Lightning oscillations

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>the dominent frequency in this waveguide is 10-11kHz.

Very interesting, and complicated, like nature always is.
I have to use the LP filter because the noise at 65 and 80 kHz makes my station nearly unusable. I know it introduces a delay also.
Is there any reason to otherwise keep the pass band as high as possible? I have other noises at 20 kHz but not too bad, but I kept lowering the cut-off even down to 14 kHz. That is why my wave looks so smooth.
I did notice a few weeks ago that close lightning from the Norway coast looked different. Now it makes sense that the wave is altered on the way to Finland from Pakistan for example.
Jim

 

Jim, a couple of years ago, I started a 'primer' document... never pursued it, but I'll share it here, attached...
It tries to be very basic...   I approached it in the "BONES' rationalization, as: "I'm an Operator, Jim! Not a Physicist"...

It speaks of the "Ground Wave" and the "Sky Wave" for simplicity, but there are actually 3 components of interest,...
the "Ground Wave" from a source follows terrain, and depending on geology, geography, etc, can travel sometimes  a bit further than its associated "Space Wave" (Don't confuse with "Sky Wave"... they're different).

The 'second' component of the Ground Wave terminology is  a direct signal straight line from Source called the "Space Wave"... directly in the 'airspace" between the source and the detector. Reception depends on altitude, among other things, of the source, and receiving antenna...
so when the 'horizon' is reached, it's a rare part of the "Space Wave" signal that reaches you, although the 'ground wave component' may be available at a bit more distance.The effective reception distance from source for ground wave components is maybe 80km / 50mi/.
The only expected delay is pure travel time at the speed of light, from the source, + any delays in antennas or receiver processing.

Beyond that distance limit for "Best" groundwave reception, we're detecting 'skywaves'... those that reflect between the earth and the ionosphere,... and here this can be la-la land in terms of frequency spectrum of the impulse, distortion,Time of Arrival, etc  Most affected portions of the impulse are the higher frequencies, which don't bounce as well, but the lower frequencies can 'ring' and bounce through the waveguide. The time the signal reaches an antenna depends on the number of bounces, therefore greater distance traveled. And that 'bounce' depends on terrain, height of various levels of the ionosphere which fluctuate both in particle/charge content and it's altitude especially from day to night. This is called the "Earth-Ionospher Waveguide".
And both the Earth side and Ionosphere side of the waveguide only tend to bounce the 'lower' frequency components....

So, as Richo mentioned, we're getting most energy for those skywaves at around 10-11 kHz (There is at least one researcher who after years of collecting data, suggests the 'median' is right at 13 kHz) Whatever.

So as illustrated in your signal image, (and in one of the diagrams in the attached) you have a great 'Mexican hat' caused by 'skywave' capture
... which include little or NONE of the precharge, initial charging and discharge stroke frequencies (Higher), but only multiple 'skywave' signals.... of much lower frequencies.

One way to tell,


You might note that nearby Low Frequency sources, specifically those that generate a 'radio' signal are consistent in
cycle repetition, and don't typically have the 'delay' accumulation noted in sferic impulses at distance.

So... receiving low end frequencies only, if you have to filter, ain't bad... you're still 'detecting' them .!  Nearby cells have
a much stronger 'higher frequency' energy component, and there are uses for that higher frequency data... Blitzortung
has dreams for that data down the road, but none of that matters if the network cannot detect a signal.  So, as a
'single' station might have to operate low end, you still detect, and enable location... The other stations without the issues in
the higher frequencies can contribute that additional data... they might not be able to unless you assist with location! 
It's a TEAM Effort!

OH... by the way... the server knows how much time delay is designed into your system, the expected time delays of the filters,
antenna type, etc.. if you've configured correctly, and entered the correct data on your station page at BT...
...so it knows what to expect,and it takes all that into account when processing. So if folks diddle around with 'redesign', strange antennas, other stuff, it can mess things up.

Cheers!
Mike