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Re: (meteorobs) Radio Meteors
In typical Lewis fashion <grin>, the questions continued with:
>Jim, to what extent is the equipment for this type of monitoring accessible
>to the amateur who is just starting out or unsure of their commitment to
>radio meteor monitoring? Translated: how much of the required equipment for
>carrier wave scatter monitoring is available at Radio Shack for under
$100? :)
>
Not much. The FM station route is generally the cheapest way to go, and
usually yields the most easily attainable results.
An alternative low-price method which would allow some casual listening to
the carrier wave form of meteor echoes would be to find a used or
inexpensive Shortwave receiver -- making sure that the receiver can
function in the CW (continuous wave) or SSB (single sideband) modes. You
must also be able to hook up the receiver to a long-wire antenna,
preferably outdoors. Using this simple setup meteor echoes can be
detected, provided that a suitable frequency and distant transmitter is found.
The problem with this band is that it is extremely "flaky;" in that it
changes its propagation characteristics day by day, and sometimes hour by
hour. A frequency which work for meteor echoes in the morning may be
swamped in the afternoon. Meteor Group Hawaii (MGH) had better luck in
their relatively isolated Pacific location during a sunspot minimum, but
this is a rather atypical situation. They used distant time broadcast
(WWV) stations as their signal source.
For further reading see:
Lynch, J.L., (1992, August). A Different Way to Observe the
Perseids, Sky and Telescope, pp. 222-225.
Mason, J., (1994, February). Tuning in to meteor showers,
Astronomy Now.
Now for the second question:
>Jim's answers regarding signal strength make it clear that this would not
>be feasible with most amateur equipment. But I wonder if the pulsar (or
>perhaps some of the other strong sources, such as Sag A) would be
>detectable at appropriate frequencies to make meteor scatter possible with
>professional equipment? Pretty obscure question, but cloudy days always
>make me curious. :)
I don't think that this would work, even with professional equipment, for a
couple of reasons.
1. Successfully detecting a meteor echo generally requires a rather
coherent, uniformly polarized signal source. Distinguishing the meteor
echo from the radio background would not be easy for most celestial
sources. A strong pulsar might do it, but the resulting echo would be
pretty brief and faint. Not to mention that your "transmitters" are now
roaming across the sky, with a constantly changing geometry.
2. The meteor trail typically adds another 30 to 80 dBm of signal loss to
the reflected signal, burying these alread faint signals that much deeper
in the noise. Even with the extra-ordinary sensitivity of professional
equipment (Arecibo can reach -180 dBm!) this would not be a very practical
experiment.
Sort of along these same lines, however, I have heard of professionals
successfully utilizing radio transmitting satellites as the signal source
for meteor forward scatter (stationary?), although I can't point you to any
papers. I don't know of any amateurs who have been able to do this also,
although Dr. Meisel mentioned it as a possibility in the original 1977
version of AMS Bulletin 203. Most of these satellites today are designed
for line-of-sight, high-frequency communication and do not give themselves
over to meteor scatter very easily. It is interesting, but transmitters
here on the ground are usually more practical.
Here's hoping for clear skies in New England...
Jim
James Richardson
Graceville, Florida
richardson@digitalexp.com
Operations Manager / Radiometeor Project Coordinator
American Meteor Society (AMS)
http://www.serve.com/meteors/
References: