Paul,
Thanks for your reply below. In available time I'm trying to verify that FDTD
can be helpful for the ULF tests (and vice versa, that the ULF experimental
results can validate FDTD for ULF). So far I've found three positive
indicators based on Stefan's tests at 2.97 kHz. One indicator is correlation of
(a) extrapolated signal strength Cumiana/Todmorden, adjusted for antenna
current (and including error margin for estimated sensitivity at Cumiana), with
(b) the FDTD characteristics in the attached. For that purpose (particularly
for comparing signal strengths extrapolated from SNR at known integration time
and estimated receiver sensitivity), should I consider the effective
integration time of your 9-day stack of 11-hour segments to be 356400 seconds
i.e. bandwidth 2.8 uHz?
Thanks,
Jim AA5BW
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Paul Nicholson
Sent: Monday, March 27, 2017 3:54 PM
To: [email protected]
Subject: Re: LF: DK7FC in Todmorden at 2970 Hz
Jim wrote:
> I’m not sure if Paul’s stacking process is more > akin to coherent
> integration of the time-domain data
It is. I'm simply adding the daily signals in the time domain. A box car
averaging with a repetition period of 24 hours. The signal (hopefully) adds
coherently to sum to 9 times the average amplitude of the received signal. For
the plots, I divide by nine (and by the average normalisation factor) to give a
y axis scale representing the average received signal strength.
The signal doesn't integrate so well if I just do a single 9 day integration
(actually 817200 seconds which is 2017-03-11_13:00 to 2017-03-21_00:00, 9.45
days) in 1.22 uHz bandwidth. For this I extract
13:00 to 00:00 each day, padding the gaps with zeros.
The peak is there but S/N not so good, only about
3 sigma.
I haven't been able yet to get anything out of the four 'unused' days (17th and
21st to 23rd).
> Hard to imagine a tougher frequency range than the > neighborhood of 2970
> Hz.
The average sferic energy is less here, so the sferic blanker is having to do
less work - typically about
5% blanking factor. The threshold doesn't seem
very critical at all. The signal is amidst a forest
of mains harmonics. That's not actually a problem
so long as the rx is impeccably linear and the hum doesn't have too many
sidebands.
Maybe I'm just at an awkward distance where for example ground wave and sky
wave are often cancelling. In one respect the propagation ought to be simpler
- we're below the waveguide cut-off frequency of the higher modes.
One problem I have with the very narrow bandwidths (ie less than say 10uHz) is
numerical noise due to limited floating point precision. This certainly
happens with the Goertzel algorithm of vtnspec and I have to use vtwspec for
the long integrations.
--
Paul Nicholson
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FDTD Plot , updated, (E field).jpg
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