Hello Stefan,
I will save a copy of the
http://www.webalice.it/rromero/live_cumiana/last-LFtest_2970.jpg trace, I think
it is particularly valuable.
The frequency spreading to which you called attention is quite interesting.
I hadn’t recalled any mention of frequency spreading in geomagnetic storms in
the VLF literature, so I looked through some papers and was surprised to find:
spectra and power spectral densities of amplitude modulation of VLF signals
caused by a geomagnetic storm (modulation frequency range 0.00Hz through
0.03Hz). The plots are very interesting; I will send them in a separate message
right after this message.
The plots are from "Subionospheric VLF measurements of the effects of
geomagnetic storms on the mid-latitude D-region", Inan 2005
(http://vlf.stanford.edu/sites/default/files/publications/2005-06.pdf ) (Figure
5, page 4)
You mentioned amplitude enhancement: I think that in geomagnetic storms
amplitude reduction is more often reported, but that is based on VLF studies.
At 2970 Hz amplitude enhancement from multimode-null shifting in a geomagnetic
storm is probably far more likely than at VLF frequencies. Based on simulations
(take with large grain of salt) it seems like multimode enhancement of 2970 Hz
signals on 300km to 1000 km paths during ionospheric disturbances in general
is not unlikely. I would not be surprised to see path-specific enhancement at
2970 Hz during disturbances.
Regarding phase shift (in case it is relevant to stacking that Paul is doing):
I roughly estimated the K index for March 21-23 flux variations at Wingst and
Niemegk and came up with a guess of K = 6.
The first example phase vs. K-index-level example that I found in the
literature* cited a case with K=7, and showed (for cases described as similar)
exaggerated advance and retardation over the diurnal with a phase swing
equivalent to 1.7 cycles at 16kHz (106 us); this was for a path in which the
undisturbed diurnal swing was 0.25 cycles (16 us).
It would be a big stretch to assume any close correspondence between the
Burgess* study and the March 21-23 2970 Hz signals, but perhaps the Burgess
results can be viewed as a potential future reference point.
* "Propagation of VLF Waves Under Disturbed Conditions" - Burgess 1964 (
http://nvlpubs.nist.gov/nistpubs/jres/68D/jresv68Dn1p115_A1b.pdf )
I will save all of the above information including the trace from IK1QFK and
the Wingst and Niemegk data, because I am guessing that you and those who have
taken the time and effort to record your signal may have collected the first
geomagnetic storm data in the virtually unexplored 2kHz - 4kHz, 500km - 1000km
range.
73,
Jim AA5BW
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of DK7FC
Sent: Friday, March 24, 2017 5:49 PM
To: [email protected]
Subject: Re: ULF: New carrier near 2970 Hz...
Hi Jim, ULF,
i wondered why the trace at IK1QFK in 5 wavelengths distance becaome so blurry
in the recent days.
See http://www.webalice.it/rromero/live_cumiana/last-LFtest_2970.jpg and use a
zoom function :-) The SNR of the next upper bin (5.06 uHz
'higher') reached the same levels and sometimes even more! The overall SNR was
increased significantly, to up to 14 dB.
Could this have to do with enhanced sky-wave propagation? During the same time
the signal became smaller at Paul's location...
I'm looking forward to the new VLF/ULF grabber at DL0AO, the are having
progress in beg steps! Impressive.
It will certainly help to permanently inspect the signal out of different
locations...
73, Stefan
Am 23.03.2017 22:52, schrieb [email protected]:
> Geomagnetic K-index elevated March 21 through March 23, approximately 3<
> Kp< 4 but higher in Europe with levels at Wingst and Niemegk varying by 50nT
> to 80nT at times during that period.
>
> Mentioning this in case it applies to received phase of the 2970 signal.
>
> But now wondering if this disturbance should be thought of as cause or
> effect, with 2970 TX currents having grown to 180 mA.
>
> Jim AA5BW
>
>
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of DK7FC
> Sent: Wednesday, March 22, 2017 9:15 AM
> To: [email protected]
> Subject: Re: ULF: New carrier near 2970 Hz...
>
> Hi Paul,
>
> Interesting. Do you also use the noise normalisation function which proved to
> be useful in recent stackings on 5170 Hz?
>
> Still a few weeks before the 6 channel input soundcard for the Raspi
> appears...
>
> 73, Stefan
>
> Am 22.03.2017 11:25, schrieb Paul Nicholson:
>
>> Stefan wrote:
>>
>>
>>> Isn't it extremely unlikely that this is something elso than my
>>> signal??
>>>
>> Well I don't know. It would be an extraordinary achievement for your
>> 2970 signal to reach this far. It needs a result
>> that can stand up to scrutiny. I'd like to do some more
>> work with it to get an unequivocal detection at 5 sigma.
>>
>>
>>> I'm going to run the carrier another few days, at least until
>>> friday,
>>>
>> A few more days signal will help. Adding 21st didn't
>> improve the peak, nor did the blanker settings I left running last
>> night.
>>
>> For these runs I am blanking each antenna channel independently, then
>> mixing and phasing. Usually I do the mixing first and blank the
>> composite signal.
>> While one channel is blanked and another isn't, the mix is wrong.
>> That ought to be worse than blanking after the mix. With less than
>> 5% blanking factor it might not be much of an issue either way.
>>
>> I can also look again at your previous 2970 tests, stacking the same
>> 14:00 to 19:00 window.
>>
>> --
>> Paul Nicholson
>> --
>>
>>
>
>
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