WebSVN – svnkaklik – Diff – /dokumenty/skolni/diplomka/introduction.tex



 
The novel approach of receiver construction described above goes hand-in-hand with new requirements on receiver parameters as well. Currently no additional attempts to improve the signal-to-noise ratio on single antenna are performed. There are however other parameters requested nowadays. 
 
\secc Sensitivity and noise number
 
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.  
 
\secc Dynamic range
 
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. 
The maximal theoretical dynamic range of ADC could be estimated from ADC bit depth using a following formula  \ref[dynamic-range]
 
\label[dynamic-range]
$$D.R. [dB] = 20 \cdot \log(2^n) $$
 
The formula \ref[dynamic-range] gives values shown in table  below \ref[ADC-dynamic-range].
 
\midinsert \clabel[ADC-dynamic-range]{Dynamic range versus bit depth}
\ctable{cc}{

\secc Custom digitalization system
 
Custom designs usually uses non-recurring engineering  for development specific solution for observation project thus costs of this instruments are very high if developed instrument are not reproduced many times. Typical example of instrument developed and manufactured in one piece with enormous founding resources draws is Arecibo ALFA survey multi beam feed Array. 
Another opposite example for custom receiver and digitalization unit design is LOFAR system developed by Astron in Netherlands \cite[lofar].
 
LOFAR is innovative radioastronomy system which uses the phased antenna array approach in enormous scale and thousands (around $2 \cdot 10^4$) of antennas are manufactured an deployed on field. The centrer of LOFAR system is situated in Netherlands and peripheral antennas and connection network are extended to other European countries. 
 
LOFAR project must use low cost hardware due to systems scale. Special construction techniques are used to keep overall project budget at acceptable levels (specially designed polystyrene supporting blocks for HBA antennas for example). Many of used components are manufactured in mass scale for other than scientific use LBA antennas masts are made from standard PVC plastic waste pipes and LOFAR uses low cost direct sampling receiver. Whole project has been designed by Netherlands Institute for Radio Astronomy, which produces many similarly sophisticated devices\cite[astron-devices]. 
 
\secc Modular digitalization systems
 

Subversion Repositories svnkaklik

(root)/dokumenty/skolni/diplomka/introduction.tex – Rev 1111 → 1116

Rev 1111		Rev 1116
Line 44...		Line 44...
44		44
45	`The novel approach of receiver construction described above goes hand-in-hand with new requirements on receiver parameters as well. Currently no additional attempts to improve the signal-to-noise ratio on single antenna are performed. There are however other parameters requested nowadays.`	45	`The novel approach of receiver construction described above goes hand-in-hand with new requirements on receiver parameters as well. Currently no additional attempts to improve the signal-to-noise ratio on single antenna are performed. There are however other parameters requested nowadays.`
46		46
47	`\secc Sensitivity and noise number`	47	`\secc Sensitivity and noise number`
48		48
49	`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.`	49	`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.`
50		50
51	`\secc Dynamic range`	51	`\secc Dynamic range`
52		52
53	`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.`	53	`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.`
54	`The maximal theoretical dynamic range of ADC could be estimated from ADC bit depth using a following formula \ref[dynamic-range]`	54	`The maximal theoretical dynamic range of ADC could be estimated from ADC bit depth using a following formula \ref[dynamic-range]`
55		55
56	`\label[dynamic-range]`	56	`\label[dynamic-range]`
57	`$$ D.R. (dB) = 20 * log(2^n) $$`	57	`$$D.R. [dB] = 20 \cdot \log(2^n) $$`
58		58
59	`The formula \ref[dynamic-range] gives values shown in table below \ref[ADC-dynamic-range].`	59	`The formula \ref[dynamic-range] gives values shown in table below \ref[ADC-dynamic-range].`
60		60
61	`\midinsert \clabel[ADC-dynamic-range]{Dynamic range versus bit depth}`	61	`\midinsert \clabel[ADC-dynamic-range]{Dynamic range versus bit depth}`
62	`\ctable{cc}{`	62	`\ctable{cc}{`
Line 88...		Line 88...
88	`\secc Custom digitalization system`	88	`\secc Custom digitalization system`
89		89
90	`Custom designs usually uses non-recurring engineering for development specific solution for observation project thus costs of this instruments are very high if developed instrument are not reproduced many times. Typical example of instrument developed and manufactured in one piece with enormous founding resources draws is Arecibo ALFA survey multi beam feed Array.`	90	`Custom designs usually uses non-recurring engineering for development specific solution for observation project thus costs of this instruments are very high if developed instrument are not reproduced many times. Typical example of instrument developed and manufactured in one piece with enormous founding resources draws is Arecibo ALFA survey multi beam feed Array.`
91	`Another opposite example for custom receiver and digitalization unit design is LOFAR system developed by Astron in Netherlands \cite[lofar].`	91	`Another opposite example for custom receiver and digitalization unit design is LOFAR system developed by Astron in Netherlands \cite[lofar].`
92		92
93	`LOFAR is innovative radioastronomy system which uses the phased antenna array approach in enormous scale and thousands (around $2*10^4$) of antennas are manufactured an deployed on field. The centrer of LOFAR system is situated in Netherlands and peripheral antennas and connection network are extended to other European countries.`	93	`LOFAR is innovative radioastronomy system which uses the phased antenna array approach in enormous scale and thousands (around $2 \cdot 10^4$) of antennas are manufactured an deployed on field. The centrer of LOFAR system is situated in Netherlands and peripheral antennas and connection network are extended to other European countries.`
94		94
95	LOFAR project must use low cost hardware due to systems scale. Special construction techniques are used to keep overall project budget at acceptable levels (specially designed polystyrene supporting blocks for HBA antennas for example). Many of used components are manufactured in mass scale for other than scientific use LBA antennas masts are made from standard PVC plastic waste pipes and LOFAR uses low cost direct sampling receiver. Whole project has been designed by Netherlands Institute for Radio Astronomy, which produces many similarly sophisticated devices\cite[astron-devices].	95	LOFAR project must use low cost hardware due to systems scale. Special construction techniques are used to keep overall project budget at acceptable levels (specially designed polystyrene supporting blocks for HBA antennas for example). Many of used components are manufactured in mass scale for other than scientific use LBA antennas masts are made from standard PVC plastic waste pipes and LOFAR uses low cost direct sampling receiver. Whole project has been designed by Netherlands Institute for Radio Astronomy, which produces many similarly sophisticated devices\cite[astron-devices].
96		96
97	`\secc Modular digitalization systems`	97	`\secc Modular digitalization systems`
98		98