Hi Luis,
Am 02.05.2017 10:49, schrieb VIGILANT Luis Fernández:
I was already running an SL
instance showing the first 24KHz in a fast way to get an idea of what's
going on with QRM and known signals
It is already included in the
grabber at 1 min/pixel. Hour changed to UTC just now
Yes but it starts at 6 kHz, so not the first 24 kHz ;-) From 0...6 kHz
there are also informations which are relevant to evaluate the
situation of your receiver(site).
As you can see, there is a LOT
of noise around. What I'm using is your VLF E-Field probe with the
first JFet separated in a 50cm aluminium rod probe
Not only the length of the rod, also the height above ground, the
effective height, playes an even bigger role. Sourrounded by trees you
miss sensitivity, the lower the frequency is. And on the top of a high
tower, the signals will be much stronger, with the same rod!
If there is a strong local AM transmitter on MF, you may get some
interferences, and so on. Thus it is good to see what happens below 6
kHz too.
When DLF on 153 kHz has been active here, running 500 kW to a 350m high
antenna in 40 km distance, i sometimes saw AM components, demodulation
stuff on VLF, in one of the first versions. So when the antenna is on a
high tower and the signal levels are strong, you may afford a second RC
low pass filter in front of the first JFET, giving a cleaner spectrum
on the lower VLF. On the other side, with a longer rod (giving more
capacity) you may decrease the 10 MOhm resistor. This should reduce the
noise of the first JFET a bit.
I just played with all that stuff a week ago when optimising my ULF E
field circuit for 970 Hz.
Obviously, no clear trace from your last
transmission in the 31mHz spectrogram with this Rx conditions
31 mHz? That's quite optimistic! I would rather try 31 uHz.
Are you using an AF isolation transformer between soundcard and
antenna? What type of power supply are you using for the antenna? Is
the GND of the antenna separated from the mains earth?
So, 7Km is an outstanding Dx at
this moment. But really challenging
I do already have a failed microwave oven to use
the transformer. And the audio PA too. So you mean to apply the high
voltage to the antenna
without
resonating coil, right ?
Yes.
Better start with some measurements in the shack, not on the roof :-)
Measure or estimate the capacity of your antenna. Switch a fixed C of
that value parallel to the transformer. Use a sine signal generator
connected to the audio PA. Try to find a resonance or check the voltage
at 8270 Hz. Maybe a normal mains transformer 12V -> 230V will give
better results! Maybe you need to add your own primary winding to the
transformer. Try to get 1 kV or so, that should work well. With a mains
transformer, 500V may work for a few hours. If you have a toroidal
transformer, use that!
You can also switch an external C parallel to the transformer if that
helps to rise the voltage on the desired frequency. Or switch it in
series to the primary winding. Ah and a resistor, maybe 2 Ohm or so may
help to protect the PA from transients and short cuts (resonances).
Nice therm. Don't know if the pipe running
down to ground would have any issue with this. At the moment 80w at MF
didn't show to be harmful
But there can be some noise at 8KHz and
this would really be an annoying side effect if that happens :(
The antenna currents will be very low. There will be no unwanted
effects, except maybe some local E field coupling on the roof.
The resonating coil for VLF is in the "To-Do"
list. Actually found a huge plastic (resin) garden flowerpots which are
60cm diameter by 35cm high
This can be stacked upside down leaving airgap
between them for ventilation. Just adding one final on top with no coil
serves as rain protection
of the full arrange.
Maybe it's a good idea to start in small steps. With your own monitor
you will have some first results. And maybe some of the local EA
amateurs can help to reach the next distance step :-)
It is all not easy! I would say it is harder than EME ;-)
73, Stefan
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