Return-Path: X-Spam-DCC: paranoid 1233; Body=2 Fuz1=2 Fuz2=2 X-Spam-Checker-Version: SpamAssassin 3.1.3 (2006-06-01) on lipkowski.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=5.0 tests=BAYES_00,DNS_FROM_AHBL_RHSBL, HTML_10_20,HTML_MESSAGE autolearn=no version=3.1.3 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by paranoid.lipkowski.org (8.13.7/8.13.7) with ESMTP id t8QElXP7031529 for ; Sat, 26 Sep 2015 16:47:33 +0200 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1ZfqgE-0007bE-Ml for rs_out_1@blacksheep.org; Sat, 26 Sep 2015 15:42:26 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1ZfqgE-0007b5-9e for rsgb_lf_group@blacksheep.org; Sat, 26 Sep 2015 15:42:26 +0100 Received: from mail-wi0-f169.google.com ([209.85.212.169]) by relay1.thorcom.net with esmtps (TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128) (Exim 4.86) (envelope-from ) id 1ZfqfA-00042S-6w for rsgb_lf_group@blacksheep.org; Sat, 26 Sep 2015 15:42:25 +0100 Received: by wiclk2 with SMTP id lk2so54267881wic.0 for ; Sat, 26 Sep 2015 07:41:04 -0700 (PDT) X-DKIM-Result: Domain=gmail.com Result=Good and Known Domain DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; bh=/TJnR0UU6lHXLaOFLdHF/MVpA8QnoAAm4DxbpApMGG4=; b=DXy1BSm2R1dPf3BCNnLCjRrnnt7g9luxyBQK0JJIEPNym7lvlXN8S24nQhodeUTn/t SNvXyvtL0p55uYPivOqaemeNV8Z3D7KNAYm+p3cUISOeilpg/2TsLpn2pBCyTPQhbAGF bH3+e90IL4XXn0OvAU/U2F0YjYVhcLT/n+PixFj7rCjxx5x/NAQkaW8MM3Yzgy6dmp5c qAySDNzRqyea3Zh3szoRdCZtmHyxfzjYp+o2GokJL4tw1AwgI601ROTZjAMJK6R43YGT hKdm1iu/l26DIZwJMPBg0gWxzQQ4lpmFbdfFV4gh1jz9ulqdcoM4PlLM4AIVnoJKtdmQ qCrQ== MIME-Version: 1.0 X-Received: by 10.180.188.169 with SMTP id gb9mr9721497wic.72.1443278463875; Sat, 26 Sep 2015 07:41:03 -0700 (PDT) Received: by 10.28.47.212 with HTTP; Sat, 26 Sep 2015 07:41:03 -0700 (PDT) In-Reply-To: <56069AD1.4040303@abelian.org> References: <5601EC9F.2010607@gmail.com> <56059B48.80606@freenet.de> <56069AD1.4040303@abelian.org> Date: Sat, 26 Sep 2015 15:41:03 +0100 Message-ID: From: Andy Talbot To: rsgb_lf_group@blacksheep.org X-Scan-Signature: 350b42a0642244046701ed1a68bf48aa Subject: Re: LF: Coherent BPSK on LF using EbNaut Content-Type: multipart/alternative; boundary=001a11c26bb826c25e0520a774f2 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 2.56 on 10.1.3.10 Status: O X-Status: X-Keywords: X-UID: 4158 --001a11c26bb826c25e0520a774f2 Content-Type: text/plain; charset=UTF-8 Yessss... Hadn't appreciated that was what it was doing until I read the description in more detail. I suppose that if soundcards are going to be used as the interface some sort of locking will have to be used. G3PLX used his clicklock technique for phase coherency, where the 1 PPS is bled into the receive path. You go one further and mix in the NMEA stream audio as well for time stamping. A neat solution to making use of what is really unsuitable hardware. Soundcards really aren't precision measurement tools ! It may be time to revisit the LF receiver in that case. Something like a direct I/Q downconversion from LF to baseband, low pass filtering then I/Q sampling into an A/D at something like 1kHz (or even lower), sending the resulting samples to a PC using a basic USB (or even a COM ) port. Then for backwards compatibility adding in the GPS timestamp information in the same way . Getting a certain sense of Deja-vue here. Back when LF was new, and soundcards were rarely used for radio and GPS receivers rare, I did start to build a custom LF Rx doing just this technique and managed to receive coherent carriers from such as MSF and the Swiss one and see how their phase shifted with the ionosphere. For freqeuncy reference I used my caesium standard. But it never went anywhere long term on 73 & 137kHz because a) PC technology moved faster and everyone else was adopting soundcard ideas and b) The PIC processors I was using were still new than and had pretty basic functionality making everything hard work and c) no one seemed bothered since QRSS has just become widely popular and they all used that mode. N ow, nearly 20 years later, the direct conversion LF receiver (Softrock type perhaps) and a new generation of processor chips make the job a lot easier. DDS or Fract-N synth LO, Quadrature mixer, simple (just analogue perhaps) low pass filter, dual A/D , PIC, PC interface Andy G4JNT On 26 September 2015 at 14:17, Paul Nicholson wrote: > > Very nice to see this working at LF with short symbols. > The phase was stable enough for the 20 or so minutes of each > transmission on this path of circa 1000km. > > S/N of IZ7SLZ at DF6NM suggests that a contact would not have > been possible (at this symbol rate and signal strength) without > using coherent detection - it would be a few dB too weak. > > The phase looks pretty steady. The ionosphere and the local > oscillators are both looking very good here. I wonder how > long the phase can keep stable for - or in other words, the > max message duration? > > A fine achievement, well done to both. It's great to see a > two-way contact using this mode and this demonstration that > it works at LF opens up some interesting possibilities. > > Andy Talbot wrote: > > > Unfortunately, I see it is not standalone, and requires > > Spectrum lab to act as the audio "front end" ... > > Spectrum Lab in fact does most of the work: Digitising > the audio, frequency shifting and the delicate business of > resampling with reference to GPS pulses so that each audio > sample is UT synchronous and at a constant sample rate. > Then there is filtering and if necessary, noise (sferic) > blanking. SL even handles the decoding of GPS messages so > that it can accurately time the reception. After all that, > ebnaut is just a small 'back-end' decoder. > > This mode is not easy to use. It requires some technical > skill to arrange atomic quality reference oscillators at > each end and to get the software set up correctly. > > For those that can rise to the challenge, the potential gain > is several dB over any other mode on paths where the phase > is fairly stable for the duration of a transmission. > > Coherent BPSK has been used for amateur satellites and packet > networks, for a long time. These applications extract a > reference phase from the received signal (using a Costas loop > or equivalent). EbNaut works even when the signal is too weak > to extract a reference phase. > > More info at > > http://abelian.org/ebnaut/ > > -- > Paul Nicholson > -- > > --001a11c26bb826c25e0520a774f2 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Yessss...
Hadn't appreciated that was what it was = doing until I read the description in more detail. =C2=A0 I suppose that if= soundcards are going to be used as the interface some sort of locking will= have to be used. =C2=A0 G3PLX used his clicklock technique for phase coher= ency, where the 1 PPS is bled into the receive path. You go one further and= mix in the =C2=A0NMEA stream audio as well for time stamping. =C2=A0 A nea= t solution to making use of what is really unsuitable hardware.=C2=A0 Sound= cards really aren't precision measurement tools !

<= div>It may be time to revisit the LF receiver in that case. =C2=A0 =C2=A0So= mething like a direct I/Q downconversion from LF to baseband, low pass filt= ering =C2=A0then I/Q sampling into an A/D at something like 1kHz (or even l= ower), sending the resulting samples to a PC using a basic USB (or even a C= OM ) port.=C2=A0 Then for backwards compatibility adding in the GPS timesta= mp information in the same way .

Getting a certain= sense of Deja-vue here. =C2=A0 =C2=A0Back when LF was new, and soundcards = were rarely used for radio and GPS receivers rare, I did start to build a c= ustom LF Rx doing just this technique and managed to receive coherent carri= ers from such as MSF and the Swiss one and see how their phase shifted with= the ionosphere. For freqeuncy reference I used my caesium standard. =C2=A0= =C2=A0But it never went anywhere long term on 73 & 137kHz because a) P= C technology moved faster and everyone else was adopting soundcard ideas an= d b) =C2=A0The PIC processors I was using =C2=A0were still new than and had= pretty basic functionality making everything hard work =C2=A0and c) no one= seemed bothered since QRSS has just become widely popular and they all use= d that mode.
N
ow, nearly 20 years later, the direct co= nversion LF receiver (Softrock type perhaps) and a new generation of proces= sor chips make the job a lot easier. =C2=A0=C2=A0
DDS or Fract-N = synth LO, Quadrature mixer, simple (just analogue perhaps) low pass filter,= dual A/D , PIC, PC interface


Andy = =C2=A0G4JNT=C2=A0


<= br>
On 26 September 2015 at 14:17, Paul Nicholson= <vlf0403@abelian.org> wrote:

Very nice to see this working at LF with short symbols.
The phase was stable enough for the 20 or so minutes of each
transmission on this path of circa 1000km.

S/N of IZ7SLZ at DF6NM suggests that a contact would not have
been possible (at this symbol rate and signal strength) without
using coherent detection - it would be a few dB too weak.

The phase looks pretty steady.=C2=A0 The ionosphere and the local
oscillators are both looking very good here.=C2=A0 I wonder how
long the phase can keep stable for - or in other words, the
max message duration?

A fine achievement, well done to both.=C2=A0 It's great to see a
two-way contact using this mode and this demonstration that
it works at LF opens up some interesting possibilities.

Andy Talbot wrote:

> Unfortunately, I see it is not standalone, and requires
> Spectrum lab to act as the audio "front end" ...

Spectrum Lab in fact does most of the work:=C2=A0 Digitising
the audio, frequency shifting and the delicate business of
resampling with reference to GPS pulses so that each audio
sample is UT synchronous and at a constant sample rate.
Then there is filtering and if necessary, noise (sferic)
blanking.=C2=A0 SL even handles the decoding of GPS messages so
that it can accurately time the reception.=C2=A0 After all that,
ebnaut is just a small 'back-end' decoder.

This mode is not easy to use.=C2=A0 It requires some technical
skill to arrange atomic quality reference oscillators at
each end and to get the software set up correctly.

For those that can rise to the challenge, the potential gain
is several dB over any other mode on paths where the phase
is fairly stable for the duration of a transmission.

Coherent BPSK has been used for amateur satellites and packet
networks, for a long time.=C2=A0 These applications extract a
reference phase from the received signal (using a Costas loop
or equivalent).=C2=A0 EbNaut works even when the signal is too weak
to extract a reference phase.

More info at

=C2=A0http://abelian.org/ebnaut/

--
Paul Nicholson
--


--001a11c26bb826c25e0520a774f2--