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Re: LF: testing VLF grabber

To: [email protected]
Subject: Re: LF: testing VLF grabber
From: DK7FC <[email protected]>
Date: Sat, 07 May 2016 00:35:41 +0200
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Hello Max,

Your motivation is pleasant. The stuff we all need to reach exciting results together :-)

Am 06.05.2016 23:30, schrieb Max IK0VVE:
Stefan, all,

I do not have time to reach you that you already run away to lower frequencies, HI.
Yes, sorry, it's a bit unpredictable what i'm doing these days but the are more transmit stations on 8.27 kHz. Also i will come back of course. And by this way i keep the center frequency 8.27 kHz free for other TX stations. I can try to decode EbNaut on 8.27 when transmitting on 6.47 during the same time.

I passed the last nights to try to discipline my audio board with my 1pps GPS... nothing to do, I've tried all, levels, phases, etc... I followed the Wolf's tutorial without success. I suppose duty cycle is to low. I'm waiting for a new GPS so I'll try with that or in the worst case with an OCXO+GPS 10khz.
Did you watch the signal on the oscilloscope and on the scope of SpecLab? I need more precise infos to give some advice, maybe a capture of the scope and the schematic how you coupled the module to the input.

So only for test now I'm pointing to German LF station DHO. Inserted BP and NB and moved to about 100uHz the resolution of the grabber.
Did you enable "1 pixel per FFT bin"? That would be recemmended.

Tomorrow a little trip, not so far, to an Ham friend to listen if his zone is quieter than where I live.

I'm interested to your Raspberry Pi remote system, can we get more informations?
Wow, of course that is a large project and i could write for hours. But a rough overview should be no problem:
-The Raspi 2B is used
-I'm using a 2.4 GHz link, with this yagi over a distance of 3.5 km in combination with USB WLAN Sticks (ALFA AWUS036NEH running in 'g' mode) connected to the Raspi.
-Two stereo USB soundcards are connected to the Raspi, one for MF, the other for VLF. The samplerate is 48 kS/s.
-The radio signals of MF are converted to a range of the soundcard (0...24 kHz), VLF comes in directly.
-Darkice and Icecast2 software is running as a web radio, vorbis stereo stream. Each stereo stream needs 20% CPU power, about.
-For VLF, i'm using the right channel to transfer 1 pps + NMEA signals from a cheap GPS module (13 €) which consumes just 40 mA at 3.3V. This allows to get an ultra stable signal which is necessary for the 47 uHz window.
-On the other end, SpecLab is playing the stream from it's IP adress, generates the first spectrogram ('wideband' on the top of the page ) and feeds the audio signal to VAC1. All other SL instances take the audio signal from VAC1 then, so the stream has just one client.
-There is a battery voltage and current monitoring so i can all the time monitor the energy situation on the tree. The curves are displayed at (I nned to cut some branches because the sun is now shining from a higher angle, so there is some shadow on the solar modules in the afternoon. But i don't want to cut them :-) In winter it is no problem...)
-There are additional circuits for protecting the batteries from deep discharges and there is a homemade accu charger that has a temperature regulated cutoff voltage.
-Currently 2 solar modules, 50Wp each, are used. And 3 lead gel accus 12V/18Ah.
- So far i prefer loop antennas for MF and VLF. Two orthogonal loops for each band, allowing RDF spectrograms. MF is running at , VLF is not so easy in RDF because the second channel is occupied by pps+NMEA. But there must be a solution!
- In previous versions of the system i used a bistabile relay to switch antennas remotely. That worked very well.
-The power consumption of the system is about 3W now since two soundcards + the GPS module + 40% CPU power is running permanently.

Don't know if you already started to play with the Raspi or if you are skilled in Linux. I spent dozens of hours to get it running as it is now. But there were great success moments many times. And i find the system availability is quite good, better then expected in the beginning.
I don't want to miss the project a single day :-)

73, GL, Stefan

Thanks, 73, Max IK0VVE

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