Radio Meteor System Description

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 First a bit of information about how radio waves propagate.   When they leave a transmitting antenna, radio waves propagate in a straight line and unless they are reflected or bent, they pass out of the atmosphere and into space and are therefore not detectable over the horizon.  However, at low frequencies such as AM and short wave broadcast frequencies, radio waves can  be refracted by the ionosphere and reflected back down to the earth past the local horizon.  This effect varies with frequency and time of day.  For our purposes, we want to tune to the frequency of a transmitter that is sufficiently distant and high in frequency that it is not normally detectable at the receiving locaiton.  It also needs to be close enough that a meteor trail in the upper atmosphere is visible to both the receiving and transmitting site.  Under those conditions, the receiver will be able to detect the transmitter when a meteor produces an ionized trail in the upper atmosphere. 

Television transmitters on analog TV channel 2 make ideal transmitters for the study of meteor echos.  The video carrier at 55.250MHz is fairly strong and the frequency is sufficiently high to make them weak to undetectable at distances that are still close enough to be able to detect the ionized trail of a meteor passing between the transmitter and the receiver. 

Fortunately, at my location in the northern suburbs of Detroit, there are still several Canadian stations on analog channel 2.  This may change soon, but for now it is easy to detect radio meteors.  I have not tried using the signal from a digital television transmitter. 

My system is fairly simple.  I use a Kenwood TS-480 amateur radio transciever as the receiver.  It is an amateur radio transciever with an excellent receiver but any receiver that can tune to 55.249MHz (USB) will do.  The antenna is a non-directional halo on the roof.  That setup alone is sufficient to detect and analyze meteor echos by ear.  To produce a spectrogram and analyze the echos visually, I use a free program called Spectrum Lab.  The audio output from the receiver is connected to the sound card on my PC and Spectrum Lab does the rest. 

In operation, I tune to 55.249MHz USB, which produces a 1KHz tone from the 55.250MHz channel 2 video carrier if the transmitter is not completely inaudible at my location.  Meteor echos are generally Doppler shifted upwards.  Audibly they sound like pings, or if the trail is sufficiently intense, they sound like a quick chirp as the meteor decelerates, followed by a steady tone as the traail dissipates.  Visually, they show as vertical lines (the chirp) followed by a horizontal line (the echo as the trail dissipates).  



Paul Goelz
2010

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