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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