- Walter, Take a series coupling capacitor connected to a resistor going to ground with an amplifier of some sort connected at the junction. Hit that networkMessage 1 of 5 , Apr 1, 2005View SourceWalter,
Take a series coupling capacitor connected to a resistor going to
ground with an amplifier of some sort connected at the junction. Hit
that network with a single finite impulse and you will see exactly that
kind of waveform. The decay time is the product of the RC time constant.
--- In VLF_Group@yahoogroups.com, "karula4711" <fedderwi@u...> wrote:
> Hi group,
> I'm trying to identify the sharp impulse to the right,
> please have a look at
> Thanks, Walter
- Hi Bear, you ve been too long in ulfelf :-) yes, you re right, it looks like a RC decay after some short pulse. But this does not explain the origin of thisMessage 2 of 5 , Apr 1, 2005View SourceHi Bear,
you've been too long in ulfelf :-)
yes, you're right, it looks like a RC decay after some short pulse.
But this does not explain the origin of this pulse as such.
There are none of these if I run the receiver without antenna.
So somehow it's picked up from there. I'll test different locations
and see if it's only on Rabbits hill. I suspect the wind energy
converters. Theres a whole farm of it and the closest is about half a
mile (whatever mile you like - some 700 - 800 m) away.
I can't test at the workbench cause everything sinks into hum. I've
only 10 Megohm of input impedance but's sufficient to grep all the
noise in the house. It even partially passes the elf test: waving a
sheet of plastic in the vicinity of the antenna jack is clearly
No, my name is not Lambert, and the antenna is an aluminium pipe,
2m long, and I can compute the spectrum even of these short pulses *)
*) this is meaningful only for readers of ulfelf!
- Hi, it is the impulse noise of wind energy converters. see here: http://www.fbw.hs-bremen.de/~olbers/gtx1.htm WalterMessage 3 of 5 , Apr 1, 2005View SourceHi,
it is the impulse noise of wind energy converters.
- Hi Walter, All, ... The spike on the right is very different to a sferic and looks a lot like local impulsive noise. As Bear said, it s a nice cleanMessage 4 of 5 , Apr 1, 2005View SourceHi Walter, All,
lot like local impulsive noise. As Bear said, it's a nice clean
exponential RC type decay. These are typical of the bassy thumps
and clicks that you hear when electrical equipment is turned on
or the pulses from a very close impulse source such as an electric
fence. The dominant frequency components are low, less than 1kHz
By contrast, the sferic has a lot of higher frequency content and
the waveform has several zero crossings, this is a very typical
weak sferic. It will have passed some way through the earth-
ionosphere duct, so its spectrum is enhanced at some frequencies
and cancelled at others. The result is the somewhat rounded beat
envelope that you have on the left.
> Or is this how relatively close lightning strokesNearby lightning strokes give a very strong, very long and
> look like?
complicated signal with lots of structure. They often continue
for well over a second, with a tail consisting of all sorts of
funny hisses and fizzling noises. With sufficient attentuation,
they would probably resemble the decaying 'thump' on the right
more than the sferic on the left as you would be picking up the
near field of the discharge and you'll get all the low frequency
components before they're filtered by the earth-ionosphere duct.
With the receiver at normal gain, it's difficult to make sense
of the signal from nearby lightning. The receiver clips, filters
ring like crazy and the whole thing is a mess.
BTW, I checked more closely that that double whistler from the other
day - it's not the same one I recorded. Although the whistler
timing is very similar, the pattern of accompanying sferics does
PS, I wrote the above earlier. Just received Walter's latest
post with the solution. Thanks for the mp3 - you can hear
the thing turning very nicely!
Thank you for the interesting posts and questions, Walter,
keep them coming!