Well, well Stefan,
I was playing with the thought of "leaky" power line or cable
transmissions back in the days when 600 m opened up to a few select
countries (but not here in "Kekkoslovakia" despite the pressure from
me and some others). Since all kinds of "ethernet over mains" devices
etc. are legally free to spew out part of their output in the ether as
a "by-product" of their normal operation and so on it was kind of
logical reasoning. You get the point...
My message is: If you choose this path, why settle for just "legal
harmonics" when the whole RF spectrum may be yours to use? Just run it
into leaky cables and claim you are inventing a new mode of bringing
high-speed internet cheaply to every home. Even better, get some
generous EU-funding for it while you're at it :)
Could be easier to claim to be doing the above than getting a NOV
these days...
The above is purely meant as "food for thought", not as critisism
against the original idea.
Paul-Henrik, OH1LSQ
Quoting Stefan Schäfer <[email protected]>:
VLF,
That 3rd harmonic is on the 17 km band. Do we have any experiences
about local diurnal propagation?
Sooner or later there will be misunderstandings and some will say i
am transmitting on 17.265 kHz although the TX runs on 5.755 kHz!
I had a thought about that. 3rd harmonics are generated by all HF
amateurs, but we all ignore them. We actually can ignore them if
they are well attenuated but that doesn't mean that they do not
exist! BTW has someone ever tried to decode a 3HD signal (that name,
3HD, is just for fun, like the Dreamers band, a shortcut for 3rd
harmonic detection, reminds on HD quality movies or 3D glasses ;-) )
in OPERA mode?
_Example:_ When someone transmits a legal (!) QRO signal of 750W (in
DL) on the 160m band using a typical lambda/4 vertical (which is
radiating the 3HD signal because there it is lambda 3/4 and thus low
impedant too), using a 60 dB attenuating low pass filter, which is
quite a good supression, then there should be a 750uW signal on the
53m band, which could be detected in some distance, probably several
10km when using slow modes like OPERA-4 (WSPR will not work so
easily here). Receiving this 3HD signal is certainly not absolutely
strictly forbidden :-) So actually the amateurs can do legal QRPP
tests in slow modes on 53m, can't they? Would you think that it is
ethical unjustifiable to try to receive such a signal if it is there
anyway and legally generated?
_Example2_: PA0WMR is often TXing OP8 on 478.x kHz, making 2000km
distance. If someone in say 30 km distance can receive him on 1434
kHz (if there would be no AM BCD stn), close to the decode limit,
would something be wrong with this test?
I know from WSPR QRP transmissions from DL to VK on 15m with 0.1 W
TX power!! So i assume a 3HD signal could be detected in a few 100
km, maybe?
Below 8.3 kHz there is no TX power limitation and we can certainly
assume that no interference is caused to anyone at 3HD, just like in
the above example (53m band ( i never tried it)).So why not trying
to do tests like these today? The noise floor is much lower there
which improves the situation :-)
73, Stefan/DK7FC
Am 02.02.2014 18:15, schrieb Markus Vester:
Stefan,
your third harmonic is clearly visible in Holland
http://www.qsl.net/pa1sdb/
and here
http://www.df6nm.de/vlf/vlfgrabber.htm
Started spot-on 17265 Hz, now another peak is coming up 15 mHz up.
Good luck,
Markus (DF6NM)
*From:* Stefan Schäfer <mailto:[email protected]>
*Sent:* Sunday, February 02, 2014 3:27 PM
*To:* [email protected] <mailto:[email protected]>
*Subject:* Re: LF: DX VLF experiments in 3HD
Markus,
I am 16 dB stronger now!
Am 02.02.2014 14:52, schrieb Markus Vester:
So what should be expected here? Scaling the fieldstrength from 1
km to 180 km (1/r^3 to lambda/2/pi, 1/r thereafter), the signal
should be 82 dB weaker here on 5.755, and 63 dB weaker on 17.265
kHz. Neglecting ionospheric contributions (not really correct),
and assuming similar noise levels (though 5.5 kHz is much affected
by railway QRM here), my SNR in 0.47mHz should theoretically have
been
35 - 82 + 10 dB = -37 dB on 5 kHz and
50 - 63 + 10 dB = -3 dB on 17 kHz.
So while a detection on the fundamental seems pretty hopeless, the
third harmonic should already be getting close.
Yes, the QRN and QRM is much lower in 3HD :-) Why didn't we get
this idea earlier???
What is the inductance of the loading coil?
Ehm , i didn't really measured it, it's just trial and error.
Would be interesting to see a picture of the scope trace picked up
near the antenna ;-)
Looks quite good but could cause misunderstandings...
The amperemeter in the coil shows 350 mA now! There is some kind of
selfoscillations, audible. Thus i do not rise the power even more.
Have to search, find and fix this problem later. The AC voltage
from the vari-transformer is 110V now, so there is room for at
least another 6 dB. Power is in the range of 100W now.
I'm going to measure the strength at home now. Hopefully the signal
is audible :-) Yesterday it was still weaker than the mains hum, so
far away from any interferences!
73, Stefan
Best 73,
Markus (DF6NM)
*From:* Stefan Schäfer <mailto:[email protected]>
*Sent:* Sunday, February 02, 2014 2:06 PM
*To:* [email protected] <mailto:[email protected]>
*Subject:* Re: LF: DX VLF experiments in 3HD
Markus, VLF,
Am 01.02.2014 20:34, schrieb Markus Vester:
Stefan,
running two 478 µHz "6000" windows centered on 5755 Hz (on the
grabber, but much QRM here) and also 17265 Hz (offline) which
seems more quiet. So hoping for a long carrier...
Well, i hope that 16 hours key down were long enough ;-)
On which of the two frequencies would you expect to radiate more power?
I don't know. But the harmonic signal is very weak and cannot
cause interferences for JXN or HWU or SAQ or GBZ...
I've done measurements at home, 950m distance, of that _5.755 kHz_
transmission and saw that the signal was very weak, see
attachment. Just 50 dB SNR in 4.5 mHz at 3HD. The TX power was
just 15W at the end. Also the frequency response of the active
antenna + soundcard is attached.
The experiments are very interesting here and i like to do the
measurements. Despite rain the coil was on the top of the building
and on air. It was just covered by a trash bag. The voltages are
very small...
I just hang out a 30cm long wire connected to a probe of the
oscilloscope and so the voltage waveform of the antenna wire. It
nearly looks as expected :-)
Now i got another idea. There is a 2.2 uF WIMA MKP-10 capacitor in
series to the output of the H bridge, just to protect it against
damage in case of a DC output. Now i've disconnected the antenna
and tuned for the series resonance of this C and the L of the
primary winding of the loading coil. The resonance is at 1.77 kHz.
This allowed me to calculate a much smaller additional series C
which helps to attenuate unwanted frequency components, i.e. makes
the spectrum cleaner and provides a lower impedance on the wanted
frequency :-)
There is really no alternative to that H bride PA which works from
10 Hz to 100 kHz :-)
in a few minutes i will be on air again for a longer time,
hopefully with a much stronger signal.
Maybe you can detect something of that 5.755 kHz transmission.
73,GL, Stefan/DK7FC
BTW Today I have updated SpecLab from version 2.79 b08 to b10
(Jan 26), and it seems that GPS 1-pps sync is finally working
well now, even with 42 µHz resolution.
Good luck for the test!
73, Markus (DF6NM)
*From:* Stefan Schäfer <mailto:[email protected]>
*Sent:* Saturday, February 01, 2014 5:46 PM
*To:* [email protected] <mailto:[email protected]>
*Subject:* LF: DXl VLF experiments in 3HD
VLF,
This evening and night i'm planning to transmit on _*5.755 kHz*_,
using the large antenna, the large coil and the large PA :-)
I don't know what can be expected and how the system works at
that frequency. Actually it is just _a first test for playing
arround and doing some measurements_ :-)
If some nearby stations want to give it a try, maybe even in
*3HD*, then don't hesitate :-)
73, Stefan/DK7FC
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