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RE: (meteorobs) Radar equipment to monitor meteors

If you are using forward scatter, you use the full
power of the broadcast station which can be very
large and free.

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From: 	Steve Harrison[SMTP:ko0u@os.com]
Sent: 	Saturday, December 13, 1997 6:15 PM
To: 	meteorobs@latrade.com
Subject: 	Re: (meteorobs) Radar equipment to monitor meteors

At 04:54 PM 12/13/97 EST, you wrote:
>Second reply:
>I think that a meteor would be to small in order
>to track by radar,

Radio waves are not reflected from the very small meteor body itself; but
rather, from the much larger plasma trail that the meteor generates as it
burns up in the atmosphere. I don't know how large that trail is in physical
size (Jim Richardson, help!!); but almost any visible meteors leave trails
that reflect low-power 28 MHz signals, while a very few extremely-high
velocity meteors can leave trails which will reflect as high as 432 MHz.

>... but again if you had enough
>power to send out to it so that it would bounc
>back

At 28 MHz, many CBers with 3 or 4 element yagi antennas make contact every
morning via meteor scatter (forward-scatter) with power levels of only a few
watts to several hundred watts (or more). At 144 MHz, I've completed a few
meteor scatter contacts with stations over 1200 kM away with just 25 watts
and a 13 element yagi antenna on my end. At 432 MHz, it took every one of my
450 watts and a 22 element yagi antenna to complete a contact between
northern Virginia and a station in southern Mississippi several years ago.

Forward scatter over the horizon incurs considerable path loss; the loss
increases over a one-way path by the square of the distance. If you were
operating a meteor radar, you would probably be pointing nearly overhead and
the path loss would be considerably less due to the much shorter distance
(about 500 to 1000 kM to a meteor on the horizon for a two-way,
forward-scatter contact versus less than 220 kM when pointed directly
overhead for backscatter with a meteor radar). So, it is apparent that the
required power for a meteor radar can be even less that that required for
two-way communications. I would think you would do quite well with only 100
watts in the 144 MHz band, and 400 watts in the 432 MHz band.

>... then it might work. It will cost many$$$$$.
>to set something up like that.

As I mentioned earlier, such a system is technically easy to design and
build and parts are readily available; the cost need not be any more than
what a typical amateur radio station costs. The only real catch is
processing and displaying the data, particularly in a scientific manner.

SteveH
Shrewsbury MA
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