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\secc Sensitivity and noise number
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\secc Sensitivity and noise number
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Sensitivity and noise number are parameters that are tied together, but multi antenna and multi-receiver arrays force the price of receiver to be kept at minimal value. This implies that the sensitivity and noise number have to be at least so good in the detection (signal $/$ noise $>$ 1 ) of an observed object, that it would be detected on the majority of receivers connected to an observation network.
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Sensitivity and noise number are parameters that are tied together, but multi antenna and multi-receiver arrays force the price of receiver to be kept at minimal value. This implies that the sensitivity and noise number have to be at least so good in the detection (signal $/$ noise $>$ 1 ) of an observed object, that it would be detected on the majority of receivers connected to an observation network.
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\secc Dynamic range
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\secc Dynamic range
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\label[dynamic-range-theory]
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Dynamic range represents a huge problem of current radioastronomical receivers. This parameter is enforced by everywhere present humans made EMI radiation on RF frequencies. The modern radio astronomy receiver must not be saturated by this high levels of signals but still needs to have enough sensitivity to see faint signals from natural sources. Dynamic range is limited either by the construction of analogue circuitry in receiver or by the digitalisation unit.
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Dynamic range represents a huge problem of current radioastronomical receivers. This parameter is enforced by everywhere present humans made EMI radiation on RF frequencies. The modern radio astronomy receiver must not be saturated by this high levels of signals but still needs to have enough sensitivity to see faint signals from natural sources. Dynamic range is limited either by the construction of analogue circuitry in receiver or by the digitalisation unit.
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The maximal theoretical dynamic range of ADC could be estimated from ADC bit depth using a following formula \ref[dynamic-range]
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The maximal theoretical dynamic range of ADC could be estimated from ADC bit depth using a following formula \ref[dynamic-range]
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\label[dynamic-range]
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\label[dynamic-range]
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16 & 96 \cr
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16 & 96 \cr
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24 & 144 \cr
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24 & 144 \cr
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}
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}
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\caption/t Standard bit depths of ADC and its theoretical dynamic range.
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\caption/t Standard bit depths of ADC and its theoretical dynamic range.
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\endinsert
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\endinsert
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% dopsat cast o minimalnim dynamickem rozsahu ADC.
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If we look at actual spectrum occupancy in Europe (measured in power spectral density) we see that signal dynamic range in spectra
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If we look at actual spectrum occupancy in Europe (measured in power spectral density) we see that signal dynamic range in spectra
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easily reaches more than 80 dB above natural noise levels \cite[spectrum-observatory]. If we don't want to deal with receiver saturation or poor sensitivity we need a receiver and digitalization unit which has comparable dynamical range of with received signals. This imply use of least 14 bit ADC without any spare of range.
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easily reaches more than 80 dB above natural noise levels \cite[spectrum-observatory]. If we don't want to deal with receiver saturation or poor sensitivity we need a receiver and digitalization unit which has comparable dynamical range of with received signals. This imply use of least 14 bit ADC without any spare of range. But 16 bit range should be optimal as we have spare range for strongest RF signals. Two bytes sample range has in addition a good efficiency in use standard power of 2 data types length. We lock for use 16bit digital range as optimal for our design.
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\secc Bandwidth
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\secc Bandwidth
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Historically, the parameter of bandwidth in radioastronomical receiver used to be within the kilohertz range. Small bandwidth was acceptable because observations were processed directly by listening or by paper chart intensity recorder. Chart recorder integrated energy of signal over defined small bandwidth which was suitable for detecting the intensity variance of microwave background. No wide-band transmitters existed in that era (except for TV transmitters) and tuning to other neighbouring frequency was easy as they were mostly vacant. Parallel observations from several places were unnecessary as well because the electromagnetic conditions were nearly same at all locations.
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Historically, the parameter of bandwidth in radioastronomical receiver used to be within the kilohertz range. Small bandwidth was acceptable because observations were processed directly by listening or by paper chart intensity recorder. Chart recorder integrated energy of signal over defined small bandwidth which was suitable for detecting the intensity variance of microwave background. No wide-band transmitters existed in that era (except for TV transmitters) and tuning to other neighbouring frequency was easy as they were mostly vacant. Parallel observations from several places were unnecessary as well because the electromagnetic conditions were nearly same at all locations.
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