[Prev][Next][Index][Thread]

Re: (meteorobs) Radio Observation of Meteors



Hello Ron, et al,

As far as I know, no amateur radiometeor enthusiast has yet established a
true pulse-type meteor radar.  The closest thing to this was the 75 MHz
system pioneered by Bill Black (1983) for the AMS, which utilized
vertically directed airport ILS beacons, with transmitter and receiver
separated only by a few miles. These beacons were used for the old "outer,"
"middle," and "inner" instrument panel lights for an aircraft on final
approach, and were physically located at 10 miles from the runway, 5 miles
from the runway, and just short of the runway, respectively.  The
transmitted power was only 20 watts, in a repeated CW Morse code format.
For example, if I recall correctly, the middle marker sent out a continuous
string of the letter "A."  I got to work with this type of setup as a
member of Meteor Group Hawaii in the late 1980's, in which the mobile
receiving system was set up on the opposite side of Oahu from the airports,
with a 2000-3500 foot high volcanic ridge in between to separate the
receiver from the transmitter ground wave (although diffraction could still
be a problem).  At the time, the only information which was being recorded
was meteor rate data, and that either manually or via strip chart recorder.
 However, this type of system can no longer be used, because the FAA
required all airports to modernize these beacons in the early 1990's,
reducing their power output to only about 3-5 watts -- rendering them
useless for meteor work.

There are some short range CW forward-scatter systems, using the 6-meter
amateur band, established in Japan that I know of, but the majority of
amateur operated systems are long range forward-scatter systems which
utilize existing commercial transmitters as a continuous CW or FM signal
source.  Many have automated systems for meteor echo detection, and record
such information as occurrence times (or rate per time bin), peak echo
power, and echo durations.  There is a system in Belgium (University of
Ghent) which also does full digital echo signature recording.  Last year,
Werfried Kuneth and I became the first amateurs to attempt meteor range and
speed determinations from a forward-scatter link, described in:

Richardson, J.E., and Kuneth, W., (1998, June).  "Revisiting the Radio
Doppler Effect from Forward-scatter meteor head Echoes," WGN, Journal of
the International Meteor Organization, (No. 26:3, pp. 117-130).

The drawback in this method is that it requires rather special conditions
(a Doppler shifted meteor head echo), a rather simple model with
assumptions, and cannot be done automatically.  In this same vein,
underdense echo signatures might also be used to obtain rough speed/range
information from the post t0 diffraction pattern, provided that the
receiver power level detector used (such as an AGC circuit) and digital
recording system have millisecond type resolution.  Using standard,
commercial CW receivers, there is not enough gleanable  information per
echo to obtain more detailed parameters from a single one antenna receiving
station.  

More advanced systems, such as true pulse-type radars, interferometry
setups for determining echo directionality, or single transmitter /
multiple receiver systems have not yet been established by amateurs (again,
that I know of).  You would be pioneering in this area if you attempted it.
 i do think, however, that if you check your equations in McKinley and
elsewhere, that a low-powered 430 MHz system will not give back detectable
meteor echoes.  There are two UHF professional systems in operation,
Arecibo (Puerto Rico) and EISCAT (Sweden), but these use a LOT of power to
do so  (Arecibo is at 2 Megawatts) -- far beyond realistic amateur
capability.  Most professional meteor radars today still stay in the HF /
VHF bands, transmitting in the low kilowatt power output range.  Your best
chances for success are probably to stay within either the 10-meter or
6-meter amateur bands.  Best of luck!

Regards,

     Jim



James Richardson
Tallahassee, Florida
richardson@digitalexp.com

Operations Manager / Radiometeor Project Coordinator
American Meteor Society (AMS)
http://www.amsmeteors.org

To UNSUBSCRIBE from the 'meteorobs' email list, use the Web form at:
http://www.tiac.net/users/lewkaren/meteorobs/subscribe.html

Follow-Ups: References: