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 [email protected]:
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: [email protected]
[mailto:[email protected]] On Behalf Of [email protected]
Sent: Thursday, February 2, 2017 3:27 PM
To: [email protected]
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: [email protected]
[mailto:[email protected]] On Behalf Of Paul Nicholson
Sent: Sunday, January 29, 2017 12:26 PM
To: [email protected]
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
--
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