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Re: (meteorobs) Radio Observation of Meteors

At 10:08 AM 8/22/99 , you wrote:

>> I'm not certain of what you're getting at here. Would the beacon send a
>> time code (one of the IRIG codes, say, the one that uses a 10 kHz carrier).
>> The receiving station could then calculate the dealy of the time code and
>> determine the total path length.
>
>Yes, some form of timing mark, or both transmitters and receivers
>synchronized to a LORAN master station for example.

Sync with LORAN or GPS--I think TAPR has a kit that will allow you to build
a 10 MHz dsciplined oscillator that is synchronized to GPS/atomic time. The
advantage of an AM code such as IRIG is that you can raise your timing
precision by examining phase. Since the entire received burst contains
phase information, you increase the number of points used to calculate time
delay and improve your statistics considerably. If you used a binary phase
code or a timing mark, you may have difficulty determining exactly when the
transition occurred.

>> I think you'd lose a lot of data if you only ran 100 W, though. At 25 kW at
>> 50 MHz we had plenty of signal to work with for most meteors, but about
>> 10-20% were too far down in the noise to be useful for analysis (we were
>> looking for atmospheric density and wind data, not doing meteor astronomy
>> at the time).
>
>	I was thinking of restraints of doing something like this within the
>amateur radio bands, and within the budget of amateurs.  In my case I
>couldn't afford the power bill for a 25 kW transmitter :-)

Sure you could! The one we used was a ham design--it was a 2.5 kW PEP amp
run at a low duty cycle, yielding a PEAK power of 25 kW . . .

>I'd like to
>hear more about how you did the atmospheric density and wind data. 

We used a 5 channel interferometry receiver to get angle of arrival. We
knew the range because it was a backscatter radar system. Dopplers yielded
radial wind velocity and exponential decay rate of the echo was
proportional to atmospheric density.

>Regrettably the information that I have on hand is limited to McKinley's
>book, Meteor Science and Engineering.  Peak transmitter powers at that
>time ranged from 1 kW to 100 kW, with the (I guess state of the art in
>the late 1950's) Springhill site using 20 kW pulses (30 W average) on
>32.7 MHz.

>	Myself, to set up an experimental system I'd have to do it as a 
>licenced beacon within the amateur bands. Therefore it would likely have
>to operate on 430 MHz or above - to be able to pulse modulate or wide
>band FM modulate the beacon for timing.

Or, you could run several beacons in lower frequency band (28, 50, or 144
MHz), each one at a a slightly different frequency and each of them runing
a different time coding scheme. Colocate all beacons (5 beacons = 500 W!)
and give each beacon its own antenna (duh). 

For time coding you could almost do something as simple as an AM modulated
tone. Each beacon would have its own modulating sequence and each beacon
would have its own tone. If the tones were prime to each other, you could
get high time resolution with a system that had a low enough bandwidth to
use at lower frequencies. 

>	Operating on UHF of course is a compromise too, weaker reflections, but
>higher gain antennae and fewer problems from ionispheric refraction
>(which probably wouldn't be much of a problem with such a high angle of
>radiation).

I have seen 1000s of meteors at 430 MHz and no meteor trails (using the
Arecibo radar). Granted, it has an extremely narrow beam, but it does see
the meteor head echos. Unfortunately, none of us has the resources to build
a 1000 foot dish and feed it with a 400 kW klystron!

>	As I'm out of the information loop I'm not current on what has been
>done since McKinley's book (1961) was written.  I would appreciate more
>current information or to be directed to where I could find out more on
>either government funded projects or amateur work on direct detection
>techniques.

If you're interested in references on meteor radars, drop some email to my
boss, Frank Djuth djuth@ixdot netcom.com He'll have the latest references,
both in meteor radars for atmospheric study and for meteor astronomy.

73,

John
KO6X

PS We're working on a proposal to use HAARP as a meteor orbit radar. There
are technical problems as HAARP cannot pulse as per their spec yet. In
theory we'll be able to get 10 us pulses near 10 MHz running ?? MW of power
and receive with a 16 receiver digital sysem . . . I'll keep you posted--we
just started the software for the prototype (2 channel) receiver. The
entire system will take a few years to get funded and running.
====================
Visit: http://www.jelder.com
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One does not become enlightened by imagining figures of light,
but by making the darkness conscious.

	-- C. G. Jung

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