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— | en:rmds [2013/07/01 13:25] – [Signal digitalization] fluktuacia | ||
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+ | ====== Radio Meteor Detector Station RMDS01A ====== | ||
+ | |||
+ | RMDS01A device is the basic SDR receiver set for radio detection of meteor trails. Compared to other methods, its main advantage is in fact, that it uses software-defined receiver, that enables various advanced signal processing techniques. | ||
+ | |||
+ | ====== Meteor detection using GRAVES radar ====== | ||
+ | |||
+ | The advantages of using signal from military GRAVES radar, compared with the conventional observations using TV transmitters, | ||
+ | |||
+ | ===== Hardware Configuarion of detection station ===== | ||
+ | |||
+ | Most of the used components come from [[http:// | ||
+ | |||
+ | ==== Necessary equipment ==== | ||
+ | |||
+ | - Receiver [[en: | ||
+ | - [[http:// | ||
+ | - 2x power module [[en: | ||
+ | - 2x Power Supplies 12V [[http:// | ||
+ | - Coaxial cable RG58 [[http:// | ||
+ | - Preamplifier [[en: | ||
+ | - 3x SMA cable connector [[http:// | ||
+ | - UHF connector - panel socket and cable jack (for antenna construction). | ||
+ | - PC with computing capabilities for signal processing. Tested minimum for 48kHz sampling is Intel Atom N270 1.6GHz 1GB RAM. | ||
+ | - Audio interface [[http:// | ||
+ | - Internet connectivity | ||
+ | |||
+ | |||
+ | ==== Receiver antenna ==== | ||
+ | |||
+ | === 1/4 Ground Plane === | ||
+ | |||
+ | This is the most basic antenna for receiving the signal reflected from ionized trails. It has an advantage in having a small size, so it can be installed on balcony, terrace etc. Its simple construction enables easy assembly and this makes it particularly suitable for beginners. | ||
+ | |||
+ | The main drawback is the emitting characteristic, | ||
+ | |||
+ | [[http:// | ||
+ | |||
+ | Antena Lead connector is [[http:// | ||
+ | Coax connector is [[http:// | ||
+ | |||
+ | === Other antenna types === | ||
+ | |||
+ | An interesting antenna construction, | ||
+ | |||
+ | |||
+ | Other interesting experiment could include the use of two crossed dipoles over conducting plane. This would probably enable the integration of amplifier directly into the antenna and the creation of the active antenna with better noise parameters and reliability than separated assembly of GP antenna and LNA. | ||
+ | |||
+ | The [[http:// | ||
+ | |||
+ | ==== Preamplifier LNA01A ==== | ||
+ | |||
+ | High quality preamplifier is necessary to operate with 1/4 Ground Plane type of antenna due to low gain and low intensities of reflected signal. | ||
+ | |||
+ | [[http:// | ||
+ | |||
+ | ==== Coaxial connectors ==== | ||
+ | |||
+ | Optimal to use are MLAB standard screw coaxial cable connectors of SMA type that are more durable and have better electrical characteristics that other connector types (like BNC, F). | ||
+ | |||
+ | It is not recommended to use BNC connectors due to their low resistance against bad weather conditions and not satisfactory electrical parameters, damping, conductivity, | ||
+ | |||
+ | |||
+ | ==== Coaxial cables ==== | ||
+ | |||
+ | Suitable to use is any high quality 50 Ohm coaxial cable with good shielding, that prevents the noise (for example from PS) to enter the receiver other than through antenna. We usually use cables of RG58 type, specifically for example [[http:// | ||
+ | |||
+ | It is recommended to use minimal necessary length of coaxial cabel, to prevent unnecessary loss of signal in the lead. | ||
+ | |||
+ | ==== SDRX01B Receiver ==== | ||
+ | |||
+ | Software-defined receiver developed primarily for radioastronomical experiments, | ||
+ | |||
+ | === Signal digitization === | ||
+ | |||
+ | |||
+ | It is possible to utilize the computer audio card with stereo imput for digitalisation of low-frequency signal from receiver. Important audio card parameter is a good s/n ratio (at least 80dB). Concerning sampling frequency, it is possible to detect meteors with 48kHz sampling, though it leads to fall in station resolution. | ||
+ | |||
+ | Due to relatively high requirements put on the quality of the sound card and its high cost, there are lately tendencies to switch to some self-made digitalization hardware. | ||
+ | |||
+ | |||
+ | ===== Software configuration ===== | ||
+ | |||
+ | The software configuration consists of two steps. The first is to tune the receiver to a frequency of GRAVES radar transmission and the second is to sett the meteor detection for receiving bandwidth. | ||
+ | |||
+ | ==== Local oscillator receiver tuning ==== | ||
+ | |||
+ | You can use [[http:// | ||
+ | with [[cs: | ||
+ | |||
+ | === LO calibration check === | ||
+ | |||
+ | When tuning the LO, it is sometimes necessary to check its correct calibration. One option is to use the VOLMET network, available in Prague at 125.525MHz (for other places see [[http:// | ||
+ | |||
+ | {{ : | ||
+ | |||
+ | The picture shows the signal tuning to 125.525MHz. LO is tuned to 125.515 and the signal is visible at approximately 10kHz in audioband. | ||
+ | |||
+ | |||
+ | ==== Meteor detection ==== | ||
+ | |||
+ | There exist only a few software tools for meteor detection in SDR receiver signal. The simplest way to begin the observation is to use SpectrumLab program and ready-made configuration file. | ||
+ | |||
+ | If you digitalize the sound card signal and use SDRX01B receiver, it is recommended to tune the local oscillator to 143, | ||
+ | |||
+ | === SpectrumLab === | ||
+ | |||
+ | SpectrumLab for on-line data processing is available at [[http:// | ||
+ | |||
+ | The path for saving the pictures, can be set in " | ||
+ | |||
+ | {{ : | ||
+ | |||
+ | |||
+ | Be careful when entering the path, as " | ||
+ | |||
+ | Moreover it is advised to fill in a suitable name of the site and coordinates of observation. | ||
+ | |||
+ | The detection script: | ||
+ | |||
+ | {{ : | ||
+ | |||
+ | The principle of its function lies in choosing an average value of noise background from frequency range 9800-10200Hz and comparing it with the expected GRAVES radar transmission intensity (10300-10900Hz). If it finds here an increase in signal intensity (by approximately 20dB), a meteor is detected. A point is marked at spectrogram, | ||
+ | |||
+ | ==== Data publication ==== | ||
+ | |||
+ | For the measured data to obtain a meaning, it is vital to share them with other observers. Several worldwide databases have been created to serve this purpose. | ||
+ | |||
+ | === IMO === | ||
+ | |||
+ | Organisation aimed primarily at visual detection of meteors. http:// | ||
+ | |||
+ | === RMOB === | ||
+ | |||
+ | You can publish the date at [[http:// | ||
+ | |||
+ | === Astrozor === | ||
+ | |||
+ | [[http:// | ||
+ | |||
+ | ====== Station parameters ====== | ||
+ | |||
+ | ===== Detection limits ===== | ||
+ | |||
+ | The sensitivity of system has not been yet experimentally tested, because of the missing data from other sources that can be used for comparison. Sensitivity is also affected by various signals - [[meteory rusenie]] | ||
+ | |||
+ | |||
+ | ===== Frequency stability ===== | ||
+ | |||
+ | The station receiver stability of frequency depends mainly on the temperature of LO. The following picture shows the temperature dependence resulting from the measured frequency deviation. The change in the frequency has been observed using the whole system with sound card SoundBlaster USB External 24bit live. | ||
+ | |||
+ | {{: | ||
+ | |||
+ | We have used Asus EEE, that is particularly suitable as portable detector. | ||
+ | |||
+ | |||
+ | ====== Other possible extensions ====== | ||
+ | |||
+ | ===== RMDS01B ===== | ||
+ | |||
+ | The equipment should be improved with better signal digitalisation method and synchronisation of LO using GPS receiver. | ||
+ | |||
+ | {{ : | ||
+ | |||
+ | ==== Specialised beacon construction ==== | ||
+ | |||
+ | The use of GRAVES radar as a transmitter for meteor detection is on one side very effective when learning how to operate the equipment, but on the other side, its parameters are not sufficient for further development and advanced signal processing (with the aim of calculating the vector trajectories of meteors). | ||
+ | |||
+ | ==== GPS time synchronisation ==== | ||
+ | |||
+ | LO of the receiver can be synchronised with GPS receiver or it is possible to mark the signal samples with [[cs: | ||
+ | |||
+ | Synchronisation and the trimming of LO can be managed using FPGA [[cs: | ||
+ | |||
+ | Trimming of the LO furthermore enables to reach a good temperature frequency stability of the system. | ||
+ | |||
+ | ==== Portable system ==== | ||
+ | |||
+ | A portable version of receiver (with accumulator power source) is suitable for field mobile meteor demonstration, | ||
+ | |||
+ | [[http:// | ||
+ | |||
+ | |||
+ | ==== Autonomous detection system ==== | ||
+ | |||
+ | Receiver and detection station, integrated together to form one whole, would lower the total power consumption of detection apparatus and would increase the reliability as well. | ||
+ | |||
+ | === Decoding computer === | ||
+ | |||
+ | The signal processing requires relatively high computational power. For this reason it is beneficial to make use of multi-core solutions. An example of such solution is following: [[http:// | ||
+ | |||
+ | === Power backup === | ||
+ | |||
+ | Another advantage of autonomous system would be the possibility to use compact power backup system, eg. with the help of [[cs: | ||
+ | |||
+ | === High time resolution === | ||
+ | |||
+ | The receiver could include high-speed circular sample buffer, that would be saved permanently in the case of event. | ||
+ | |||
+ | ==== Meteor geocaching ==== | ||
+ | |||
+ | It would be possible to handle the calculated impact ellipse as a geocache target. | ||
+ | |||
+ | ===== TODO ===== | ||
+ | |||
+ | |||
+ | * To investigate the possibility of handling the Si570 directly through SpectrumLab http:// | ||
+ | * To create .deb instalation packet for Linux station. | ||
+ | * To invent diploma theses (concerning the transmitter for meteor detection) | ||
+ | ===== Related constructions ===== | ||
+ | |||
+ | * Visual meteor detection system - [[cs: | ||
+ | |||
+ | ===== References ===== | ||
+ | * [[http:// | ||
+ | * [[http:// | ||
+ | * http:// | ||
+ | |||
+ | |||
+ | ==== Similar projects ==== | ||
+ | |||
+ | * [[http:// | ||
+ | * [[http:// | ||
+ | * [[http:// | ||
+ | |||
+ | |||
+ | |||
+ | |||
en/rmds.txt · Last modified: 2024/04/11 13:35 by kaklik