Hi Luis,
Am 31.07.2016 13:53, schrieb VIGILANT Luis Fernández:
Hi Stefan
Very nice experiment down there. Congratulations again :-)
Thanks. But so far there is no result. On monday i will drive there
again and hope to find the equipment and a few 10 GB of wav data :-)
But i'm optimistic. I took a short recording before i started the long
recording. It is for finding the equipment again because i didn't
exactly where i have been in the forest :-) The recording contains the
NMEA data and so the exact location :-)
On this recording i saw that the noise background is MUCH lower than on
the tree and in pre-tests in 5 km distance to the city.
Here is a spectrum of the recording with 250 ms scroll rate:
https://dl.dropboxusercontent.com/u/19882028/ULF/JN49KM.jpg
You see the resonance is a bit sharp and not perfectly on the frequency
but i hope it will work well anyway. It even looks like the gain of the
preamp is not sufficient. On the test QTH in 5 km distance to the city
the gain was high enough (the noise background increased 15 dB relative
to a dummy antenna). So this gives an idea how low the background noise
is in this location!
When this test is completed i will do another one in 30 km distance with
6 dB more pwoer :-)
I have been trying to track your calculations but got lost with your antenna
voltage figures
At 6470Hz with L=1.29H that should be an antena reactance of 52K Ohm, right ?
Right.
Then at 270mA antenna current that should be much more than 3.2KV ?
It will be 6.5 kV then.
Currently i am running 3.2 kV with this arrangement:
https://dl.dropboxusercontent.com/u/19882028/ULF/ULF%20loading%20coil%206.1H.jpg
Another question about your multi turn Rx loop. Any proteccion for nearby
lightings ?
Ehm, no :-) I will see if there is a problem later. I thought it is a
low impedant input, a NPN transistor, not a N-CH J-FET or OP AMP.
Ah BTW here is a photo of the loop in the forest:
https://dl.dropboxusercontent.com/u/19882028/ULF/20160730_170105.jpg
Not so easy to find between the trees but it is visible. The
circumference is 40m and the height above ground is maybe 4m.
And https://dl.dropboxusercontent.com/u/19882028/ULF/20160730_165911.jpg
shows the recording equipment which will hopefully not be stolen...
I'm planning to set a VLF Rx here and concerned about this. Would be a good
idea to
short the loop with a relay in case of nearby storm to protect the NPN and Rx
chain ?
I would rather tend to use anti-parallel diodes instead, maybe 2 or 3
pairs in series. Or maybe Z-Diodes. Must be checked if it has an effect
on the noise figure.
Where do you want to place it and what is the goal? Will you run a
grabber 24/7? Which of the bands is in the focus?
73, Stefan
73 de Luis
EA5DOM
________________________________________
De: [email protected] [[email protected]] en
nombre de DK7FC [[email protected]]
Enviado: domingo, 31 de julio de 2016 0:28
Para: [email protected]; Renato Romero
Asunto: Re: ULF: Key down signal on the 101 km band, still on the air
Hi all,
The 100 nW ERP 2970 Hz carrier has been on the air since 26th of June,
13 UTC. The transmitter phase has been stable since this time. There
were only a few very short interruptions, 90 minutes on the 17th of July
and then about 5 hours (5:45....11 UTC) on the 21st of July.
So it has been on the air since nearly 5 weeks.
The signal is still on the air but tomorrow 8 UTC i will do a frequency
shift of + 2.5 mHz. Later i will do an EbNaut test.
If someone still want to integrate the overall transmission into one
peak, tomorrow, 31th July 8 UTC will be the stop time.
In a few days i will then come back with a 6 dB stronger signal:
Coming from the LF world we assume that using a parallel capacitor to
the antenna is not a good idea. More C will mean less L, so you need
less wire and could think that this lowers the losses. But higher
currents are then needed which will cause even higher losses...
Thus i didn't consider to use a parallel C on ULF too. BUT on ULF, with
voltage limited systems it can be a good choice!
I run the yoghurt cup coil at 270 mA antenna current on my 470 pF
antenna at 6470 Hz. So it must have 1.29 H. So at 2970 Hz and 270 mA it
must have 6.5 kV! Currently i have about 3.2 kV. So with this
alternative matching i will get a 6 dB stronger signal.
I will then need 1.76 nF parallel to the antenna.
My 17 km distance experiment is running now! I have installed the loop
antenna somewhere in JN49KM. The Raspy is now recording stereo wav files
to the 32 GB USB stick... I'm using 2x 7 Ah lead acid gel batteries for
the supply. 1PPS+NMEA is used on the right channel.
73, Stefan
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