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[wxsig] Array of X1W-4 sensors to detrime direction and distance ?

William Beals will at beals5.com
Wed Feb 13 05:21:25 UTC 2008


Anything based on EMF is going to be pretty tough to measure accurately with
consumer grade stuff.  Back when I did high speed stuff a good rule of thumb
was the speed of light is around 1ns per foot, so assuming you want to
measure something accurately to a quarter mile, all your measurements are
going to need to be accurate to better than 1300ns or 1.3us.  And--that
doesn't include the time to get all the signals from the 3+ sensors back to
a central place to get timed relative to each-other!  

If (while dreaming) I had been asked to dream up such a system, I'd also
question if you could accurately relay a detection signal as at the instant
you detect a bolt and want to send a signal saying you heard it, that
instant would be a really tough time to send a signal over any band as the
lightning itself would be trashing most of the spectrum.  I think a better
bet would be to have really accurate clocks at all 3+ locations, measure a
time stamp and then send that timestamp non-real-time after the lightning
hit.  A quick look at Garmin's website shows their OEM receivers give a one
pulse per second output accurate to 1us, so at least you are getting close.

I also worry about measurements in terms of 2D vs. 3D space.  If you can
somehow rationalize lightning as occurring at a point on a 2D plane, 3
antennas would be fine, but lightning is very much 3D, not a point source of
noise, nor a simple pulse, so interpreting the data from the sensors may
involve more than measuring a simple edge time.

Fun thing to think about...  Especially doped up on antihistamines!


-----Original Message-----
From: wxsig-bounces at lists.tapr.org [mailto:wxsig-bounces at lists.tapr.org] On
Behalf Of Stanley Reynolds
Sent: Tuesday, February 12, 2008 6:03 PM
To: TAPR Weather Station SIG Mailing List
Subject: Re: [wxsig] Array of X1W-4 sensors to detrime direction and
distance ?

Some searching turned up this site : www toasystems com
Some answers but still not sure how practical a simpler solution is, looks
like they are using at least 3 sensors separated by several KM. 

I know the US military is using passive sound to locate small arms fire,
wonder if sound with it's slower speed would make a range and direction
measurement more practical for a local < 50 feet separation array ? Would
obviously reduce the detection range vs RF.

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