/Designs/Radio_meteor_detector/DOC/SRC/radio_meteor_detector.en.tex
49,7 → 49,7
\newpage
\section{Introduction}
 
The detection of meteors by radio is most readily accomplished by a method known as "forward scatter". This technique usually exploits the existence of a VHF radio transmitter intended for some other purpose (such as historically analog radio or TV broadcasting) and which is preferably situated some way beyond the optical horizon so that the direct signal does not desensitise the receiving equipment. The radio signal reflects mainly from the ionised meteor trail as it forms and dissipates, causing a brief signal to be heard on or close to the transmitter frequency. The trails form in the ionosphere (i.e., the upper atmosphere) at a height of about 100 $\pm$ 20 km.
The detection of meteors by radio is most readily accomplished by a method known as "forward scatter". This technique usually exploits the existence of a VHF radio transmitter intended for some other purpose (such as historically analogue radio or TV broadcasting) and which is preferably situated some way beyond the optical horizon so that the direct signal does not desensitise the receiving equipment. The radio signal reflects mainly from the ionised meteor trail as it forms and dissipates, causing a brief signal to be heard on or close to the transmitter frequency. The trails form in the ionosphere (i.e., the upper atmosphere) at a height of about 100 $\pm$ 20 km.
 
Direct reflection from the meteoroid itself is not so readily detected. Meteoroids are not necessarily reflective at radio frequencies, they are usually small (0.05 - 200mm) and they generally enter the ionosphere at supersonic velocities. Thus the direct signal is usually weak; and the initial Doppler shift is large, making it difficult to associate the signal with the transmitter. Sometimes however, a Doppler shifted signal is observed to slew onto or across the transmitter frequency at the beginning of the detection event. This is the reflection from the ball of plasma surrounding the meteoroid (as opposed to the trail left behind), and is known as the "head echo".
 
59,7 → 59,7
 
\section{Description of construction}
 
This construction of radio meteor detector uses France GRAVES space-surveillance radar. Which has transmitting power of several megawatts at frequency 143.05 MHz.
This construction of radio meteor detector uses France GRAVES space-surveillance radar. The radar has transmitting power of several megawatts at frequency 143.05 MHz.
 
\subsection{Antenna}
The detector station usually uses modified ground plane antenna. Adjusted in angle of 30$^\circ$ to East this configuration seems to be optimal to detecting stations in the Czech Republic.
68,6 → 68,7
\begin{center}
\includegraphics [width=80mm] {./img/GP143MHz.JPG}
\end{center}
\caption{Antenna used at detection station}
\end{figure}
 
The received signal from antenna is amplified by specially constructed LNA. This step is needed for feeding the signal trough relative long (several metres) coax RG58. Construction of LNA01A is described on MLAB project site.
80,19 → 81,21
\begin{center}
\includegraphics [width=80mm] {./img/meteor-detector_receiver.JPG}
\end{center}
\caption{Example of meteor detector receiver setup}
\end{figure}
 
 
\begin{figure} [htbp]
\begin{center}
\includegraphics [width=120mm] {./img/zakladni_schema.png}
\includegraphics [width=150mm] {./img/zakladni_schema.png}
\end{center}
\caption{Schematic drawing of complete meteor detector}
\end{figure}
 
 
\subsection{Time synchronisation}
 
Time synchronisation has crucial importance in any modern science measurement. There is possibility of using many synchronisation techniques. Such as NTP od GPS (see for our article at for our experiences)
Time synchronisation has crucial importance in any modern science measurement. There is possibility of using many synchronisation techniques. Such as NTP or GPS (see for our article at for our experiences)
 
Suggested method for time synchronisation of a measuring station depends on level of desired information which would be obtained from meteor reflection event.
 
100,23 → 103,29
 
\begin{figure}[htbp]
\begin{center}
\includegraphics [height=80mm] {./img/colorgram.png}
\includegraphics [width=150mm] {./img/colorgram.png}
\end{center}
\end{figure}
\caption{Example of measured hourly count of meteor showers}
\end{figure}
 
\section{Software setup}
 
For simple PC based monitor station we are using SpectrumLab software with our configuration and detection script.
 
Local oscillator of SDRX01B - usually CLKGEN01B with tunning controller PIC18F455001A can be set up from PC or can be programmed for fixed start up frequency. If fixed start up frequency is correctly saved the only step for tunning the LO is provide power trought USB cable from PC and then press the RESET button of tunning microcontroler module. After that the LO shout be tuned on saved start up frequency. This frequency can be changed by
Local oscillator of SDRX01B - usually CLKGEN01B with tuning controller PIC18F455001A can be set up from PC or can be programmed for fixed start up frequency. If fixed start up frequency is correctly saved the only step for tuning the LO is provide power trough USB cable from PC and then press the RESET button of tuning microcomputer module. After that the LO shout be tuned on saved start up frequency. This frequency can be changed by
 
\begin{thebibliography}{99}
\bibitem{DR2G}{Spectrum Lab}
\href{http://www.qsl.net/dl4yhf/spectra1.html}{http://www.qsl.net/dl4yhf/spectra1.html}
 
http://www.gb2nlo.org/index.php/articles/meteordet
http://www.amsmeteors.org/richardson/distance.html
\bibitem{DR2G}{Radio Meteor Detection}
\href{http://www.gb2nlo.org/index.php/articles/meteordet}{http://www.gb2nlo.org/index.php/articles/meteordet}
 
\bibitem{DR2G}{Meteor distance parameters}
\href{http://www.amsmeteors.org/richardson/distance.html}{http://www.amsmeteors.org/richardson/distance.html}
 
 
 
 
\end{thebibliography}
\end{document}