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Date: Sun, 31 Jul 2016 15:18:42 +0200
From: DK7FC <selberdenken@posteo.de>
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Subject: Re: ULF: Key down signal on the 101 km band, still on the air
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Status: O

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: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org] en nombre de DK7FC [selberdenken@posteo.de]
> Enviado: domingo, 31 de julio de 2016 0:28
> Para: rsgb_lf_group@blacksheep.org; 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
>