Return-Path: X-Spam-DCC: paranoid 1170; 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=-2.4 required=5.0 tests=BAYES_00,DNS_FROM_AHBL_RHSBL, 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 tA1J5F6I014801 for ; Sun, 1 Nov 2015 20:05:15 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1Zsxsf-0004KT-9p for rs_out_1@blacksheep.org; Sun, 01 Nov 2015 19:01:29 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1Zsxse-0004KK-M3 for rsgb_lf_group@blacksheep.org; Sun, 01 Nov 2015 19:01:28 +0000 Received: from mail-wm0-f46.google.com ([74.125.82.46]) by relay1.thorcom.net with esmtps (TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128) (Exim 4.86) (envelope-from ) id 1Zsxra-0006jt-BF for rsgb_lf_group@blacksheep.org; Sun, 01 Nov 2015 19:01:27 +0000 Received: by wmff134 with SMTP id f134so43652390wmf.1 for ; Sun, 01 Nov 2015 11:00:06 -0800 (PST) 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=xvJL5662k6hVRTAR2/QAkPGbNtMi4YgThSzdamsKRXo=; b=xhXEIBpm69UYQAGH++S0P5WP4jemek3py/dk8hLIQZFOhocSgZNxx1wkxLkyWRn0xP uXiyf6xcc8GZ7M4MDnKgiUjhsPBkpOKeQQb3uSoewy+BcPeqHDALnsEK2WuzAmpfRJ/b 0QX+TOoWDcW/6hwSyaDOab11xAm+OPTXd1bLOlCxz/I/aTx3f1bCcxgqqJQGxYHs778L vwyOQvPc7tF79TjY0gJXetFEQqKmo+A0oq/YkorYL9slkSCEFf3VbVMbsWmkHhi46mjV SO3LRLQ2Bydaw1uVplRpVTNUqXM26o5POpKun+BWWjoBiHeRe3hVHZoD6hBQWVcrRvGC rdRA== MIME-Version: 1.0 X-Received: by 10.28.6.142 with SMTP id 136mr9825397wmg.9.1446404406323; Sun, 01 Nov 2015 11:00:06 -0800 (PST) Received: by 10.28.183.139 with HTTP; Sun, 1 Nov 2015 11:00:06 -0800 (PST) In-Reply-To: <56365650.1080701@gmail.com> References: <56365650.1080701@gmail.com> Date: Sun, 1 Nov 2015 19:00:06 +0000 Message-ID: From: Andy Talbot To: rsgb_lf_group@blacksheep.org, rsgb_lf_group@yahoogroups.co.uk X-Scan-Signature: 54c274b8b0f8da777e8f702c98fe24ad Subject: Re: LF: RTE 252kHz Content-Type: multipart/alternative; boundary=001a11442706d736e605237f44ad 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: 4771 --001a11442706d736e605237f44ad Content-Type: text/plain; charset=UTF-8 Hi All - Its no good at this stage looking for small signals. All I'm trying to do is prove the HARDWARE. At the moment I have a QSD type receiver delivering a signal centred on 1kHz. This is bandpass filtered to about 100Hz bandwidth, then I/Q sampled at 1kHz sampling rate to deliver 12 bit baseband values at 1kHz At the moment all I'm doing with these is displaying them on a vectorscope plot - like that shown in the attachment - in order to prove phase coherency of the system. So only strong signals are acceptable at this stage - decimation and narrowband filtering can come later - that is high level software and easier to implement And I've discovered something that needs explaining. Having just been monitoring Droitwich on 198kHz for the last couple of hours, its phase plot indicates drift of 300 degrees in that time. Expressed in terms of a frequency offset that is 0.00012Hz, or 0.6 PPB at 198kHz. Now : My reference is a VE2ZAZ GPSDO which is long term spot on, but subject to short term variations. I have to check if it remains better than 0.6PPB over that period. The VE2ZAZ isn't my favourite solution for LF working. But a local high standard frequency reference isn't an issue - the Caesium tube can be turned on to solve that one! The LO in the LF receiver is a DDS tuned by a rotary encoder. The PIC maths was written from first principles using 64 x 64 bit integer arithmetic, BUT the pre-stored -constants to start with were evaluated via a spreadsheet - which I'm not convinced provides sufficient numerical accuracy to simulate the maths resolution needed to get teh constantsin teh first place. So that needs checking. And, of course, although Droitwich is supposed to be a frequency standard, it is only Rubidium controlled; set manually from "time to time" against an on site Caesium source. 0.6 PPB is of the order of a Rb source that hasn't been corrected for a while. Is Droitwich properly maintained these days when very few people want it as a reference? can we really assume its good enough? I've now changed to monitoring MSF 60kHz so lets see what indicted drift that shows - its reasonable to assume that really is good! Checking the constants used in the arithmetic is the most difficult task. My high level programming language only offer up to 64 bit integers, so the multiplication used in the PIC cannot be simulated exactly in a prog, meaning I need to work with double precision floats and cast to integers as and when. Andy G4JNT On 1 November 2015 at 18:13, IZ7SLZ wrote: > On 11/1/2015 4:17 PM, Andy Talbot wrote: > >> Oh well... >> >> Still searching for a clean MF carrier >> >> Andy G4JNt >> >> > Hello Andy, and all > > i'm now putting a small signal on 478502.24 Hz in opera8 mode. Tx is > GPS-locked. It is the same TX exciter that i used in EbNaut experiment > weeks ago. > Maybe this signal is useful for your receiver test. > > All the best. > > 73, Domenico / iz7slz > > --001a11442706d736e605237f44ad Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Hi All -=C2=A0

Its no good at this stag= e looking for small signals.=C2=A0 All I'm trying to do is prove the HA= RDWARE.=C2=A0 At the moment I have a QSD type receiver delivering a signal = centred on 1kHz. =C2=A0 =C2=A0This is bandpass filtered to about 100Hz band= width, then I/Q sampled at 1kHz sampling rate to deliver 12 bit baseband va= lues at 1kHz

At the moment all I'm doing with = these is =C2=A0displaying them on a vectorscope plot - like that shown in t= he attachment - in order to prove phase coherency of the system.=C2=A0 So o= nly strong signals are acceptable at this stage - decimation and narrowband= filtering can come later - that is high level software and easier to imple= ment

And I've discovered something that needs = explaining.=C2=A0 Having just been monitoring Droitwich on 198kHz for the l= ast couple of hours, its phase plot indicates drift of 300 degrees in that = time. =C2=A0 Expressed in terms of a frequency offset that is 0.00012Hz, or= 0.6 PPB at 198kHz.

Now :
My reference i= s a VE2ZAZ GPSDO which is long term spot on, but subject to short term vari= ations. =C2=A0 I have to check if it remains better than 0.6PPB over that p= eriod. =C2=A0 =C2=A0The VE2ZAZ isn't my favourite solution for LF worki= ng.=C2=A0 But a local high standard frequency reference isn't an issue = - the Caesium tube can be turned on to solve that one!

=
The LO in the LF receiver is a DDS tuned by a rotary encoder. =C2=A0 = =C2=A0The PIC maths was written from first principles using 64 x 64 bit int= eger arithmetic, BUT the pre-stored -constants to start with were evaluated= via a spreadsheet - which I'm not convinced provides sufficient numeri= cal accuracy to simulate the maths resolution needed to get teh constantsin= teh first place. =C2=A0 So that needs checking.

A= nd, of course, =C2=A0 although Droitwich is supposed to be a frequency stan= dard, it is only Rubidium controlled; set manually from "time to time&= quot; against an on site Caesium source. =C2=A00.6 PPB is of the order of a= Rb source that hasn't been corrected for a while. =C2=A0 Is Droitwich = properly maintained these days when very few people want it as a reference?= =C2=A0can we really assume its good enough?

I'= ;ve now changed to monitoring MSF 60kHz so lets see what indicted drift tha= t shows - its reasonable to assume that really is good!

Checking the constants used in the arithmetic is the most difficult t= ask.=C2=A0 My high level programming language only offer up to 64 bit integ= ers, so the multiplication used in the PIC cannot be simulated exactly in a= prog, meaning I need to work with double precision floats and cast to inte= gers as and when.

Andy =C2=A0G4JNT

On 1 November 2015 at= 18:13, IZ7SLZ <iz7slz.domenico@gmail.com> wrote:
On 11/1/2015 4:17 PM, Andy Talbot wrote:
Oh well...

Still searching for a clean MF carrier

Andy=C2=A0 =C2=A0G4JNt


Hello Andy, and all

i'm now putting a small signal on 478502.24 Hz in opera8 mode. Tx is GP= S-locked. It is the same TX exciter that i used in EbNaut experiment=C2=A0 = weeks ago.
Maybe this signal is useful for your receiver test.

All the best.

73, Domenico / iz7slz


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