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Date: Sat, 04 Feb 2017 19:31:33 +0100
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Subject: Re: ULF: EbNaut over 3 wavelengths on ULF
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Jim,

i assume your plots refer to a constant ERP. Could you scale the plot to 
a constant antenna current?  A range of 0.1...10 kHz is fine. That could 
be helpful to better understand what could be possible on which band...
Most VLF TX systems are current or even voltage limited....

73, Stefan

Am 03.02.2017 13:51, schrieb hvanesce@comcast.net:
> Stefan and Paul,
>
> Attached is a 2nd-pass FDTD plot (E-field only); theoretically more accurate with some small corrections and refinements.
>
> The attached plot and the two FDTD plots sent yesterday represent daytime propagation over a conductive ground similar to sea water, for comparison with the NAVALEX plot (daytime, sea water)
>
> The NAVELEX plot suggests:  ~ 3dB more signal at 2.9kHz than at 5.17 kHz (880 km)
> The FDTD plot suggests:              far less signal at 2.9 kHz than at 5.17 kHz (880 km)
>
> A benefit of FDTD analysis is inclusion of all modes, including evanescent.
>
> Given very limited experimental validation of propagation computational tools between 2kHz and 4kHz at distances between 100 km and 1000 km, your ULF tests may show strengths and weaknesses in the computational tools.
>
> 73,
>
> Jim  AA5BW
>
>
>
> -----Original Message-----
> From: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of hvanesce@comcast.net
> Sent: Thursday, February 2, 2017 3:27 PM
> To: rsgb_lf_group@blacksheep.org
> Subject: RE: ULF: EbNaut over 3 wavelengths on ULF
>
> Stefan and Paul,
>
> I've been unable to find any empirical validation of LWPC fidelity below 5kHz.
>
> Attached is a preliminary pass (E and B field amplitude vs frequency and distance) with FDTD, showing some deep nulls at frequencies and distances of interest.
>
> (compare with NAVELEX 0101 113 plot annotated by Stefan https://dl.dropboxusercontent.com/u/19882028/VLF/fig_02_25a.png ) The NAVALEX plot is based on an algebraic approximation [details shown in the NAVELEX document, summary of those details (and link to document), in this thread ~ 02:17, January 8, 2017]
>
> Empirical validation of FDTD in the 2kHz to 4kHz range is lacking but FDTD can provide good accuracy at high resolution (in f, d, E and B) given accurate h' and beta values.
> The h' and beta values used for the attached FDTD plots are nominal daytime values; no telling how different the result might be for actual h' and beta during your recent tests.
> On the other hand, the depth and sharpness of the nulls shown in the FDTD plots might well be relevant.
>
> I don’t know the attachment file size limit, so in case the limit is 100 kB or less, I will send "FDTD Plot 2 of 2  (B field)" in a message immediately following this message.
>
> 73,
>
> Jim AA5BW
>
>
>
>
> -----Original Message-----
> From: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Paul Nicholson
> Sent: Sunday, January 29, 2017 12:26 PM
> To: rsgb_lf_group@blacksheep.org
> Subject: Re: ULF: EbNaut over 3 wavelengths on ULF
>
>
> Jim wrote:
>
>   >  Excellent diagnostic method and implementation.
>
> The method has some weaknesses Jim but in the absence of any artificial signals it's the best I can do.  I must repeat the exercise when we next get a thunderstorm nearer to Heidelberg.  Looking at the spectrum of the sferics will reveal if we have some ground/sky wave cancellation at that frequency and range.
>
> Stefan wrote:
>
>   >   From the known decoded EbNaut messages, what was the SNR at>  Renato or on your side?
>
> Nothing detectable here or at Cumiana so I can't answer the question of how many days need stacking.  Until there is some glimpse of a signal, it is completely unknown.  I can only estimate a lower limit.
>
> With your estimated ERP I think something should be detectable in one day or two.  But stacking two days of your recent carrier shows nothing.  Even with my more conservative ERP estimate I would expect to see something of your signal.
>
> Between 2016-06-26 13:00 and 2016-07-31 08:00 you transmitted carrier with 30mA antenna current.  I received and stacked over 34 days of carrier (about 15dB stacking gain) with no sign of signal.  You estimated 100nW ERP.
>
> Now you can do 150mA current - about 14dB gain over July's signal.  Plus, improvements here to filtering and blanking may add 2 or 3dB more.
>
> We can in two days exceed the stacked signal for the whole of July.  Also with your higher ERP I can see the signal each day at Bielefeld to check the phase.
>
> I think we should try some daytime carrier repeats.  Already we know there is nothing after 2 days so we will need at least
> 4 days to get a hint of signal and then at least 10 days to collect enough signal for some measurements.  It is surely certain that we will eventually pick up the signal after enough days.
>
> I'm thinking about shutting down my workstation to install an extra scratch disk which will speed up the signal search.
> It's been busy for 137 days so no chance to close it down.
> There are still 154 jobs running though.
>
> --
> Paul Nicholson
> --
>