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

Wed Feb 13 06:23:08 UTC 2008

----- Original Message ----
From: William Beals <will at beals5.com>
To: TAPR Weather Station SIG Mailing List <wxsig at lists.tapr.org>
Sent: Tuesday, February 12, 2008 11:21:25 PM
Subject: RE: [wxsig] Array of X1W-4 sensors to detrime direction and distance ?

Stanley:

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!

will

Yes I was thinking processing the data sometime after the event several min would be OK. I have some GPS units like you describe, Garmin GPS 25-LVC. Also have 3 sites about 50 miles apart. The X1W-4 sensor should supply pulse length which could be used to id the strike from other noise sources. Guess a redesign  of the sensor that supplied area under the curve or the derivative/slope of the wave form would help too. Or in simpler terms magnitude of the signal over it's duration vs a simple off/on. 

Getting back to simple maybe a computer version of counting the time between the EMP and the sound arriving at a microphone. Backed up with a photo cell array for nite time use in determining general direction.

I remember a 2 meter DF antenna that used two antennas less than 3 feet apart and switched between them at a fixed rate using pin didoes to produce a tone that was like the Doppler shift ( maybe phase difference ) to determine direction. It would be much simpler to keep the project at one location as to leave out time measurement and transfer of data.

It is late for me so I will sleep on it, thanks for the reply hope your head clears soon.

stanley

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