On Thu, 07 Aug 2008 06:44:00 -0400, Randy Yates <yates@ieee.org> wrote:>Eric Jacobsen <eric.jacobsen@ieee.org> writes: >> [...] >> So there are, IMHO, two major things at work 1) Impulsive waveforms >> have broad power spectra, 2) There's a LOT of energy in a lightning >> strike. > >God's impulse radio??? :)If we could just figure out the code... ;) Eric Jacobsen Minister of Algorithms Abineau Communications http://www.ericjacobsen.org Blog: http://www.dsprelated.com/blogs-1/hf/Eric_Jacobsen.php
Lightning and Fourier transform of an impulse
Started by ●August 5, 2008
Reply by ●August 7, 20082008-08-07
Reply by ●August 7, 20082008-08-07
"Randy Yates" <yates@ieee.org> wrote in message news:m3myjprtov.fsf@ieee.org...> Eric Jacobsen <eric.jacobsen@ieee.org> writes: >> [...] >> So there are, IMHO, two major things at work 1) Impulsive waveforms >> have broad power spectra, 2) There's a LOT of energy in a lightning >> strike. > > God's impulse radio??? :)Oh, please! He of Infinite Complexity inventing flagellated bacterium on the one hand, and then using a spark gap transmitter on the other? Doesn't wash!
Reply by ●August 7, 20082008-08-07
"MikeWhy" <boat042-nospam@yahoo.com> wrote in message news:xiFmk.32774$co7.2251@nlpi066.nbdc.sbc.com...> "Randy Yates" <yates@ieee.org> wrote in message > news:m3myjprtov.fsf@ieee.org... >> Eric Jacobsen <eric.jacobsen@ieee.org> writes: >>> [...] >>> So there are, IMHO, two major things at work 1) Impulsive waveforms >>> have broad power spectra, 2) There's a LOT of energy in a lightning >>> strike. >> >> God's impulse radio??? :) > > Oh, please! He of Infinite Complexity inventing flagellated bacterium on > the one hand, and then using a spark gap transmitter on the other? Doesn't > wash!Doh, wait! What could I have been thinking? Nothing else would have sufficient bandwidth. Of course it looks like white noise to the undeserving. But then, it could be just a random, simple, meaningless physical phenomenon...
Reply by ●August 7, 20082008-08-07
On Aug 6, 5:21 pm, Jerry Avins <j...@ieee.org> wrote:> The lightning isn't really an impulse. Some have durations of > milliseconds, few less than tens of microseconds. That's more than > enough to localize the interference in time.An impulse in the time domain is by definition localized in time. As are a closely spaced complementary pair of delta functions comprising a short pulse. The problem is that sums of purely imaginary exponentials are a lousy way of representing the time at which impulsive or merely abrupt things occurred. Or to put it bluntly, the frequency domain is practically speaking a bad way to represent one-shot or random (non-periodic) events.
Reply by ●August 8, 20082008-08-08
On Aug 6, 10:21�pm, Jerry Avins <j...@ieee.org> wrote:> Chris Bore wrote: > > But the frequency spectrum exists over all time, not just during the > > impulse. > > > So I don't think this can be used to explain why the lightning > > disrupts radio for a short time. > > Chris, > > The lightning isn't really an impulse. Some have durations of > milliseconds, few less than tens of microseconds. That's more than > enough to localize the interference in time. > > � �... > > Jerry > -- > Engineering is the art of making what you want from things you can get. > �����������������������������������������������������������������������Jerry, I agree but.. Frequency, as defined by a Fourier Transform, is a steady state frequency spectrum whose components exist at fixed amplitude over all time. So the Prof can't use the broadband nature of the frequency spectrum to explain a time-limited event. He is mixing orthogonal domains. He can say the spectrum is broadband. But he can't say the spectrum is somehow broadband for a short time. I think the Prof should have accepted that lightning interferes because it is a bloody great spark, and left it at that. Chris ================ Chris Bore BORES Signal Processing www.bores.com
Reply by ●August 8, 20082008-08-08
Chris Bore wrote:> On Aug 6, 10:21 pm, Jerry Avins <j...@ieee.org> wrote: >> Chris Bore wrote: >>> But the frequency spectrum exists over all time, not just during the >>> impulse. >>> So I don't think this can be used to explain why the lightning >>> disrupts radio for a short time. >> Chris, >> >> The lightning isn't really an impulse. Some have durations of >> milliseconds, few less than tens of microseconds. That's more than >> enough to localize the interference in time. >> >> ... >> >> Jerry >> -- >> Engineering is the art of making what you want from things you can get. >> ����������������������������������������������������������������������� > > Jerry, > > I agree but.. > > Frequency, as defined by a Fourier Transform, is a steady state > frequency spectrum whose components exist at fixed amplitude over all > time. > > So the Prof can't use the broadband nature of the frequency spectrum > to explain a time-limited event. He is mixing orthogonal domains. > > He can say the spectrum is broadband. But he can't say the spectrum is > somehow broadband for a short time. > > I think the Prof should have accepted that lightning interferes > because it is a bloody great spark, and left it at that. > > Chris > ================ > Chris Bore > BORES Signal Processing > www.bores.comAn impulse creates all frequencies, and they exist for all time. The interference caused by lightning is brief, showing that lightning isn't a true impulse. All well and good, but we knew that all along, didn't we? If you like, think of a lightning stroke as abrupt keying, producing lots of splatter. We've all heard the splatter from an SCR motor controller excited at the mains rate extending well up into the AM broadcast spectrum. Long ago, listening to the FM tuner I had built with less-than-perfect limiters, I heard a noise like !!!!!!! !!!!!!! !!!!!!! and ran out to the street shouting, "Dad! It's misfiring on one cylinder!" Quasi-impulses make splatter that is only quasi-eternal. :-) Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●August 8, 20082008-08-08
Chris Bore wrote:> On Aug 6, 10:21 pm, Jerry Avins <j...@ieee.org> wrote: >> Chris Bore wrote: >>> But the frequency spectrum exists over all time, not just during the >>> impulse. >>> So I don't think this can be used to explain why the lightning >>> disrupts radio for a short time. >> Chris, >> >> The lightning isn't really an impulse. Some have durations of >> milliseconds, few less than tens of microseconds. That's more than >> enough to localize the interference in time. >> >> ... >> >> Jerry >> -- >> Engineering is the art of making what you want from things you can get. >> ����������������������������������������������������������������������� > > Jerry, > > I agree but.. > > Frequency, as defined by a Fourier Transform, is a steady state > frequency spectrum whose components exist at fixed amplitude over all > time. > > So the Prof can't use the broadband nature of the frequency spectrum > to explain a time-limited event. He is mixing orthogonal domains. > > He can say the spectrum is broadband. But he can't say the spectrum is > somehow broadband for a short time. > > I think the Prof should have accepted that lightning interferes > because it is a bloody great spark, and left it at that. > > Chris > ================ > Chris Bore > BORES Signal Processing > www.bores.comAn impulse creates all frequencies, and they exist for all time. The interference caused by lightning is brief, showing that lightning isn't a true impulse. All well and good, but we knew that all along, didn't we? If you like, think of a lightning stroke as abrupt keying, producing lots of splatter. We've all heard the splatter from an SCR motor controller excited at the mains rate extending well up into the AM broadcast spectrum. Long ago, listening to the FM tuner I had built with less-than-perfect limiters, I heard a noise like !!!!!!! !!!!!!! !!!!!!! and ran out to the street shouting, "Dad! It's misfiring on one cylinder!" Quasi-impulses make splatter that is only quasi-eternal. :-) Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●August 8, 20082008-08-08
Chris Bore wrote:> On Aug 6, 10:21 pm, Jerry Avins <j...@ieee.org> wrote: >> Chris Bore wrote: >>> But the frequency spectrum exists over all time, not just during the >>> impulse. >>> So I don't think this can be used to explain why the lightning >>> disrupts radio for a short time. >> Chris, >> >> The lightning isn't really an impulse. Some have durations of >> milliseconds, few less than tens of microseconds. That's more than >> enough to localize the interference in time. >> >> ... >> >> Jerry >> -- >> Engineering is the art of making what you want from things you can get. >> ����������������������������������������������������������������������� > > Jerry, > > I agree but.. > > Frequency, as defined by a Fourier Transform, is a steady state > frequency spectrum whose components exist at fixed amplitude over all > time. > > So the Prof can't use the broadband nature of the frequency spectrum > to explain a time-limited event. He is mixing orthogonal domains. > > He can say the spectrum is broadband. But he can't say the spectrum is > somehow broadband for a short time. > > I think the Prof should have accepted that lightning interferes > because it is a bloody great spark, and left it at that. > > Chris > ===============> Chris Bore > BORES Signal Processing > www.bores.comAn impulse creates all frequencies, and they exist for all time. The interference caused by lightning is brief, showing that lightning isn't a true impulse. All well and good, but we knew that all along, didn't we? If you like, think of a lightning stroke as abrupt keying, producing lots of splatter. We've all heard the splatter from an SCR motor controller excited at the mains rate extending well up into the AM broadcast spectrum. Long ago, listening to the FM tuner I had built with less-than-perfect limiters, I heard a noise like !!!!!!! !!!!!!! !!!!!!! and ran out to the street shouting, "Dad! It's misfiring on one cylinder!" Quasi-impulses make splatter that is only quasi-eternal. :-) Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●August 8, 20082008-08-08
Chris Bore wrote:> On Aug 6, 10:21 pm, Jerry Avins <j...@ieee.org> wrote: >> Chris Bore wrote: >>> But the frequency spectrum exists over all time, not just during the >>> impulse. >>> So I don't think this can be used to explain why the lightning >>> disrupts radio for a short time. >> Chris, >> >> The lightning isn't really an impulse. Some have durations of >> milliseconds, few less than tens of microseconds. That's more than >> enough to localize the interference in time. >> >> ... >> >> Jerry >> -- >> Engineering is the art of making what you want from things you can get. >> ����������������������������������������������������������������������� > > Jerry, > > I agree but.. > > Frequency, as defined by a Fourier Transform, is a steady state > frequency spectrum whose components exist at fixed amplitude over all > time. > > So the Prof can't use the broadband nature of the frequency spectrum > to explain a time-limited event. He is mixing orthogonal domains. > > He can say the spectrum is broadband. But he can't say the spectrum is > somehow broadband for a short time. > > I think the Prof should have accepted that lightning interferes > because it is a bloody great spark, and left it at that. > > Chris > ================ > Chris Bore > BORES Signal Processing > www.bores.comAn impulse creates all frequencies, and they exist for all time. The interference caused by lightning is brief, showing that lightning isn't a true impulse. All well and good, but we knew that all along, didn't we? If you like, think of a lightning stroke as abrupt keying, producing lots of splatter. We've all heard the splatter from an SCR motor controller excited at the mains rate extending well up into the AM broadcast spectrum. Long ago, listening to the FM tuner I had built with less-than-perfect limiters, I heard a noise like !!!!!!! !!!!!!! !!!!!!! and ran out to the street shouting, "Dad! It's misfiring on one cylinder!" Quasi-impulses make splatter that is only quasi-eternal. :-) Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●August 8, 20082008-08-08
Chris Bore wrote:> On Aug 6, 10:21 pm, Jerry Avins <j...@ieee.org> wrote: >> Chris Bore wrote: >>> But the frequency spectrum exists over all time, not just during the >>> impulse. >>> So I don't think this can be used to explain why the lightning >>> disrupts radio for a short time. >> Chris, >> >> The lightning isn't really an impulse. Some have durations of >> milliseconds, few less than tens of microseconds. That's more than >> enough to localize the interference in time. >> >> ... >> >> Jerry >> -- >> Engineering is the art of making what you want from things you can get. >> ����������������������������������������������������������������������� > > Jerry, > > I agree but.. > > Frequency, as defined by a Fourier Transform, is a steady state > frequency spectrum whose components exist at fixed amplitude over all > time. > > So the Prof can't use the broadband nature of the frequency spectrum > to explain a time-limited event. He is mixing orthogonal domains. > > He can say the spectrum is broadband. But he can't say the spectrum is > somehow broadband for a short time. > > I think the Prof should have accepted that lightning interferes > because it is a bloody great spark, and left it at that. > > Chris > ================ > Chris Bore > BORES Signal Processing > www.bores.comAn impulse creates all frequencies, and they exist for all time. The interference caused by lightning is brief, showing that lightning isn't a true impulse. All well and good, but we knew that all along, didn't we? If you like, think of a lightning stroke as abrupt keying, producing lots of splatter. We've all heard the splatter from an SCR motor controller excited at the mains rate extending well up into the AM broadcast spectrum. Long ago, listening to the FM tuner I had built with less-than-perfect limiters, I heard a noise like !!!!!!! !!!!!!! !!!!!!! and ran out to the street shouting, "Dad! It's misfiring on one cylinder!" Quasi-impulses make splatter that is only quasi-eternal. :-) Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
