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Stefan,
unfortunately nothing was detected here, neither on
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.
What is the inductance of the loading coil?
Would be interesting to see a picture of the scope trace picked up near the
antenna ;-)
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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