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Re: LF: RE: EbNaut @ 80 Hz

To: [email protected]
Subject: Re: LF: RE: EbNaut @ 80 Hz
From: DK7FC <[email protected]>
Date: Thu, 29 Nov 2018 09:56:56 +0100
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Hello Jim,

Thanks for the kind words.

Well, the 60 Hz SNR is very weak here so the observations are limited. For me it looks like the 60 Hz trace is best visible in the morning, a few hours after my local sunset.

Both (all) spectrograms < 3 kHz are from the E field. The RDF spectrograms use the H field to define the colour only, see that explanation by DF6NM: http://df6nm.de/ColourDF/ColourDF.htm The mixing of the H fields is done in vlfrx-tools. This way the 3 channel stream becomes a 2 channel stream which is the fed to SpecLab.

My loops are not sensitive in that range. Something to improve soon.

Oh, did you actually see an unexpected SNR difference between the 3.8 mHz and the 424 uHz window?! This is very accurate observed. The reason is: The ZEVS window (3.8 mHz) uses a complex mixture of all 3 antennas, E, E-W,N-S to form a beam pointing towards ZEVS whereas the 424 uHz window simply shows the E field. But the H field components in the 3.8 mHz spectrogram are quite small, it is vtmix -c0.1/90,-0.25/-30,1/-20

The next step is to enter ELF of course. Yesterday i ordered some parts. The PA will be a special design, a HV cascade producing 40 kV DC. This DC voltage will be modulated with the ELF frequency. My plan is to try 23 Hz, the gap between the 3rd and 4th Schumann resonance, and later something lower than 10 Hz. So the DC voltage changes from 0 to 40 kV in a sine form. So the antenna will have a 20 kV DC component and a 40 kVpp AC component, i.e. abt 14 kV rms. This PA design works until including DC :-) It only works because the antenna current is sooo small and the ERP will be in the attowatt range.

73, Stefan



Am 28.11.2018 23:24, schrieb [email protected]:

Hello Stefan,

 

Your SLF (270 Hz, 80 Hz and 60 Hz) experiments and observations have been fascinating. It’s been enjoyable to guess what your next result would be; and encouraging to see that things at 270 Hz and 80 Hz seem fairly well behaved so far. It was also interesting to notice on your grabber that the 60Hz fading might not be diurnal.  

 

A question regarding your ZEVS and SLF spectrograms:

Does your ZEVS spectrogram (79.8 Hz – 83.2 Hz span) show lower SNR for your 80 Hz signal than your SLF spectrogram (79.95 Hz – 80.05 Hz span) because one comes from an H-field sensor in the forest and the other comes from an E-field sensor in the forest? The integration time difference (3.8mHz vs 424 uHz?) would seem to account for 9.5 dB lower SNR at 3.8 mHz, but the SNR in the ZEVS spectrogram (3.8 mHz) seems lower by more than 10 dB, so I wondered if the two spectrograms came from different antennas.

 

73,

 

Jim AA5BW  

 

From: [email protected] [mailto:[email protected]] On Behalf Of DK7FC
Sent: Tuesday, November 27, 2018 3:26 AM
To: [email protected]ksheep.org
Subject: SLF: EbNaut @ 80 Hz

 

Hi SLF,

Yesterday, a 45 character EbNaut was transmitted at 80.005 Hz. It was received on my tree in 3.5 km distance. After the improvement of the RX antenna it looks like i gained about 2.5 dB SNR. It was an easy decode, the message could have been transmitted 4 times faster.
Capture attached :-)

73, Stefan

PS: With that SNR, a 5 character message could be transferred out to 7 km distance in less than 1 day.



Am 23.11.2018 10:21, schrieb DK7FC:

Dear SLF friends,

A new step forward towards DC: Since yesterday 22:30 UTC i'm TXing a carrier at 80.005 Hz. That's the 3750 km band, where the far field begins at a distance of 598 km.

The antenna voltage is just 5 kV and i'm getting 1.2 mA antenna current, giving an ERP of  20 fW (2E-14 W).

The voltage is even higher than in my recent experiment on 270 Hz, anyway the S/N is lower, indicating that my RX lacks of sensitivity. Indeed this experiment helps to estimate the lack of sensitivity. Looks like i'm missing about 10 dB on that frequency. Anyway the signal is making the path of 3.5 km to my tree grabber, as usual shown at http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html. Not a big distance but still well beyond most garden fences!
The signal leaves a barely visible trace in the ZEVS window which is running at 3.8 mHz FFT bin witdh. Unfortunately ZEVS is off the air since a week or so. actually i wanted to transmit side by side with ZEVS, of course a bit deeper even.

>From a quiet period at night, i calculated the SNR of a 1 hour carrier period using vlfrx-tools: carrier S/N: 16.83 dB in 277.8 uHz, -18.73 dB in 1Hz

For the crazy homebrewers i'd like to share that website where i ordered the HV-transformer, http://www.hosin.de/Specials/HV-Trafo/hv-trafo.html A nightmare for all safety-fetishists! For the completeness it must be mentioned together with that page: http://kurts-werkstatt.de/hv-trafo.htm

73, Stefan

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