Re: ULF: Finally 100 mA on 2.97 kHz / 65 km ULF experiment

[David Hine <evad_hine@yahoo.co.uk>]

This may seem VERY silly, but do you see your signals sometimes when not transmitting? If you do please let me know. Also does the received frequency / timings between transmissions get changed very slightly? Silly questions? -but not quite so silly at ULF -there are explanations if you notice these things Please let me know. Regards, David

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From: DK7FC <selberdenken@posteo.de>
To: rsgb_lf_group@blacksheep.org
Cc: Renato Romero <contact@vlf.it>
Sent: Friday, 9 December 2016, 14:43
Subject: Re: ULF: Finally 100 mA on 2.97 kHz / 65 km ULF experiment

After doing a lot of modifications here on the TX side, the effect still exists. I can't get rid of the unstable phase shown on the VLF tree grabber.

One thing to mention is that the phase seems to change slowly, no sudden phase jumps. Thus the peak is 40 dB S/N in 47 uHz. So obviously there were much less uncorrected phase glitches than expected in the first moment when i saw the effect.

Just to be sure i downgraded to the last SpecLab version, the one i used since the last month. But the effect still exists.

Next to note is the i never saw the effect in my last tests. I still have captures showing a very clear trace on 2970 Hz during the 31 km experiment. OK that was in September. The QRN levels may have been a bit higher and the signal was 7 dB weaker. So maybe the effect was just hidden in the noise?

Next i found that some SpecLab configurations seem to be corrupted by forth and back installing old (V2.90b2) and new (V2.92b2) version. So i am now using the old version and a config file that was never opened in the new version. It all seems to work fine on the TX side but i can still see the effect. BTW i even disabled the NB and checked if this makes a change. But thill the same result.

The TX schedule for the experiment is:
07.DEC: TX 2970.000 Hz (antenna current between 105...110 mA all the time) since 13:30 UTC. The recording has started about 15 UTC.

08.DEC: EbNaut 5ch, 80s, 8K19A @ 2970.000 Hz starting 7 UTC, ending 18:22:40 UTC. Then, carrier at 2970.000 Hz. Some interruptions happened in the late carrier.

09.DEC: 0 UTC starting DFCW-10800 (3h per element), 'dit' at 2969.9975 Hz, 'dah' at  2970.000 Hz. The message is 'FC'. Between F and C there is a break of 7 hours. In this time, starting 15 UTC: EbNaut 2ch, 68s, 8K19A @2970.000 Hz.

10.DEC: End of DFCW message 'FC' at 13 UTC. Then, EbNaut 5ch, 80s, 8K19A @ 2970.000 Hz starting 13 UTC (repetition of the message of 08.DEC.)

11.DEC: End of EbNaut message at 0:22:40 UTC. Then, carrier on 2970.000 Hz until 20 UTC. The recording will stopp in the late morning, due to space limitations of the 32 GB USB-stick.

>From the local recording i tried to decode the 5ch EbNaut message. But it didn't decode. I just got a '*****' message and a false decode. This is strange. The dots are quite concentrated in the two horizontal lines which indicates a stable phase. See attachment. Also the signal peak is strong and narrow. But in the red field there is nothing to see... This EbNaut message was transmitted with the new PSK config in SL. It is the reason why i will repeat the message in the end of the experiment again, using the old settings and version.

I should have done more pre-tests before starting the experiment. But now it is running. Well, the main goal is to detect a clear trace of my signal in a spectrogram running at 300 uHz or so. The signals do not look bad on the local grabber, not at all, despite the strange (propagation?) effect. I'm still optimistic...

73, Stefan


Am 08.12.2016 11:31, schrieb Markus Vester:

Hi Stefan,

>> I'm plotting the signal level and noise level, visible on the grabber.
At night, the signal becomes about 10 dB stronger while the noise
increases maybe 3 dB. The antenna current is super stable however. What
could the reason be? Propagation? I wouldn't assume that.
I do not see this effect on 6470 Hz.

This is really strange. There even seems to be something like a pre-sunrise dip before 6 UT. Maybe there is some resonance effect between the ionosphere and ground. But at this small TX-RX range, any reflection would need to be from a high angle, and it is hard to see how that could be excited by your electric transmit antenna.
 
Best 73,
Markus

-----Ursprüngliche Mitteilung-----
Von: DK7FC <selberdenken@posteo.de>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Do, 8 Dez 2016 12:42 am
Betreff: Re: ULF: Finally 100 mA on 2.97 kHz

Hi Paul,

Am 07.12.2016 14:50, schrieb Paul Nicholson:
>
> About 1uW should give some hint in a hour and very significant
> peak on an 8 hour spectrum.
I run a constant carrier from 13:30...7:00 UTC. On 7 UTC i will start an
EbNaut transmission for my local test: 5 chars 8K19A 80s. This takes
half a day about...
I also added a few plots and spectrograms to follow the transmission
from the tree
http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html
Also you can check the antenna current plot to get some more
information: http://www.iup.uni-heidelberg.de/schaefer_vlf/VLF/TX.png

BTW i put 5x 7 Ah accus there and am recording at 24 kS/s stereo to a 32
GB USB stick. The recording hast started about 15 UTC and i will drive
there (a trip of 2x 110 km!) again sunday morning to bring it back. Poor
accus, have to do that job below 0 C.
So i have more than 3 day time to run various transmission tests..

I'm plotting the signal level and noise level, visible on the grabber.
At night, the signal becomes about 10 dB stronger while the noise
increases maybe 3 dB. The antenna current is super stable however. What
could the reason be? Propagation? I wouldn't assume that.
I do not see this effect on 6470 Hz.

Update from 23:20 UTC: I found that the time server program has crashed!
:-( And it is an old PC so there are glitches from time to time.
Probably this is another reason why you don't see the faintest signal
:-( My grabber plots look quite good anyway, so maybe the problem hasn't
been so dramatic.
Now i'm watching the phase! And since 23:23 UTC it should be stable.
This may also explain the lower SNR in daylight, maybe it just has to do
with the number of phase jumps in one FFT :-(
A few things don't run as unproblematic as i would like but at least a
signal is on the air... I will sort out all problems by time...

>
> You made a long transmission with 30mA, from 2016-06-26_13:00
> to 2016-07-31_08:00, 34.79 days. No trace of the signal even
> with a coherent daily stacking gain of 15.4dB. Wait 58 says
> 0.036 fT for your ~100nW, which should have been visible in
> one day, say 8 hours.
>
> So something is not adding up. Maybe ERP is much lower
> than estimated, or the propagation near the mode 2 cut-off
> frequency is more attenuated or suffering a variable phase
> due to dispersion.
We will find that out! That's the interesting thing on this new land.
And i can rise the power by another 8 dB. But later...

73, Stefan