How to tune in to the shooting stars? The Doppler method can be tried by anyone with only:
ESA/RSSD/MRG Radio Observations
a shortwave receiver with SSB capability
a PC with sound card
audio software for accessing the sound card, recording the wave file and displaying dynamic spectrogram (standard Windows software for recording, or free software on the web for recording and processing)
The radio receiver is tuned to a station around 500 km or so away. It is set to USB mode, 1 kHz below the frequency of the transmission (e.g. at 17639 kHz for the BBC transmission at 17640 kHz). If you prefer to work in LSB mode, you should tune in at 17641 kHz. Switch to SSB mode, and start the software. The audio output of the receiver contains a line at 1 kHz and the voice modulation appears above and below the 1kHz line. Amateur radiometeor observers can use a simple PC controlled communications receiver like the one shown in next figure.
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|Radio receiver: ICOM ||PC interface |
Standard PCs with sound card are suitable for the experiment.
The software uses the sound card of the PC to record and analyse the signal. All that is needed is a connection from the headphone output of the radio receiver to the PC's sound card input.
Some SW applications are available on the web for this purpose:
GRAM (http://www.visualizationsoftware.com/gram.html): full audio spectrum. Allows:
- detection of meteors during entry phase, most spectacular during night
- count meteors
- calculate the deceleration profile of the meteor along the line of sight based on the slope.
Gram50 spectrogram example (recorded in Noordwijk at about 22:20 Local Time).
R_METEOR (http://www.coaa.co.uk/r_meteor.htm): 1 sec resolution high resolution Dopplergramme in a narrow bandwidth around 1 kHz carrier.
- Doppler echo due to the deposited plasma cloud moving in winds.
R_meteor dopplergram example (bandwith 30 Hz around carrier)
Depending on what you want to be visualised, you should select between two different frequency ranges.
- For the Entry Phase, display the dynamic spectrogram of the audio signal in a band of few kHz around 1 kHz. Typically the frequency band displayed is 0 to 3 kHz.
- For the plasma cloud drift, it is sufficient to display the spectrogram of the audio signal in a narrow band around 1 kHz. Typically the frequency band displayed is a few 10’s Hz wide.
All you need now are the Meteors!
Udo, PA3EZI, using the club station PI9ESA to listen to the Leonids 1999.
Photograph: J-P. Lebreton.
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