Paul,
Thanks for very good AoA validation of Joe's signal.
Not sure if Joe's antenna is pure vertical and remain intrigued by VLF AoA
error with VLF TX antennas that have non-vertical E components due to (a)
non-vertical slope of TX antenna or (b) infrastructure near TX antenna (or RX
antenna).
I noticed that you used phase with Watson-Watt, and wondered if you used phase
as in attached .png file [which presumes crossed loops and a second antenna
(omni) for blanking to implement unambiguous Watson-Watt solution]; or if you
used phase as part of the time dependent complex amplitude signal of a center
antenna for a four-element (e.g. Adcock) array. [asking because I'm very
unfamiliar with Watson-Watt particulars and have not seen a Watson-Watt
reference to a phase term used with a single (2-element) crossed loop except in
the above/attached context which presumes an omni (2nd antenna, in addition to
crossed loops) for blanking]
The following describes in agonizingly long form why the above question (how
phase is used in your Watson-Watt calculation of the bearing of Joe's signal)
is related to my interest in Stefan's experiments at 970 Hz and 2970 Hz:
In recent spare time I measured VLF phase from distant sources with a rotating
single-axis air-core VLF loop in various proximities to various familiar
infrastructure elements including large/small metal items, vehicles, water,
buried utility conductors, and buildings (interior and exterior), and phase
effects of loop rotation have been small except with unusually close proximity,
and still well-behaved albeit larger phase variation with loop rotation in
unusually close proximity to large/long conductors (for example, vehicles or
very long conductors). These results are (directly or indirectly) not
consistent with reports of large AoA errors with (in some cases)
amplitude-based and (in other cases) phase-sensitive VLF AoA measurements
(including Tkalcevic "...1400 km distant" and Horner "Accuracy of Location of
Sources..."). Tkalcevic makes an interesting case for AoA error given
horizontal components from the VLF TX, and some AoA elevation-angle sensitivity
at the RX is indirectly implied in Tkalcevic and corroborated in a different
context in Horner; but some other examples which include sensitivity of phase
to small changes in loop orientation or loop position leave me wondering about
the RX antenna cables etc. in those high-sensitivity cases, because I haven't
observed much phase sensitivity to small changes in position or orientation of
a single-axis air-core loop.
Much of my interest in the phase aspect of your Watson-Watt AoA measurement of
Joe's signal is related to Stefan's 970 Hz and 2970 Hz experiments, wherein the
high elevation angles of experiments at sub-wavelength distances, and a modal
particularity at 2970 Hz, may exacerbate the effects (on AoA and
near-threshold amplitude) of any horizontal components from the TX antenna. So,
given the good AoA result with your phase-included Watson-Watt calculation of
the bearing of Joe's signal, any basic description (a few words) on how you
used phase would be helpful and appreciated, as it might enlighten potential
phase considerations in Stefan's 970 Hz and 2970 experiments (and AoA in the
6.95 KHz and 8.27 kHz experiments).
Thanks!
Jim AA5BW
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Paul Nicholson
Sent: Monday, May 8, 2017 11:46 AM
To: [email protected]
Subject: Re: LF: NA VLF
Watson-Watt calculation from the antenna amplitudes and phases of the overnight
signal gives 244 degrees which is reasonable given the background noise from
the south west (pulling the apparent bearing southwards from the great circle
280 deg).
Without any calculation, I can see from the relative antenna phases that the
signal is from the west: the E/W H-field is very obviously inverted (relative
to the E-field) from its familiar polarity on European signals.
Joe wrote:
> The carrier was generated with an undisciplined 10 MHz DOCXO > clocking an
> ad9851. As Markus points out, the maths puts it > high by 92.5 uHz.
Overnight signal peaks at 8270.0070625 Hz +/- 0.5 uHz.
Therefore about 3.6 ppb low of the DDS nominal frequency of 8270.0070925...
If I align the FT bins with that frequency, the overnight signal becomes a
sharp line -
http://abelian.org/vlf/tmp/170508e.gif
with a respectable S/N of 13.9 dB in 46.296 uHz.
I'm now confident that this little peak in the spectrum is 10uW from VO1NA.
Distance is 3545 km.
The signal amounts to about 2.6 electrons on the E-field probe.
How's that for a signal report Joe?
Also getting a bit of a signal visible at Forest, Virginia.
Not a very significant peak but it has the same offset.
Only visible on the overnight signal, nothing yet on the daytime. Distance to
Forest is 2442 km so that's very good for a land path.
http://abelian.org/vlf/tmp/170508d.gif
Forest is E-field only so no rejection of the South American nighttime sferics.
--
Paul Nicholson
--
Watson-Watt DF Solution with Correction for ''DF-Solution-Ellipticity g....png
Description: PNG image
|
