[Prev][Next][Index][Thread]
Re: (meteorobs) radio detection
At 09:01 AM 08/13/98 -0700, Dale Ireland wrote:
>Yes they produce radio waves. They produce electromagnetic waves in the
>VLF and ELF (very and extremely low frequency) range around 10 to 60 Hz
>(that's Hz not KHz). This low frequency radio energy has been know to
>induce vibrations in metal objects (like your glasses frames) producing
>sound waves (very rare).
Radio amateurs have also noticed increased noise on some frequency bands
such as the 21, 28 and 50 MHz ham bands as some meteors have generated
ionized trails. This will not be noticed with an ordinary FM broadcast
receiver which is not sensitive to amplitude modulation (AM), but can with
an ordinary shortwave receiver using AM or SSB/CW modes. The noise might be
due to the many transmitted signals being reflected causing intermodulation
distortion within the receiver itself; but this effect has also been
noticed on the 144 MHz band from time to time where the number of such
strong signals is much less.
Because this HF/VHF noise is uncommon, it is not usually a good indicator
of a burning meteor.
BTW, there were several hundred radio hams in North America very active for
the Perseids this year. The consensus seems to be that the radio peak
occurred between about 1430Z and 1500Z 12 Aug, providing exceptional
although short-lived reflections over mainly 1500 kM paths. Long-haul paths
to 2000 kM were also somewhat enhanced for those with larger antennas but
to a much lesser extent. Throughout the shower, long-haul contacts have
occurred with very many strong and long reflections nor normally encountered.
But there is also the perception that the 1998 Perseids has been somewhat
below the already-dismal performance of the 1997 Perseids. More information
later as it comes in.
Clear skies,
SteveH
Shrewsbury MA
References: