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Author Topic: Boltek Lightning Detectors - technical query.. how do they work?  (Read 5430 times)

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Offline EI4HQ

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Hi,

I've a background in radio comms and am intrigued about how Boltek are (claiming) to be able to detect both bearing AND range to a lightning strike - does anyone know what the assumptions they use when determining these two pieces of data?

I'm absolutely fascinated how a single 'tiny' antenna can provide the basis for the directional accuracy they claim - I'd be delighted to be proved wrong, but it seems a big claim to defend.
Cormac (EI4HQ)
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Offline TNETWeather

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Re: Boltek Lightning Detectors - technical query.. how do they work?
« Reply #1 on: August 11, 2005, 07:16:32 PM »
Its most likely best to check their website for technical info on their product.

I have one and it works pretty good.  There are some limitations which are expected, but it works very well.

http://www.tnetweather.com/weather-lightning.php


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Offline niko

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Re: Boltek Lightning Detectors - technical query.. how do they work?
« Reply #2 on: August 11, 2005, 07:20:39 PM »
I've always wondered about that antenna too, even been tempted to buy one and open it up. My best guess is that it contains two ferrite antennas at right angles. I have seen information that the Boltek ranging is based on the amplitude of the signal, some other detectors measure the time difference between the signal at different frequencies.

Offline TNETWeather

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Re: Boltek Lightning Detectors - technical query.. how do they work?
« Reply #3 on: August 11, 2005, 07:42:13 PM »
How does StormTracker detect lightning?
StormTracker detects the low frequency radio signals produced by lightning's electrical discharge. This signal is the crackling you hear on an AM radio when thunderstorms are nearby. These signals travel for hundreds of miles and are detected by StormTracker's antenna.


How does StormTracker know where the lightning is?
StormTracker uses a direction-finding antenna to determine the direction the lightning signal came from. StormTracker's receiver looks at the signal strength to calculate an approximate distance for the lightning strike. There is additional processing done in software to reduce the effect of strike to strike magnitude variations. Once StormTracker knows the direction and distance of the strike it plots it on the map.

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Offline administrator

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Re: Boltek Lightning Detectors - technical query.. how do they work?
« Reply #4 on: August 11, 2005, 08:00:15 PM »
How does StormTracker detect lightning?
How does StormTracker know where the lightning is?

I think Cormac was interested in the technology behind the blurb. At the kind of frequencies that the unit is monitoring antennas are usually huge (wavelengths in hundreds or thousands of metres) and small antennas (in wavelength terms) often have unusual radiation/reception patterns which would make it difficult to work out where the signal came from.

Like nikoshepherd, I wonder if ferrite antennas are used, but if there are only two then directivity would be tricky. Ferrites tend to have two strong nulls and two strong peaks in opposite directions. So if you had two ferrites at right angles you might get a good signal off one and almost none off the other. This would only give you (for example) a North or South direction with no way of knowing which it was.

I suspect that there's something more than just ferrite antennas in the 'block'. Mine gets warm to the touch which suggests there's something significant going on inside it (active antennas of some sort?) A couple of ferrite antennas with attached receivers wouldn't generate that much heat.
Chris
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Offline niko

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Re: Boltek Lightning Detectors - technical query.. how do they work?
« Reply #5 on: August 11, 2005, 08:14:34 PM »
Agreed. Normally there would be a vertical antenna to handle the directional ambiguity of crossed loops like this one http://www.tcibr.com/PDFs/7235webs.pdf but I have seen some papers which did some very fancy signal processing to get the same result. I have also seen a paper about a df antenna using a square ferrite loop, mounted horizontally, with 2 or 4 windings and some electronics. All the signal processing has to happen in the box since it's just a plain old cat 5 type cable output - right?

Does the cover come off?  :lol: Probably find it's epoxy encapsulated.

Updated: Seems to be a flat plate rather than a vertical antenna in the Vaisala professional detectors, but it would be a very small plate in that boltek box...

Quote
The magnetic direction finder (MDF) senses the electromagnetic field radiated by a lightning flash using two erect, orthogonal wire loop antennas and a horizontal flat plate antenna. The radiated field of a lightning flash induces a current in the loops. The voltage signal measured in the loops is related to the flash's generated magnetic field strength by the cosine of the angle between the loop antenna and the direction to the flash. By comparing the voltage signals from the two loops, a direction to the flash can be determined. The flat plate antenna is used to resolve the 180 degree ambiguity associated with the calculations.


from http://nofc.cfs.nrcan.gc.ca/science/research/lightning_e.html
« Last Edit: August 11, 2005, 08:32:43 PM by nikoshepherd »

Offline Weather Display

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Re: Boltek Lightning Detectors - technical query.. how do they work?
« Reply #6 on: August 11, 2005, 08:38:03 PM »
so i can see a lbajack version coming out soon then?
(as the labjack can do some very fast processing and can handle very small voltages too)

Offline administrator

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Re: Boltek Lightning Detectors - technical query.. how do they work?
« Reply #7 on: August 11, 2005, 08:48:20 PM »
Probably not...the processing is likely to be mathematical signal processing which I don't think the LabJack can do on it's own.
Chris
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Offline Weather Display

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Re: Boltek Lightning Detectors - technical query.. how do they work?
« Reply #8 on: August 11, 2005, 08:56:45 PM »
dang!
what about of you hook up virgils burnt out cpu to the labjack, and use whats left of that?  8O

Offline niko

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Re: Boltek Lightning Detectors - technical query.. how do they work?
« Reply #9 on: August 11, 2005, 09:02:31 PM »
dang!
what about of you hook up virgils burnt out cpu to the labjack, and use whats left of that?  8O

Looks like that was a one time use lightning detector  :lol:

Offline ricky

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Re: Boltek Lightning Detectors - technical query.. how do they work?
« Reply #10 on: August 12, 2005, 09:28:19 AM »
The E field antenna could be very small, just need a higher gain amp on it... 
I too have often wondered what exactly is in that antenna, out of interest I looked at the signals on the connecting cable.. at that stage they are still reasonably wideband analog, ie there was a fair bit of am radio along with the noise.. certainly a lot of gain up top, I would guess maybe some sort of log amp to deal with the huge dynamic range of signals.. as well as some pre-filtering..

Offline Weather Display

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Re: Boltek Lightning Detectors - technical query.. how do they work?
« Reply #11 on: August 12, 2005, 10:50:31 AM »
wouldnt be great if you some of your electrical whiz kids could all meet up one day :)
and swap stories  :wink:

Offline administrator

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Re: Boltek Lightning Detectors - technical query.. how do they work?
« Reply #12 on: August 12, 2005, 12:05:39 PM »
We meet up here and exchange stories!
Chris
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Offline EI4HQ

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Re: Boltek Lightning Detectors - technical query.. how do they work?
« Reply #13 on: August 13, 2005, 07:26:08 AM »
Thanks for all the responses - yes its the tech-behind-the-blurb that I'm interested in.

I thought perhaps a couple of crossed ferrites might be the answer but couldn't see how the kind of directional accuracy being implied was possible with a setup of that sort - any of you familiar with older ship's navigation equipment might remember MF RDF - not exactly an accurate position fixing technology! Hence I suspected there might be something else going on.

From the blurb the following facts are clear
(i) the antenna is active (hence the heat methinks)
(ii) distance is derived from signal strength

Whatever about directional accuracy (which I have suspicions about) the distance can't be terribly accurate - propagation, local interference, etc. will see to that.

I note with interest that the professionals use multiple direction finding stations and triangulate to achieve an approximate position for a strike, thereby eliminating the need to determine distance using other means. I wonder if Boltek could do this by linking customers via their software & the web...
Cormac (EI4HQ)
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Twitter: @CorkHarbourWX
[Cobh / UTC+1] NNNN++++

Offline Weather Display

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Re: Boltek Lightning Detectors - technical query.. how do they work?
« Reply #14 on: August 13, 2005, 07:38:35 AM »
Quote
I wonder if Boltek could do this by linking customers via their software & the web...
they are doing that now, its called strikestar  :wink:

 

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