Hello Bill, VLF,
Thanks again for the interesting discussion!
In one point i have to disagree:
Am 16.07.2011 05:03, schrieb Bill de Carle:
I'm looking forward to a kite transmission in darkness - if you can
get out of bed that early, hi!
No problem! The exciting stuff makes me wake up easily, just as in the
10th experiment. :-)
I don't know much about SL
Disagreed! ;-)
so I just modified the vlf radio usr to get some data for the plot.
For the DHO38 SNR I used "avrg(23350,23450)-noise(23100,23700)" - far
from optimum,
This is quite interesting. I will arrange some SNR plots too. Sure, all
the possibilities of SL could be leaned from the help files but as other
OMs too do not like to read but rather experiment and learn from others :-)
You can confidently assume my receiving setup has room for
improvement! I've been making changes all along. I did not use noise
blanking for the wideband views
In the wideband views, sferics are an important and useful information,
so the spectrogram should be taken from L1, i.e. no noise reduction is
best. So you did it right of course.
but had some hard-limiting (software clipping) enabled for your last
8970 transmission.
OK, fine. Chris 4X1RF did a recording of my 9th experiment in December
2010. I've done several tests and found some settings that seem to be
very close to the optimum of noise reduction. There, a band limiting
filter is used, after that and combined clipping and blanking is
applied. Since the SL's noise blanker performance was improved, i found
no further improvements, so these settings are still close to the
optimum i think.
You could do some local tests and compare these settings to your own.
This can be done by setting up a small local TX on a small antenna or by
using the internal frequency generator or digimode terminal (connecting
to L1).
Of course i can send you a USR file for say "DFCW-2400" (1 mHz FFT bin
width) if wanted.
As to what next ... It's relatively easy to detect the presence of a
weak, stable carrier.
For SL, yes.
Do you know of any stable signal source (unmodulated carrier) near
8970 (somewhere near your QTH) I could look for?
No, the closest commercial transmitter near the Dreamers Band is the
lower Alpha TX at 11904.7619 Hz. It is worth to look out for that, just
to check if the system is running stable (i.e. locked to the reference
signal). You said you have a GPS reference frequency that can be down
divided below 24 kHz and then locked on, right?
I was thinking today of comparing a mini-whip Rx antenna to the
loops over 24 hours.
Excellent idea! It would have done that too but i have no suitable RX
loop so far. Tell us about the SNR difference. Maybe you can watch in
stereo mode (R= loop, L= probe) and show the traces in a splitted
spectrogram.
The property here is surrounded by tall trees and I can't think of
any easy way to get the probe above the treetops, away from
powerline. Perhaps a remote receiver, but that seems like a lot of
effort.
Maybe it works near the trees too. The signal level will be reduced,
anyway it might be OK as long as it is well above the soundcards noise.
On VLF this is easily done.
Looking at that chart you sent relating expected field strengths at
various distances and frequencies, I notice they specified a daytime
sea water propagation path. It would be nice to find some info about
spreading/distortion at 8970 Hz over the distance between here and
Germany.
Maybe someone can pass you a suitable link. But actually we have to make
our own experience which is not easy of course.
Looking forward to your tests.
73, Stefan/DK7FC
73,
Bill VE2IQ
At 09:25 PM 7/15/2011, you wrote:
Hello Bill and thanks for that very interesting picture! Actually we
should do the discussion on the reflector in order to keep some
common interest in the VLF stuff. We should try to leave the dreamers
dreaming! So if you want, we move to the official site! :-) Just put
your answer and the older stiff in CC to the reflector if its OK for
you....
Yes, Laurence and i think Jay also observed that dip just during my
sunset. Probably this is due to changing ionosphere height due to my
local sunrise, so the signal gets spread(?). Anyway the differences
are just a few dBs and not a few 10 dBs! So it is worth to try at any
time. But of course, it would be fine if these 3...6 additional dBs.
Someone out of my club has got a 5.5 kW generator that served the
whole fieldday stuff all the time without problems. He will probaly
be there in the next experiment. I expect to have at least 6 dB more
ERP the next time, i.e. 2 A antenna current or above. But it makes no
sense in August for us, probably...
Thanks for your work and i'm watching your grabber regularly in the
last weeks. I shall ask the air traffic control for a special special
permission for research purposes to fly that kite in the darkness!
BTW how have you done the SNR calculations in SL? This would be
interesting for me.
Another question is how representative DHO38 is for anylysing the
Dreamers Band propagation. Actually we have to get our own experience
on that band to get a better idea. Long time transmissions of a
stable (constant ERP) signal would be necessary. I shall repeat my
VLF TX tests on the fixed antenna in some months.
What do you think we could try to prepare else? Your loop is
correctly arranged? Your frequency is locked to GPS? Your PC is
stable running, making recordings and captures? Are you using the
optimised USR files for blanking the noise?
If i would TX this weekend, what SL settings would you use? Could you
send me that USR file? Maybe we can discuss the settings before, even
if nothing is lost as long as you do a recording. This recording
should include the reference frequency, like an injected 10 kHz ref
like you can see on my wideband grabber. This doesn't need to be on
the second channel, thinking about the file size for the recording.
My Dropbox space is 4 GB no, so we can exchange big files ;-)
73, Stefan/DK7FC
PS: It would be fine to have an overview of the entire VLF band like
OK2BVG supports. This gives an excellent overview to your location
and its local QRN/QRM. Especially the sferics are interesting!
Am 15.07.2011 14:07, schrieb Bill de Carle:
At 12:54 PM 7/7/2011, you wrote:
Ah, now the picture builds up! Looks fine. The curve is about 10 dB
above the soundcard noise on 9 kHz which is a bit low. 20 dB would
be better i think. Anyway very good view!
Maybe you can run the window slowly to show several hours. Then we
will se when and if and how you can receive DHO38 and the Alphas
and JXN and so.
A slow running "DFCW-6000" window would be excellent too :-)
73, Stefan
PS: See that noise on my grabber!!! ;-)
Stefan:
Here's a look at the DHO38 SNR's over 2 consecutive early morning
enhancements:
http://www.nrtco.net/~ve2iq/grabs/grab3.gif
Bill
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