Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on lipkowski.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=5.0 tests=FREEMAIL_FORGED_FROMDOMAIN, FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS,HTML_MESSAGE,RCVD_IN_DNSWL_MED, SPF_PASS,T_DKIM_INVALID autolearn=ham autolearn_force=no version=3.4.0 X-Spam-DCC: : mailn 1480; Body=2 Fuz1=2 Fuz2=2 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by lipkowski.org (8.14.4/8.14.4/Debian-8+deb8u2) with ESMTP id v699ctMk003130 for ; Sun, 9 Jul 2017 11:38:57 +0200 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1dU8bl-000708-JW for rs_out_1@blacksheep.org; Sun, 09 Jul 2017 10:34:29 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1dU8bk-0006zz-ON for rsgb_lf_group@blacksheep.org; Sun, 09 Jul 2017 10:34:28 +0100 Received: from omr-m017e.mx.aol.com ([204.29.186.19]) by relay1.thorcom.net with esmtps (TLSv1:DHE-RSA-AES256-SHA:256) (Exim 4.89) (envelope-from ) id 1dU8bf-0008AZ-Vs for rsgb_lf_group@blacksheep.org; Sun, 09 Jul 2017 10:34:27 +0100 Received: from mtaomg-aac01.mx.aol.com (mtaomg-aac01.mx.aol.com [172.27.2.35]) by omr-m017e.mx.aol.com (Outbound Mail Relay) with ESMTP id 63229380008A for ; Sun, 9 Jul 2017 05:34:20 -0400 (EDT) Received: from core-acb01b.mail.aol.com (core-acb01.mail.aol.com [172.27.24.1]) by mtaomg-aac01.mx.aol.com (OMAG/Core Interface) with ESMTP id 10BAE38000081 for ; Sun, 9 Jul 2017 05:34:20 -0400 (EDT) Received: from 188.192.44.165 by webjas-vab174.srv.aolmail.net (10.96.18.177) with HTTP (WebMailUI); Sun, 09 Jul 2017 05:34:19 -0400 Date: Sun, 9 Jul 2017 05:34:19 -0400 From: Markus Vester To: rsgb_lf_group@blacksheep.org Message-Id: <15d26b31fb5-c01-17d82@webjas-vab174.srv.aolmail.net> In-Reply-To: <6c1f8a0c-0dd6-ed42-cfe6-4a142e7bd3cd@abelian.org> MIME-Version: 1.0 X-MB-Message-Source: WebUI X-MB-Message-Type: User X-Mailer: JAS STD X-Originating-IP: [188.192.44.165] x-aol-global-disposition: G DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mx.aol.com; s=20150623; t=1499592860; bh=eFwVma3Q8rJkLmkDfrZSlZimj912haBWzaLDFKZXh58=; h=From:To:Subject:Message-Id:Date:MIME-Version:Content-Type; b=J2dlEuwYn1QtRKNnXehGAd73JDbJ2YJhHf04gdDAOhHT6Kz9NqcXUJF/EvWcsR9R/ 6xhXL0f31VhSPKrTSg0t+RoFSirtK6YY/q0SFZUqMvy60bz404Ie2lwpe50534xhCE MMNDpCajMIjVPqONEf1uNQzREE8MArSsm771Vg1U= x-aol-sid: 3039ac1b02235961f89c0fb6 X-Scan-Signature: f82786fce13a7bdfc3036eb41b44b924 Subject: Re: LF: Octo-soundcard for the Raspi, another question Content-Type: multipart/alternative; boundary="----=_Part_123258_2058638565.1499592859572" X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-Scanned-By: MIMEDefang 2.75 Status: RO X-Status: X-Keywords: X-UID: 12202 ------=_Part_123258_2058638565.1499592859572 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Hi Stefan, Paul, this seems to be a weak effect: a sub-percent amplitude variation of a -50 = dB FS carrier would correspond to less than an LSB on an absolute 16-bit sc= ale. It's surely too small to compromise sensitivity of a real-world VLF re= ceiver.=20 First I thought it might be flicker noise on the ADC reference voltage but = why should it affect only three of six channels? Now I am wondering if it m= ight be an EMC issue, with undesired feedback from the digital data transfe= r to the analog inputs. With USB soundcards, the data packets are usually s= ent with 1 ms repeat rate, and we have sometimes seen an artifact consistin= g of weak 1 kHz spaced spectral lines. I do not know about the transfer pro= tocol of the Octo soundcard which is connected to the RasPi interface pins.= In case the packets are organized similarly, we might experience the same = problem, so 1 kHz or 0.5 kHz might have been just an unlucky choice for the= test signal frequency. Perhaps you could try again at some odd frequency? = Also a test at higher amplitude (e.g. -20 dB FS) would tell us whether it i= s a multiplicative (ADC scaling) or additive (EMC) error.. BTW This week I have received my Octo soundcard from the U.S. But I guess i= t will take some time until I have learned to install it on the RasPi and r= un vlf-tools under Linux. The warm summer is not a good time to bury onesel= f in the shack ;-) Best 73, Markus (DF6NM) -----Urspr=C3=BCngliche Mitteilung-----=20 Von: Paul Nicholson An: rsgb_lf_group Verschickt: Sa, 8. Jul 2017 19:40 Betreff: Re: LF: Octo-soundcard for the Raspi, another question Stefan wrote: > http://www.iup.uni-heidelberg.de/schaefer_vlf/VLF/record.tar Interesting. The first thing I notice is some curious effects on the background noise, on ch1 only, eg vtcat -S49 -E2 170708-095003 | vtrsgram -ox -g200 -- -:1 (ctrl-C in the shell to quit) or with vtsgram which uses sox as a back-end for the spectrogram vtcat -S49 -E2 170708-095003 | vtsgram -p200 | display There are lots of these: For a very wide image vtsgram 170708-095003 -p50 | display (Use the pan icon for panning and q to quit). Looking closely at the one at 24 seconds vtcat -S23.5 -E1 170708-095003 | vtrsgram -ox -g200 -- -:1 and vtcat -S23.5 -E1 170708-095003 | vtscope gives http://abelian.org/vlf/tmp/170708a.gif We can just see a slight change to the ch1 amplitude which lasts about 100mS. Can't really see anything obvious on the scope when zooming in on the start, http://abelian.org/vlf/tmp/170708b.gif The amplitude just seems to go up a tad at about 442 mS. Lets look at the phase during that same 1 second window vtcat -S23.5 -E1 170708-095003 | vtnspec -f1000 -w0 -r20 -k | awk '{printf( "%s %.1f\n", $1, atan2($4,$3)*180/3.14159)}' produces 1499507427.027 121.1 1499507427.077 120.9 1499507427.127 120.8 1499507427.177 120.6 1499507427.227 120.5 1499507427.277 120.3 1499507427.327 120.2 1499507427.377 120.0 1499507427.427 119.9 1499507427.477 119.7 1499507427.527 119.6 1499507427.577 119.4 1499507427.627 119.3 1499507427.677 119.1 1499507427.727 119.0 1499507427.777 118.8 1499507427.827 118.7 1499507427.877 118.5 1499507427.927 118.3 1499507427.977 118.2 Just shows a steady phase drift, we're not quite on frequency here with this recording - did it go through vttime? I see from vtstat -i 170708-095003 that we have sample rate: 24000, correction 0.99997722 The correction should always be 1.00000000 if the stream has been through vttime. Curious. Signal goes up, background noise drops. I wonder if there is a dodgy input capacitor or dry joint. Not sure about that explanation, it would be odd to see the same on more than one channel. Wonder if the effect occurs at the same time on ch1 and say ch4? Or instead the effect is independent on the effected channels. I will set my Octo up with the same test and look for the same effect here. -- Paul Nicholson -- ------=_Part_123258_2058638565.1499592859572 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable
Hi Stefan, Paul,

this seems to be a weak&nbs= p;effect: a sub-percent amplitude variation of a -50 dB FS carrier wou= ld correspond to less than an LSB on an absolute 16-bit scale. It's su= rely too small to compromise sensitivity of a real-world VLF receiver.=

First I thought it might be flicker noise on the ADC reference vol= tage but why should it affect only three of six channels? Now I am wonderin= g if it might be an EMC issue, with undesired feedback from the digita= l data transfer to the analog inputs. With USB soundcards, the data pa= ckets are usually sent with 1 ms repeat rate, and we have sometimes seen an= artifact consisting of weak 1 kHz spaced spectral lines. I do not kno= w about the transfer protocol of the Octo soundcard which is connected= to the RasPi interface pins. In case the packets are organized s= imilarly, we might experience the same problem, so 1 kH= z or 0.5 kHz might have been just an unlucky choice for the test signal fre= quency. Perhaps you could try again at some odd frequency? Also a test= at higher amplitude (e.g. -20 dB FS) would tell us whether it is a mu= ltiplicative (ADC scaling) or additive (EMC) error..

BTW This week I= have received my Octo soundcard from the U.S. But I guess it wil= l take some time until I have learned to install it on the RasPi = and run vlf-tools under Linux. The warm summer is not a good time= to bury oneself in the shack ;-)

Best 73,
Markus (DF6NM)

= -----Urspr=C3=BCngliche Mitteilung-----
Von: Paul Nicholson <vlf0403= @abelian.org>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org><= br>Verschickt: Sa, 8. Jul 2017 19:40
Betreff: Re: LF: Octo-soundcard for= the Raspi, another question


Stefan wrote:

> http://www.iup.uni-heidelberg.de/schaefer_vlf/VLF/record.tar<= /a>

Interesting. The first thing I notice is some curious effectson the background noise, on ch1 only, eg

vtcat -S49 -E2 170708-0= 95003 | vtrsgram -ox -g200 -- -:1

(ctrl-C in the shell to quit)
<= br>or with vtsgram which uses sox as a back-end for the
spectrogram
<= br> vtcat -S49 -E2 170708-095003 | vtsgram -p200 | display

There ar= e lots of these: For a very wide image

vtsgram 170708-095003 -p50= | display

(Use the pan icon for panning and q to quit).

Look= ing closely at the one at 24 seconds

vtcat -S23.5 -E1 170708-09500= 3 | vtrsgram -ox -g200 -- -:1

and

vtcat -S23.5 -E1 170708-0= 95003 | vtscope

gives http://abelian.org/vlf/tmp/170708a.gif

We= can just see a slight change to the ch1 amplitude
which lasts about 100= mS. Can't really see anything
obvious on the scope when zooming in on = the start,

http://abelian.org/vlf/tmp/170708b.gif

The amplitu= de just seems to go up a tad at about 442 mS.

Lets look at the phase= during that same 1 second window

vtcat -S23.5 -E1 170708-095003 |=
vtnspec -f1000 -w0 -r20 -k |
awk '{printf( "%s %.1f\n", $1, = atan2($4,$3)*180/3.14159)}'

produces

1499507427.027 121.1 1499507427.077 120.9
1499507427.127 120.8
1499507427.177 120.= 6
1499507427.227 120.5
1499507427.277 120.3
1499507427.327 1= 20.2
1499507427.377 120.0
1499507427.427 119.9
1499507427.47= 7 119.7
1499507427.527 119.6
1499507427.577 119.4
1499507427= .627 119.3
1499507427.677 119.1
1499507427.727 119.0
1499507= 427.777 118.8
1499507427.827 118.7
1499507427.877 118.5
1499= 507427.927 118.3
1499507427.977 118.2

Just shows a steady phase= drift, we're not quite on frequency here
with this recording - did it g= o through vttime? I see from

vtstat -i 170708-095003

that = we have

sample rate: 24000, correction 0.99997722

The corre= ction should always be 1.00000000 if the stream has been
through vttime.=

Curious. Signal goes up, background noise drops. I wonder if
th= ere is a dodgy input capacitor or dry joint. Not sure about
that explan= ation, it would be odd to see the same on more than
one channel.

= Wonder if the effect occurs at the same time on ch1 and say ch4?
Or inst= ead the effect is independent on the effected channels.

I will set m= y Octo up with the same test and look for the same
effect here.

-= -
Paul Nicholson
--

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