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Re: LF: Octo-soundcard for the Raspi, another question

To: [email protected]
Subject: Re: LF: Octo-soundcard for the Raspi, another question
From: DK7FC <[email protected]>
Date: Thu, 06 Jul 2017 16:07:28 +0200
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Hi Paul,

I spent some more time on the 2 (3) channel portable VLF recorder using the Raspi, the octo-soundcard and vlfrx tools.
Meanwhile vttime is running. The GPS pulse is shortened to 2 ms (by
software). The shaping should be fine.
I managed to put all into a script so i can run/start/stop the receiver
without a mouse, keyboard and monitor. I can then disable the HDMI
output to save some more energy. The overall power consumption seems to
be 200 mA from a '12 V battery' (using a 85% efficient DC/DC converter
[a more efficient one is ordered]). That looks most promising!
I'm really looking forward to first 2 channel experiments and cardioidal
antenna mixing...
There are two problems that i am observing now:
I connected a sine function generator to both inputs (E and H antennas, later), at 500 Hz. Then i recorded a 2 channel 5 MB file using vtcard > vttime > vtresample > vtwrite on the Raspi. I moved that file to my Linux PC and converted it into a wav file using vtread | vtraw. When playing this file into SpecLab i can see the 2 channels and a strong carrier, as expected. However, channel 1 seems to show some minor glitches, see attachment. In SpecLab, the spectrogram is directly connected to L1,R1, no modification of the input signal.
Do you have an explanation for that effect?
When starting the recording (switching the record switch :-) ) i can see the processes when typing 'ps aux | grep vt'. As soon as the file is getting written i can see that the CPU load of vttime and vtresample increases continuously to very high values, see the vt attachment. vtps and vttop does not work. And strangely the process number of vtwrite is lower than vtresample, although vtresample has been started earlier.

I had to call the vlfrx tools from /usr/local/bin into that script, otherwise nothing happened. I call the script from the crontab when booting. Does this have to do with both problems?
What would you recommend?

73, Stefan

Attachment: 2ch.png
Description: PNG image

Attachment: vt.png
Description: PNG image

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