Hello Stefan,
Your data becomes more fascinating with each update. From the .jpg image that
you attached, it seems like the phase changes at the 3.5 km site are not from
SNR and probably not from simple sky/ground-wave interference. If you have
ruled out phase jumps from corona (which I think you did rule out) my next
thoughts would include (among other things) variations in diffraction and/or
re-radiation from local geography and infrastructure, but:
Another thought relates to the above and has me somewhat distracted: if your 65
km results show phase changes larger than SNR-limited phase noise, would that
suggest that you have a practical D-layer bottomside ionosonde?
If your initial SNR measurements at 65 km are representative (first pixels 20dB
at 47 uHz?), it seems like your RX loop orientation and 2970 Hz frequency at 65
km could give D-layer height information at 100 uHz bin width (or at 47uHz over
a two-day period). This is another way of saying that the phase changes that
you see could be related to the ionosphere; but if they are (and it seems like
they have a good chance of being so), they might contain unique information
about local reflection height at ULF, and acquiring local ULF reflection height
from practical equipment (i.e. having a practical D-layer bottomside ionosonde)
would be a unique and valuable achievement. It could for instance be valuable
for your longer-range experiments because it would help to overcome one of the
biggest limitations of LWPC (imprecise height parameters), thereby providing
much more accurate estimates of your signal strength and phase variation at 830
km (for example).
I will search my database for 3kHz modal interference data at 3.5 km - 900 km;
thank you for a very interesting and significant experiment.
73,
Jim AA5BW
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of DK7FC
Sent: Monday, December 12, 2016 12:32 PM
To: [email protected]
Subject: Re: ULF: Finally 100 mA on 2.97 kHz
Hello Jim, ULF,
Am 12.12.2016 17:16, schrieb [email protected]:
> Congratulations on your ~20dB SNR at 65 km, 2970 Hz, that is quite a landmark
> supported by hard work.
>
Many thanks.
> You mentioned that the phase changes at 65 km do not seem to be from the
> transmitter, and that the phase changes are slow (I could not determine how
> slow from your earlier plot).
>
So far i don't know about the phase stability in 65 km distance. The observed
effect is from 3.5 km distance to the transmitter. In the attachment you can
see changing colours in the trace on 2970 Hz. You can also see timestamps and
the RDF circle, so you can get an impression about these changes.
> Does slow phase change (not from transmitter) lead you to suspect that the
> phase changes (and some signal strength variation) may be from modal
> interference (multiple rays interfering)? This question derives from modal
> interference being more prevalent and greater in magnitude at lower VLF and
> ULF frequencies, and distances less than 1,000 km. I didn't ask this before,
> because it would be unusual for modal interference to be a substantial issue
> at two widely separated locations (i.e at 65 km and at Todmorden). I didn't
> see mention of this possibility in Markus' comments so I'm wondering if this
> possibility is ruled out by other observations?
>
From summer recordings i saw that the sferics become very weak below and
arround 1.5 kHz, i daylight this cut off frequency is a bit higher, arround 2
kHz. You can see it quite clearly on this spectrogram from the
17 km experiment, which was in summer:
https://dl.dropboxusercontent.com/u/19882028/ULF/17kmwide.jpg
So at night the reflection height is higher, as far as i know arround 90 km.
Now 2.97 kHz is a factor 2 of this night cut off frequency. So the path from
the transmitter to the ionosphere and back is about 2 lambda at night and about
1.5 lambda in daylight?
Could this explain why the phase changes are stronger at night? 2 lambda would
be 2x 360 deg, which does not cause interferences and 1.5 lambda can cause a
compensation of groundwave and skywave?
I'm just trying to find an explanation from what i know so far.
Let us try to experiment with this phenomenon. Is it be possible to modulate
(pulse?) the carrier in a special way to see a result proofing the reflection
on the ionosphere, assuming the effect actually exists?
Markus will come up with an idea i bet :-) BTW i can run a two-tone signal
since i'm using a linear PA. However the freq deviation can only be a few Hz,
due to the low bandwidth of the antenna.
73, Stefan
> Your results today are great news, nice work!
>
> 73,
>
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