Hello Stefan,
Congratulations on your first capture of signals from the new 970 Hz setup.
Some observations regarding operation at 970Hz, 2.97kHz, 5.17kHz and 6.47kHz
are attached.
Summary: the results are preliminary (additional validation in progress), but
correlation between experiments by yourself and Paul, and the attached
analysis, is sufficient to mention the following:
0.97kHz at 880km at 0.3uW (30kV) looks as good as 6.47kHz at 880km at 1.0uW
(ref November 17-18 2016, the results of which agree with the attached analysis)
0.97kHz at 880km at 0.3uW (30kV) looks ~ 5dB better than the analytical
estimate (attached) of 2.97kHz at 880km at 1.2uW (ref December 6-17 2016)
Challenges at 2.97 kHz:
Based on the attached analysis, derived from the document that you posted last
week, and validated using results of 5.17kHz and 6.47kHz tests by yourself and
Paul (fairly good agreement between attached analytical solution for SNR and
your experimental results); and also loosely/qualitatively supported using
results of your 2.97kHz test, it appears that:
a) The deep null with minimum between 3kHz and 4kHz (depending on time of
day and earth conductivity) shown in Figure 2-25 is quantitatively and
qualitatively realistic
b) Natural noise is not attenuated as much as signal in the null described
above
c) At the 2.97kHz (December test) field strengths estimated in the
attached analysis, the signal level could have been close enough to the
receiver-noise/cultural-noise floor to negate some of the potential advantage
of noise diminishing with signal in the 3kHz null (in other words, the 3kHz
null could have comprised a double hit to SNR: (1) a propagation advantage for
noise vs. signal in the null, and (2) receiver-noise/cultural-noise negation of
some part of the fractional tracking of noise with signal in the null
d) 0.3uW (30kV) at 970 Hz looks as good as 1.0uW at 6.47kHz (ref November
17-18 2016 experimental results with which the attached analysis agrees)
970 Hz vs. 5.17kHz or 6.47kHz:
a) 970 Hz predicted SNR at 0.3uW is roughly equivalent to 6.47kHz SNR at
1.0uW
b) 970 Hz propagation (phase and amplitude) could be significantly more
stable (over day, night, and ionospheric conditions) than propagation at
5kHz-30kHz
970 Hz links could (at distances over 200km and especially at distances over
500km) work comparatively well with: receivers in some indoor environments,
receivers in vehicles (engine off) and receivers in urban areas (970Hz QTEM
wave less affected by infrastructure and structural materials) (indoors and in
urban centers a good analog high-pass filter at 300Hz and a well-shielded RX
loop would help)
c) 970 Hz links with 5dB margin or so should work underwater, and fairly
deep underground
d) Possible advantages in hilly and wooded terrain
e) It might be very difficult to explore these interesting properties (b,
c, d and e above) in the far field, at any other frequency:
Example: 7dB loss deep underground at 970Hz translates to 400dB loss at 6kHz;
frequencies between 2kHz and 4.5kHz would not be appropriate for (b, c, d and e
above); and at frequencies below 500Hz it would be difficult (not impossible
but at the very least a lot of work) to have SNR margin in the far field from a
practical transmitter; line harmonics and various 1/f noises become
significant; and low data rates diminish the efficiency of testing.
The 1kHz realm has its own set of propagation, E/M field and equipment
particularities, meaning a bit of uncertainty and/or effort along the way. The
paragraphs above highlight the potential advantages of 1kHz; they are somewhat
unique.
The attached analysis is not user friendly, it is basically a scratchpad; but I
can clean it up and add plots if that would help in any way. Most of the
document consists of cut/paste modifications of a basic 5-line solution, plus a
section (first page) in which input parameters are documented. The whole
analysis is basically one equation (repeated three times on page 2 for example)
with a number of units conversions, plus input-parameter documentation; but it
faithfully reproduces the NAVELEX plots, and the data in those plots agree
fairly well with the 3kHz – 6.4kHz experiments. I can clean it up, condense it
and add plots if anyone is interested. The most important addition would be a
table of attenuation parameters manually extracted from Fig 2-20, with
interpolation to synthesize daytime-land attenuation factors. Fig 2-20 provides
input data for Fig 2-21, 2-22, 2-23, 2-24 and 2-25.
P.S. I'm sending this with just 1 of 5 attachments because the first send
attempt appears to have failed (attachments are ~75kB each, total 380kB).
73,
Jim AA5BW
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of DK7FC
Sent: Tuesday, January 10, 2017 4:43 PM
To: [email protected]
Subject: ULF: A first local test on 970 Hz / 309 km
Hi ULF,
Since a few hours i'm running 15 mA antenna current on 970 Hz, the 309 km band.
This requires to apply 5 kV to the antenna. You can see a very faint trace on
the lower image at
http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html
Just about 10 dB SNR in 424 uHz in 3.5 km distance, or in 0.011 lambda
distance. The receive antenna is a H field antenna that is not even pointing to
the transmitter. Also the preamp noise is dominating the background noise on
that frequency. So the RX is deaf on that band.
Anyway, there is something.
The ALC into SpecLab does a very good job, it holds the antenna current stable
during all the changes and working point drifts. The plot can be seen at
http://www.iup.uni-heidelberg.de/schaefer_vlf/VLF/TX.png
15 mA results in an ERP of 3 nW.
My new preamp circuit is waiting for a first test together with the large loop.
I hope to pick up the signal in at least 5 km distance with that preamp which
is really low noise down to the lower Hz range.
An E field reeiver would be a better choise for the reception from that E field
Tx antenna, at least in the lower near field. Maybe that will give another test
then.
With 30 kV i could reach 0.3 uW. Not sure where this could be detected?
And who knows the advantages of this part of the spectrum for our purposes!?!
Since 21:20 UTC, a 2 character EbNaut message is running. It will take 2h,
2min, 40s. Hopefully the tree grabber is available until the message ends. It
will shut down in a few hours due to lack of solar energy in these days (an
improvement of this system has already been prepared and waits for the
installation).
73, Stefan
|
