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

 easily reaches 80+ dB above natural noise levels. 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.
 \secc Bandwidth
-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 wideband 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.
+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.
 \sec Current status of receivers digitalization units
 % dopsat navaznost na aktualne pouzivane digitalizacni jednotky
 Only few digitalization systems dedicated for radioastronomy currently exists.  Currently existing systems uses either custom design of whole receiver or they are constructed from commercially available components. Open-source principle attempts are very rare in radioastronomy field.
-\secc Coustom digitalization system
+\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 instrument developed in one piece with leads to 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. \url{http://arxiv.org/abs/1305.3550}
-Coustom 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.
-The system requires proper handling of huge amounts of data.
-Professional astronomers use proprietary digitalization units \url{http://arxiv.org/abs/1305.3550} or by multichannel sound cadrd on amateur levels \url{http://fringes.org/}
 This price is comparable with value of one ADC channel in our design described in following part of document.
 Mudular radioastronomy hardware: https://casper.berkeley.edu/papers/200509URSI.pdf
+In opposite of professional astronomers which uses proprietary digitalization units, amateur radioastronomers currently uses multichannel sound cards \url{http://fringes.org/}
+It is evident that current radioastronomy lacks of proper hardware which could be used on both communities professionals and amateurs. In addition open-source hardware

Subversion Repositories svnkaklik

(root)/dokumenty/skolni/diplomka/introduction.tex @ 1156 – Rev 1106 → 1107