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Stefan,
your third harmonic is clearly visible in
Holland
and here
Started spot-on 17265 Hz, now another peak is
coming up 15 mHz up.
Good luck,
Markus (DF6NM)
Sent: Sunday, February 02, 2014 3:27 PM
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)
Sent: Sunday, February 02, 2014 2:06 PM
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)
Sent: Saturday, February 01, 2014 5:46 PM
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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