Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

inquiry about lightning

Status
Not open for further replies.

ojahkatak

Newbie level 5
Joined
Aug 1, 2005
Messages
8
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,352
hai.. i'm Fauziah from malaysia.. do any of you have information/ proof that lightning radiation emit frequency as AM wave..thank you..
 

hi,
scientist worldwide had been trying all ways to grasp the wonders of nature, and trying to predict the wrath of mother nature before it strikes.

I don't think one could narrow it down to the exact modulation method ( AM, FM etc..) or any frequency etc.. but many would universally agree that there are some obvious ions activities before lightening strikes.

Try to search googles for "lightning" etc.. you can find many resources/links related to your topics.

Hope it helps!
 

Hi,

As far as I know, all lightening does is emit a massive pulse of wide-band EM. To talk about 'modulation' methods implies that it has a constant frequency and 'shifts' it in some way (either amplitude or frequency). But it doesn't. The frequencies, (and thier amplitudes) that lightening causes are virtually random. Much in the same way that car ignition systems, and lighting switches emit RF (which interferes with AM radio, but generally not FM). But of course, the EM radiation from lightening is far more powerufl than those examples. After all, its just a massive spark, so search google fro 'spark gap' and 'EM radiation'.

Now, when you say 'emit as an AM wave' is weird. What does an AM wave look like? Its a constant frequency that varies in amplitude. Whereas FM varies in frequency around a centre frequency. As I said, lightening emits neither. But.... it does interfere with AM radio, because of the wideband emission, its probable that the frequencies for many AM radio stations are also produced, and AM receivers will pick this up, because they are designed to detect changes in amplitude. FM receiver may be interfered as well, but to a lesser extent, since they are not designed to look at changes in amplitude, only frequency, this is why FM radio is considered much more reliable and less noisy compared to AM. Since nearly all 'natural' RF noise affects amplitude, but rarely frequency.

Hope this helps.


BuriedCode.
 

About 30 years ago there was some research effort on triangulating lightning at sea from shore stations. The baseline was several countries apart. They used wide band receivers and cross correlation in the time domain.

The motivation was to identify storms at sea and tell ships what areas to avoid.
 

Recent research suggests that lightning is not just a huge spark, but is a more complex runaway breakdown phenomenon. Ordinary sparks require about 3 megavolts/meter, but lightning occurs at only 200 kilovolts/meter. Ordinary sparks don't generate X-rays and gamma rays, but lightning does.

Fun reading in May 2005 Scientific American magazine.
 

I recall a documentary a few years ago. Using very high speed cinematography they showed that bolts of lightening start at the ground and grow up to the clouds.

Electricity companys have had system to detect the location of lightning for years.
There are some online lightning radar's such as this uk one
 

hi again,


echo47, I believe that the v/m for sparks isn't linear. There are more factors than voltage (humidty, air pressure, pollutants) that can change the require potential for a 'cascade'. And of course, due to the vast difference in scale, you can't expect to simulate lightening with sparks under 10 feet.

I'm no expert, but as far as I know, the potential in a storm cloud reaches a massive figure. And, 'sparks' are not just air carrying electricity, first the air must be ionized, and its the potential that does this. Ionzing a lot of air around the cloud, and 'repeling' electrons on ground objects. A ground object (usually many) fire up 'streamers' which are long (6 feet?) channels of positively ionized air, caused by the massive potential above, but they have hardly any current. Like the sparks you get from a CRT screen (old TV) just bigger. The cloud also emits a streamer, but of course, because neither streamer in actually in contact with anything of different potential, little current flows...until.......a streamer from the ground (or ground object) makes contact with the cloud streamer.

This completes the circuit, and current flows (from ground to cloud), draining the cloud of its static electricity, a massive current surge super heats the air in the ionized channel, making it expand violently.

I'm sorry for calling lightening a 'big spark', but for the purposes of this topic (RF interference, wideband EM) its convenient to think of it as such.

anywya, regardless of why people are interested in lightening, theres been great advances in research in the past 10 years. And its all on google.

BruiedCode.
 

I haven't found much recent (since 2003) information from Google searches, except for news reports of recent observations. An ordinary ionized air discharge model doesn't properly explain the observations. There are various theories about relativistic electons, cosmic ray triggers, and other exotic stuff. Something weird is going on in there. Scientists are having fun trying to sort it out. ;)
 

echo47,

I know I'm probably moving far away from the original post, but I like discussing lightening :)

I forgot to mention something else....the Jacobs Ladder.

I agree that conventional model's cannot explain the lightening process accurately. But the Jacobs ladder can achieve a spark length 4 times greater than a simple spark gap with the same voltage. The spark moves up because it heats the air (hot air rises) creating a lower pressure, but ALSO...a spark generates lots of UV, which ionizes the air around the spark, lowering resistance, and lowering the required voltage for a spark to occur at that distance.

A similar thing happens in a 'marx generater' (whic actually is a problem, it causes misfires of spark gaps).

I'm sure this happens in lightening, but on a vast scale. When streamers make contact, only a little current can flow, but that creates UV, ionizes the air, lowering its resistance, allowing more current to flow......hence the term 'cascade'. Its also why lightening 'flashes'. The same channel of air can conduct several strikes, since the air remains ionized after the main strike (not high temperature plasma, but 'true plasma', which is invisible).

Anyway, I'm sorry if it seems like I'm ranting, but thats my theory, criticisms are more than welcome.
 

yes lighting emits AM amplitude modulation

when the inital leader builds up there is an increase in backgroud noise
then you get the strike and this 'carrier' increases in amplitude
then decreases as the voltage potential discharges


however to be sure get an am meter and connect it to an antenna or long wire {use the appropriate safety circuits}

then you can tune to a specific frequency lower than 1mhz and watch it

i read an article in epe magazine and the guy had designed a circuit for this very purpose

i beleve it was 2000 or 2001 ill look back find it and post somemore details


if a body emits an rf signal that increases in amplitude then decreases
yes this is am

modulation occurs when you have several sheet lightning combine to form a bolt

as for fork lightning yes this also would combine to form am

or atleast a modulated amplitude

modulation is by difinition an envilope carried by a signal

i think this is easily measured

what about FM

wideband em maybe not


as a point to note

rf isnt an em signal it is a modulation of the earths magnetic field
using an em source
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top