1. Pol A
G1 G4 Io2
C14
3. Ref 1
C34
G3 G4 Io2
4. Ref 2
G1
G1 G4 Io2

G3
G3 G4 Io2
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Practical Application Auto-Correlation
Spectrometer
Power Spectrum P(f)
S
gA2S2
g12 I2
A/C spectrometer
I
g12 I2
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Cross correlation single polarization feed with
2 reference signals
1. Pol A
G1 G3 Io2
C13
G1 G4 Io2
C14
3. Ref 1
C34
G3 G4 Io2
4. Ref 2
C13(f) C14(f) C34(f)
A/C Spectrum Contamination
g12 I2
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Cross correlation dual polarization feed with 2
reference signals
1. Pol A
C13
G1 G3 Io2
2. Pol B
C14
G1 G4 Io2
C23
G2 G3 Io2
C24
G2 G4 Io2
3. Ref 1
C34
G3 G4 Io2
4. Ref 2
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Raw Dynamic Spectra
Time
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Pol A
Pol B
frequency
Canceled Dynamic Spectra
Time
Non-Toxic to celestial signals
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Spectral Domain Contamination the VOLTAGE
spectrum
Estimate g1(f) I(f) X13(f) g3(f) I(f)
Time Domain Contamination
Effectively FIR filter coefficients
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FIR Coefficients
Delay 0.1ms steps

Time 0.1 sec steps
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Pol A
Pol B
using Ref. 3
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Dynamic Pulsar Spectra
Pol. B
Pol. A
Phase
Frequency
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Cancellation Applied
Dynamic Pulsar Spectra
Pol. B
Pol. A
Phase
Frequency
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INTEGRATED PULSE PROFILES
Pulse Phase
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Self-Normalized by Total Power Spectra
Dynamic Pulsar Spectra
Pol. B
Pol. A
Phase
Average Spectra
Frequency
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VLBI
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VLBI
Jodrell Bank
Westerbork
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Power Spectrum at 840 MHz at Jodrell Bank
Cross Correlation Spectrum Jodrell Bank x
Westerbork
1504377
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Celestial Signal
post- correlation processing .
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Conclusions

• complications of multi-path are contained in
• complex gains G(f)
• adaptive filtering with correlation functions
• preserves phase information.
• equivalent to subtraction of the
  voltage waveform