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RE: VLF: Carrier on 3675.005 Hz

To: <[email protected]>
Subject: RE: VLF: Carrier on 3675.005 Hz
From: <[email protected]>
Date: Sat, 5 Aug 2017 14:57:22 -0400
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Congratulations Stefan, Markus and DL0AO team!

 

Is this the first far-field link between 3.000 kHz and 4.000 kHz?

 

Another great data point in the previously uncharted and rough terrain of 2 kHz - 4 kHz, 100 km - 1000 km.

 

Analytical and computational estimates of path loss 2 kHz - 4 kHz, 100 km - 1000 km are at best somewhat (to considerably) speculative for lack of data, so I’d venture that the DK7FC/DF6NM/DL0AO team, and all those who provided receivers, transmitters and processing for prior tests 2 kHz - 6 kHz*, 100 km - 1000 km, have done valuable pioneering work.

 

(great work in hardware and processing, and especially pioneering work in characterization of propagation in a little-understood and not-too-friendly propagation realm 2 kHz - 4 kHz, 100 km - 1000 km)

 

From a spectator’s perspective this is very exciting.

 

 

   *  (5 kHz and 6 kHz tests helping to assess an upper boundary for the complicated 2 kHz - 4 kHz, 100 km - 1000 km space)

       (Much credit also to transmitter, receiver and processing work at 970 Hz making the interesting sub-kHz world accessible)  

 

 

Jim AA5BW

 

 

 

From: [email protected] [mailto:[email protected]] On Behalf Of Markus Vester
Sent: Saturday, August 5, 2017 8:35 AM
To: [email protected]
Subject: Re: VLF: Carrier on 3675.005 Hz

 

Yes the signal is definitely making it to Amberg! This is a fine result of mutual collaboration: Stefan DK7FC erecting the transmit facility and posing the low frequency challenge, the DL0AO team (specifically Tom DK1IS and Bernd DF9RB) laying out antennas in a quiet forest around their club station and installing dedicated hardware, and myself trying to tame 14 SpecLab instances without introducing too many errors.

The first indication of a 3675.005 Hz peak appeared already a couple of days ago on the E-probe antenna, and is still shown in the ultra-narrow 9.3 uHz window (waiting to be updated later tonight). Since yesterday, antenna and GPS connections have been greatly optimized, and the 31 uHz peak appeared early this morning after "only" 9 hours of averaging.

Best 73,
Markus (DF6NM)


-----Ursprüngliche Mitteilung-----
Von: DK7FC <[email protected]>
An: rsgb_lf_group <[email protected]>
Verschickt: Sa, 5. Aug 2017 11:17
Betreff: Re: VLF: Carrier on 3675.005 Hz

VLF,

After nearly 8 days the carrier is still on the air without an interruption, despite occasional thunderstorms :-)
It looks like the SNR is suffering by summer QRN, as expected.

The stable carrier was good for doing local tests with my Raspi+Octo-soundcard. The system is now completely configured including system time setting via the GPS module. I recorded a few days from the carrier, converted the data files into wav, reprocessed them in SpecLab: The carrier is stable and on the expected frequency, so the sample rate correction via vlfrx tools seems to work.

Forthermore i corrected some bugs in the circuit of my portable RX loop preamp for VLF (must have been late in the night when i built it up a few months ago). Now the noise is much lower. It looks promising! So it is time for a portable VLF experiment in the far field, just to check the system more seriously.

The crew of DL0AO has built up and optimised their VLF system to receive the weak 3675.005 Hz carrier in abt 220 km distance. Looks like there is something on their cardioidal spectrogram pointing to West,
http://df6nm.bplaced.net/dl0ao/VLFgrabber/vlfgrabber_dl0ao_test.htm
Something like 10 dB SNR in 31 uHz. That's not so bad!

I will run it for some more time until the trace is a bit longer. Then in some days i like to start transmitting an EbNaut message on that frequency which can be stacked until a decode appears. Markus has developed a tool for windows to do the stacking, maybe it works in that experiment... It will also be a test to see if i can decode the message from my own recording using vlfrx tools, an important step to pass...

So far so good. What are YOUR projects you are currently working on, LF/MF/VLF related?

73, Stefan


Am 28.07.2017 16:56, schrieb DK7FC:

Hi VLF,

I'm back from LF for a while and built up my large VLF coil which was used on 2970 Hz in the beginning of the year. Actually it is under maintenance, one of the six stacks has to be replaced. It is already dismantled but the new wire is not yet wound on the 250 mm diameter PVC tube again.
So now the resonance is higher! I didn't know where it is and just connected the coil and scanned the frequency downwards. Near 3685 Hz i found a maximum of the antenna. Since the Q is not extremely high, i decided to tune to 3675 Hz and added the usual 5 mHz offset, to stay away from multiples of 1 Hz.

So, now since 14:40 UTC a carrier is running on 3675.005 Hz. The antenna current is 170 mA. I estimate the ERP is just 3 uW!

I guess this is a first amateur radio transmission on the 82 km band and that class of ERP (?).

Hopefully the coil will hold the 15.5 kV with just 5 stacks of windings. It's inductance is 3.9 H in the moment!

I intend to run the carrier for at least a few days, depending on the feedback.

Good luck for the VLF experts!

73, Stefan

PS: A 424 uHz RDF spectrogram is running at http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html (First pixel appears in 30 minutes)

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