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Re: (meteorobs) meteor detection in AM SW band
Marcelo,
I use a 6 meter amateur transceiver (capable of tuning to approximately 60
Mhz). The receiver must be capable of receiving CW (continuous wave--or
morse code) or SSB (single sideband) mode.
I tune to the video carrier frequency of television stations in the region.
Ideally, the station should be located more than 150 miles (220 km) from my
location. The video carrier signal is AM, amplitude modulated.
Monitoring for forward meteor burst must be done on frequencies above 30
Mhz, ideally above 50 Mhz because these frequencies are "line of sight" in
other words they don't normally travel much beyond the local horizon. Below
50 Mhz signals will refract, or bend over the horizon or "skip", bouncing
off the ionosphere. You do not want to hear such a "sky wave" signal, you
only want to hear signals which have reflected off the ionized meteor trail.
For this reason "shortwave" signals (2-30 Mhz) are not useable for meteor
burst work.
The television video carriers are very good "signal beacons" for meteor
burst work. They are high power (normally on the order of 50kw to 100kw
power), stable, amplitude modulated and on most of the time and there are
multiple signals on so meteor "pings" will bounce off different carrier
signals coming from different directions. They are also on the "right"
frequency (see above). Because I have a local "Channel 3" (60-66 Mhz) I use
TV Channel 2 for my meteor burst monitoring. The nearest station is about
150 miles away.
Because the video carrier is AM (amplitude modulated) there is a constant
carrier wave. With my receiver in CW mode a meteor burst will be heard as a
tone. I hear the burst as a "beep" that doppler shifts up or down depending
on the direction of the meteor.
This is my preferred mode for monitoring meteor burst. It can be done
another way. You can also listen on the FM broadcast band. I don't know
where you live. Here in the States that is 88-108 Mhz. In other countries it
is 76-108 Mhz. Monitoring FM broadcast is similar except you tune to a frequ
ency that is not occupied by a local station. You will hear brief "bursts"
of the signals from distant stations, usually lasting less than 1 second.
This method works, but the TV method using 54 Mhz signals is preferred
because you normally get longer bursts at the lower frequencies and
reflections from smaller "pebbles" (meteoroids) can still be heard clearly.
The FM broadcast band method does work, however.
Hope this helps. If you have any other questions please feel free to write
again.
Regards,
Mark S. Williams
Amateur Radio K9GX
k9gx@n4gn.com
Harrison YMCA Astronomy Group
astronomy@n4gn.com
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