(meteorobs) Backscatter RADAR
bob alongi
bob71741 at yahoo.com
Mon Jun 2 07:19:41 EDT 2014
Another excellent source of backscatter RADAR information is D.W.R. McKinley's "Meteor Science and Engineering"
--------------------------------------------
On Sun, 6/1/14, Cliff Sojourner <cls at employees.org> wrote:
Subject: Re: (meteorobs) Backscatter RADAR
To: meteorobs at meteorobs.org
Date: Sunday, June 1, 2014, 8:25 PM
this is a
great conversation.
I am surprised no one has yet mentioned John Felding
ZS5JF's book
"Amateur Radio Astronomy" - chapter 7
details a 50MHz meteor radar
system!
he uses a 60 degree corner reflector (horn) antenna,
which is a
great choice. it takes a lot of power, 1kW or more
if you can get
it, and it takes a very good (quiet) preamp.
also check out chapter 12, "The Science of Meteor
Scatter"
Cliff K6CLS
On 2014-05-31 21:43, James Beauchamp wrote:
Hi Jay,
I've
never really liked the terms 'forward
scatter' or 'back
scatter' because both are essentially the
same thing -
reflections of RF energy. The only difference
is the angle,
and depending on the receiver/transmitter
configuration, it
will be mono-static or bi-static.
Your description is essentially a CW mono-static
radar, and
has been employed in many systems for detection
of moving
objects. If you are able to minimize the
desensitization
challenge, the product will be an audio
frequency. It also
eliminates frequency stability concerns.
Just my personal opinion, the biggest challenge
is that 100
watts, even with an optimized beam pattern
(cosecant squared
would be the best, IMHO), would not give enough
return
energy. The largest contributor to the signal
loss is the
distance, becoming 1/R^4.
Just
as a reference point,
standard terminal ATC radars push 1 MW peak pulse
into a 35 dB
gain cosecant squared antenna and still are only
good to about
70 nm range for aircraft detection. Long
Range ASR's have
to push several megawatts, longer pulse widths and
HUGE
antenna sails to extend their detection ranges to
200 nm.
The
AF Space radar at Lake
Kickapoo worked so well for us because the
estimated ERP was
about 9 GIGA watts and was CW.
A
good starting point for 6
meters would be at least 1000 watts, continuous
wave, in an
omni-directional (horizontal), cosecant-squared
(vertical)
pattern. I think that could get enough ERP for
detection by
receiving stations in a bi-static
configuration.
Waivers
COULD be considered by
the FCC if enough of a case can be made for
research.
On
that note, I noticed that
WWV is experimenting with periodic broadcasts at
25 Mhz using
kilo-watt or higher ERP. This could be another
possibility.
______________________________
Maybe I have been
thinking wrong. While it is constructive to use
Forward
Scatter RADAR for detection from many different
locations
distant from the Beacon, this technique requires
participation, there is no one participating in
Meteor
detection in my Region. My idea is to make a
Back Scatter
RADAR.
Using 2 Antennae, one
transmitting, the other receiving, it should be
possible to
mix the transmitter energy with the receiver
energy to
detect Doppler energy. Utilizing the 50 MHz
Armature Beacon
allocation at 100 Watts, I should be able to
build a test
rig for detecting Meteors. By placing two 6
Meter-band
Antennae facing upward, three meters apart,
mixing the two
antennae signals in a Double-balanced Mixer,
hopefully
Doppler Meteor activity will be
detected.
Any ideas?
On Saturday, May 31, 2014 4:16
PM, Jay Salsburg <jsalsburg at bellsouth.net>
wrote:
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Maybe I have been thinking wrong.
While it is constructive to use
Forward
Scatter RADAR for detection from
many
different locations distant from
the Beacon,
this technique requires
participation, there
is no one participating in Meteor
detection in
my Region. My idea is to make a
Back Scatter
RADAR.
Using 2 Antennae, one
transmitting,
the other receiving, it should be
possible to
mix the transmitter energy with
the receiver
energy to detect Doppler energy.
Utilizing the
50 MHz Armature Beacon allocation
at 100
Watts, I should be able to build a
test rig
for detecting Meteors. By placing
two 6
Meter-band Antennae facing upward,
three
meters apart, mixing the two
antennae signals
in a Double-balanced Mixer,
hopefully Doppler
Meteor activity will be detected.
Any ideas?
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