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x-ms-office365-filtering-correlation-id: aeb89446-c863-4ade-2562-08d4823e87fd x-microsoft-antispam: UriScan:;BCL:0;PCL:0;RULEID:(22001)(201702061074)(5061506573)(5061507331)(1603103135)(2017031320274)(2017031324274)(2017031323274)(2017031322274)(1603101448)(1601125374)(1701031045);SRVR:VE1EUR02HT193; x-exchange-antispam-report-cfa-test: BCL:0;PCL:0;RULEID:(444000031);SRVR:VE1EUR02HT193;BCL:0;PCL:0;RULEID:;SRVR:VE1EUR02HT193; x-forefront-prvs: 02760F0D1C spamdiagnosticoutput: 1:99 spamdiagnosticmetadata: NSPM MIME-Version: 1.0 X-OriginatorOrg: hotmail.com X-MS-Exchange-CrossTenant-originalarrivaltime: 13 Apr 2017 07:27:24.5930 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Internet X-MS-Exchange-CrossTenant-id: 84df9e7f-e9f6-40af-b435-aaaaaaaaaaaa X-MS-Exchange-Transport-CrossTenantHeadersStamped: VE1EUR02HT193 X-Scan-Signature: 8ac9f0a1bced50a7ada6578ede3fb6ae Subject: Re: VLF: DFCW-6000 Content-Type: multipart/alternative; boundary="_000_LO1P123MB1364B59B5415195A81FE644BD1020LO1P123MB1364GBRP_" 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: O X-Status: X-Keywords: X-UID: 11246 --_000_LO1P123MB1364B59B5415195A81FE644BD1020LO1P123MB1364GBRP_ Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Blue sky idea: Might it be possible to subtract (rather than filter) the hum from the sign= al, being as it is such a constant source ? Either with analogue electronics, or via digital signal processing: Might = it be possible to detect the phase of the hum on the original signal, then = build a model from sine waves of what the summed odd harmonics might look l= ike for the first few octaves, and then subtract that from the original sig= nal to get one with reduced hum ? Best Regards, John. G7JMZ ________________________________ From: owner-rsgb_lf_group@blacksheep.org on behalf of Paul Nicholson Sent: 10 April 2017 20:49 To: rsgb_lf_group@blacksheep.org Subject: Re: VLF: DFCW-6000 > Meanwhile the 7 is completed :-) In the time it took to send 'DK7' you could have sent 330 characters using a more efficient mode. Or sent DK7 with a signal 20dB weaker. From a nearby thread: > if you could release a new ebnaut-tx.exe for Windows > which handles 200 characters and 0 CRC bits, i would > send you a 200 character long message. That's in the next revision, and some other alterations which I hope I can finish testing soon. This talk of longer messages makes me wonder about the possibility of arranging a source encoding for binary data. How about sending a .jpg at VLF? Crazy, but just about feasible. Eddie wrote: > Loops at this QTH are not very successful, yes lots of > mains borne QRM. Often, H-field is worse. You have not only the harmonics, but the sidebands of the harmonics to deal with. My rural location is very noisy from the mains. All the farms around here are supplied by overhead lines. My loops are about 200m from the house which is plenty far enough not to pick up any domestic interference. I think 100m would have been good enough. Moving away from the nearest power line the hum falls off with distance cubed as you would expect, but by 100m falls to a background level unrelated to nearby lines and further distance is no better. I presume this hum floor comes from more distant national grid lines. The H-field hum level varies a lot but is unrelated to local loads. I wouldn't worry too much about the mains hum level. It's a fact of life and is not going to go away. But if it is fairly clean hum (not too many sidebands) and your rx and A/D are impeccably linear, then there's plenty of space between the hum harmonics for reception down to the natural noise floor. I should perhaps post a short mp3 of my raw unfiltered H-field ... http://abelian.org/vlf/tmp/170410a.mp3 You wouldn't think it possible to pick up anything through that. If I filter out the hum harmonics, you can hear the sidebands. The filter kicks in at about 5 seconds: http://abelian.org/vlf/tmp/170410b.mp3 Here's the same thing from the E-field rx http://abelian.org/vlf/tmp/170410c.mp3 Note the much lower level of sidebands on the E-field. In the UK it is hard to find anywhere clear of foreground hum. But with a bit of effort you can often reach the natural noise floor in a suburban location. -- Paul Nicholson -- --_000_LO1P123MB1364B59B5415195A81FE644BD1020LO1P123MB1364GBRP_ Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

Blue sky idea:


Might it be possible to subtract (rather than filter) the hum from the s= ignal, being as it is such a constant source ?


Either with analogue electronics, or via digital signal processing: = ; Might it be possible to detect the phase of the hum on the original = signal, then build a model from sine waves of what the summed odd harmonics= might look like for the first few octaves, and then subtract that from the original signal to get one with reduced hu= m ?


Best Regards,

John. G7JMZ

From: owner-rsgb_lf_group= @blacksheep.org <owner-rsgb_lf_group@blacksheep.org> on behalf of Pau= l Nicholson <vlf0403@abelian.org>
Sent: 10 April 2017 20:49
To: rsgb_lf_group@blacksheep.org
Subject: Re: VLF: DFCW-6000
 

 > Meanwhile the 7 is completed :-)

In the time it took to send 'DK7' you could
have sent 330 characters using a more efficient
mode.

Or sent DK7 with a signal 20dB weaker.

 From a nearby thread:

 > if you could release a new ebnaut-tx.exe for Windows
 > which handles 200 characters and 0 CRC bits, i would
 > send you a 200 character long message.

That's in the next revision, and some other alterations
which I hope I can finish testing soon.

This talk of longer messages makes me wonder about the
possibility of arranging a source encoding for binary
data.   How about sending a .jpg at VLF?   Crazy, but j= ust
about feasible.

Eddie wrote:

 > Loops at this QTH are not very successful, yes lots of
 > mains borne QRM.

Often, H-field is worse.  You have not only the harmonics,
but the sidebands of the harmonics to deal with.

My rural location is very noisy from the mains.  All the
farms around here are supplied by overhead lines.  My loops
are about 200m from the house which is plenty far enough
not to pick up any domestic interference.    I think 100m would have been good enough.

Moving away from the nearest power line the hum falls off
with distance cubed as you would expect, but by 100m falls
to a background level unrelated to nearby lines and further
distance is no better.  I presume this hum floor comes from
more distant national grid lines.   The H-field hum level
varies a lot but is unrelated to local loads.

I wouldn't worry too much about the mains hum level.  It's
a fact of life and is not going to go away.  But if it is
fairly clean hum (not too many sidebands) and your rx and
A/D are impeccably linear, then there's plenty of space
between the hum harmonics for reception down to the
natural noise floor.

I should perhaps post a short mp3 of my raw unfiltered H-field
...

  http://abelian.org/vlf/tmp/170410a.mp3

You wouldn't think it possible to pick up anything through that.

If I filter out the hum harmonics, you can hear the sidebands.
The filter kicks in at about 5 seconds:

  http://abelian.org/vlf/tmp/170410b.mp3

Here's the same thing from the E-field rx

  http://abelian.org/vlf/tmp/170410c.mp3

Note the much lower level of sidebands on the E-field.

In the UK it is hard to find anywhere clear of foreground hum.
But with a bit of effort you can often reach the natural noise
floor in a suburban location.

--
Paul Nicholson
--

--_000_LO1P123MB1364B59B5415195A81FE644BD1020LO1P123MB1364GBRP_--