Geophysical interpretation of the magnetic anomaly at Marmora, Ontario, 31 c/5

Bower, M E

doi:10.4095/101239

Cited by 2 publications

(4 citation statements)

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“…To remain general the G-terms are kept as complex quantities, to allow for any effects on the phase that are not due to the geometric delay. It is assumed that there is only one interfering signal in a frequency channel (see Bower 2001 for a discussion of multiple interferers), and that there is negligible reference antenna gain in the direction of S, i.e., reference antennae do not measure signal from astronomical sources. These are important assumptions, but often quite reasonable (the latter assumption is strengthened because the weak astronomy signal enters the reference antennae through side-lobes).…”

Section: The Modelmentioning

confidence: 99%

“…Also, since the reference signal is being scaled in an attempt to match its own RFI to the RFI in the main signal, the larger G r is relative to G m (for example using a reference antenna that is pointing directly at the interfering source), the smaller the scaling factor (weighting amplitude) and thus the amount of injected receiver noise. When INR r ≫ 1 and G r ≫ G m both of the residual terms drop off and extremely good results are achieved (Barnbaum & Bradley 1998;Bower 2001).…”

Section: Mk1: Single Reference Adaptive Cancellersmentioning

confidence: 99%

“…In radio astronomy, real-time adaptive filters can be used to modify an auxiliary voltage time series (the reference signal) so that it cancels RFI from an astronomical voltage time series (Barnbaum & Bradley 1998;Bower 2001;Mitchell & Robertson 2005). For each voltage sample the filters are allowed to slightly vary their internal coefficients in order to adapt to any changes taking place in the RFI.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Alternative Adaptive Filter Structures for Improved Radio Frequency Interference Cancellation in Radio Astronomy

Mitchell¹,

Robertson²,

Sault³

2005

Astron J

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In radio astronomy, reference signals from auxiliary antennae, receiving only the radio frequency interference (RFI), can be modified to model the RFI environment at the astronomy receivers. The RFI can then be cancelled from the astronomy signal paths. However, astronomers typically only require signal statistics. If the RFI statistics are changing slowly, the cancellation can be applied to the signal correlations at a much lower rate than required for standard adaptive filters. In this paper we describe five canceller setups; pre-and postcorrelation cancellers that use one or two reference signals in different ways. The theoretical residual RFI and added noise levels are examined, and demonstrated using microwave television RFI at the Australia Telescope Compact Array. The RFI is attenuated to below the system noise, a reduction of at least 20 dB. While dualreference cancellers add more reference noise than single-reference cancellers, this noise is zero-mean and only adds to the system noise, decreasing the sensitivity. The residual RFI that remains in the output of singlereference cancellers (but not dual-reference cancellers) sets a non-zero noise floor that does not act like random system noise and may limit the achievable sensitivity. Thus dual-reference cancellers often result in superior cancellation. Dual-reference pre-correlation cancellers require a double-canceller setup to be useful and to give equivalent results to dual-reference post-correlation cancellers.

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Section: The Modelmentioning

confidence: 99%

Section: Mk1: Single Reference Adaptive Cancellersmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Alternative Adaptive Filter Structures for Improved Radio Frequency Interference Cancellation in Radio Astronomy

Mitchell¹,

Robertson²,

Sault³

2005

Astron J

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“…Bower (2005) discusses the theory of using AIC with telescope arrays. Laboratory and field tests have demonstrated that the technique can effectively cancel interferers (e.g., Bower 2001). AIC has an advantage over other techniques, in that it makes no assumption about the frequency-or time-domain characteristics of the RFI.…”

Section: Introductionmentioning

confidence: 99%

Comparison of Radio-Frequency Interference Mitigation Strategies for Dispersed Pulse Detection

Hogden

Wiel

Bower

et al. 2012

ApJ

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Impulsive radio-frequency signals from astronomical sources are dispersed by the frequency dependent index of refraction of the interstellar media and so appear as chirped signals when they reach earth. Searches for dispersed impulses have been limited by false detections due to radio frequency interference (RFI) and, in some cases, artifacts of the instrumentation. Many authors have discussed techniques to excise or mitigate RFI in searches for fast transients, but comparisons between different approaches are lacking. This work develops RFI mitigation techniques for use in searches for dispersed pulses, employing data recorded in a "Fly's Eye" mode of the Allen Telescope Array as a test case. We gauge the performance of several RFI mitigation techniques by adding dispersed signals to data containing RFI and comparing false alarm rates at the observed signal-to-noise ratios of the added signals. We find that Huber filtering is most effective at removing broadband interferers, while frequency centering is most effective at removing narrow frequency interferers. Neither of these methods is effective over a broad range of interferers. A method that combines Huber filtering and adaptive interference cancellation provides the lowest number of false positives over the interferers considered here. The methods developed here have application to other searches for dispersed pulses in incoherent spectra, especially those involving multiple beam systems.

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Geophysical interpretation of the magnetic anomaly at Marmora, Ontario, 31 c/5

Cited by 2 publications

References 0 publications

Alternative Adaptive Filter Structures for Improved Radio Frequency Interference Cancellation in Radio Astronomy

Alternative Adaptive Filter Structures for Improved Radio Frequency Interference Cancellation in Radio Astronomy

Comparison of Radio-Frequency Interference Mitigation Strategies for Dispersed Pulse Detection

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