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Re: VLF: DK7FC close to SAQ

To: [email protected]
Subject: Re: VLF: DK7FC close to SAQ
From: DK7FC <[email protected]>
Date: Thu, 30 Nov 2017 13:50:54 +0100
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Hello VLF freinds,

I spent some day in Berlin, thus the late reply, sorry.
The carrier is actually running since 25.Nov 23 UTC witout any interruption! I have/had control over the TX via the samrtphone. I can follow the antenna current and can access the PC to stop the transmission if something would be wrong. Also there is the safety function that stops the transmission as soon as the antenna current drops by more than 30 mA under the target level of 700 mA.
Thanks to all stations who gave a feedback and RX report of the first
amateur transmission on 17.47 kHz.
Special congrats to IW4DXW who made his first amateur VLF reception at
all (i think)!
Riccardo, is that spectrogram really set to 3.8 mHz FFT bin width, as
stated in the text field?
Your simple antenna matching schmatic is apprechiated. It may be helpful
for further stations. I note that no special preamp is needed.
Luis, your few bright pixels look most promising. But maybe it is better
to wait until tomorrow before claiming that new distance record on the
17 km band. It would be a first amateur detection on VLF between DL and
EA! This evening i will finally rise the ERP by 3 dB, going from 700 mA
to 1 A antenna current... With 3 dB more, the few pixels should become a
solid line.
BTW all this helps to see how 'far' you are away from getting a
detection on 8270 and below..
Sq5BPF has set up a grabber but didn't see a trace so far. I started a
grabber window at RC4HAA running at 212 uHz. There is no trace at all! I
did expect much better results over that distance.
Also KL7L has set up a grabber window, without results so far.
My first impression is that the band offers less better propagation than expected! So let's hope that QRO will help :-)
Before loosing these informations i set up a small list containing
informations about RX stations and SNR reports, see attachment. Tell me
if there is something wrong or if i forgot something.
I will inform when the signal level has changed or when interruptions
happened. So far the transmission is still running. Ah yes the antenna
current ca be followed at
http://www.iup.uni-heidelberg.de/schaefer_vlf/VLF/TX.png Quite
unspectacular but some kind of feedback...
73, Stefan


Am 29.11.2017 22:46, schrieb Riccardo Zoli:
Hi Stefan, VLF

I got your signal in JN64bw, dear Stefan. Depending on the QSB and/or
QRN, you're peaking 15dB over noise. Fantastic! :-))
I'm using my LF antenna tuned on your QRG with a (approx.) 200mH coil.
The 17470.5 signal (locally generated by a GPS disciplined DDS) is
used for Spectrum Lab SR correction.
Schematic and capture attached.


Congrats, Stefan, and keep up the good work!

All the best,

73 de Riccardo IW4DXW



2017-11-26 0:40 GMT+01:00 DK7FC<[email protected]>:
Hi VLF,

Since 23 UTC a 700 mA carrier is running on 17.4701 kHz!

It is a little surprise to the VLF community i think ;-)

Legal? Yes:
http://www.iup.uni-heidelberg.de/schaefer_vlf/VLF/17,47kHz_Sonderlizenz.jpg
Actually the document has 3 pages but the other ones are no so relevant.
My ERP is limited to 5 mW. I did not request more because more isn't
possible anyway with this antenna.

I wound a big single layer coil with 0.5 mm enameled wire on a PVC tube with
315 mm outher diameter.

0.7 A is just a first careful step. The coil is designed to hold 1.5 A 'key
down'.

The carrier will run the whole night and even tomorrow at daytime.

Worldwide reports are welcome ;-)

It is not sub-9-kHz but still VLF, the 17 km band!! So give it chance :-)

The tree has still some solar power to stream the signal from the EW loop
down to the city, so there is a feedback spectrogram at
http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html


73, Stefan

PS: I still can hear that tone of the coil. It is terrible! Be happy when
you are older than me!

Attachment: 17470.png
Description: PNG image

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