Return-Path: Received: from mtain-dc11.r1000.mx.aol.com (mtain-dc11.r1000.mx.aol.com [172.29.64.139]) by air-df08.mail.aol.com (v129.4) with ESMTP id MAILINDF083-5f004ccc7ac531a; Sat, 30 Oct 2010 16:06:29 -0400 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-dc11.r1000.mx.aol.com (Internet Inbound) with ESMTP id 8749C380000AA; Sat, 30 Oct 2010 16:06:27 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1PCHft-0006xq-P9 for rs_out_1@blacksheep.org; Sat, 30 Oct 2010 21:05:13 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1PCHfs-0006xh-TK for rsgb_lf_group@blacksheep.org; Sat, 30 Oct 2010 21:05:12 +0100 Received: from nm8-vm0.bullet.mail.ne1.yahoo.com ([98.138.91.23]) by relay1.thorcom.net with smtp (Exim 4.63) (envelope-from ) id 1PCHfq-0003Bo-FP for rsgb_lf_group@blacksheep.org; Sat, 30 Oct 2010 21:05:12 +0100 Received: from [98.138.90.48] by nm8.bullet.mail.ne1.yahoo.com with NNFMP; 30 Oct 2010 20:05:03 -0000 Received: from [98.138.89.164] by tm1.bullet.mail.ne1.yahoo.com with NNFMP; 30 Oct 2010 20:05:01 -0000 Received: from [127.0.0.1] by omp1020.mail.ne1.yahoo.com with NNFMP; 30 Oct 2010 20:03:58 -0000 X-Yahoo-Newman-Property: ymail-3 X-Yahoo-Newman-Id: 321565.75387.bm@omp1020.mail.ne1.yahoo.com Received: (qmail 1948 invoked by uid 60001); 30 Oct 2010 20:03:57 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yahoo.com; s=s1024; t=1288469037; bh=Aiw1sxhR8mveyUj04K2uK3MKuHmCC7mpadP9gCJqP68=; h=Message-ID:X-YMail-OSG:Received:X-Mailer:References:Date:From:Subject:To:In-Reply-To:MIME-Version:Content-Type; b=IKpAUfL/LMNkoYk6/xigqIQ4YPSNL/QnOS/frHGVWTiaEfPLM0I/IuQQEA3Hd+X7znQ4hsczRcdTFr+aOQJEY13dgLs+jyCU5Sf0nzt+BlbAOGUOJVx580HTfiEJ4r08+8VA06b1tdmMIlrku4+gM+orW+aMCfjN+x3ySQzEGPc= DomainKey-Signature:a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=Message-ID:X-YMail-OSG:Received:X-Mailer:References:Date:From:Subject:To:In-Reply-To:MIME-Version:Content-Type; b=flm7SI1fp9nOY219ab20o3grcYxCJrOXUWQitkewHj0wO69qvE4UdhLQPfQAMqh/+KLB4MENAdQYFpg2FxJftqi5uW+8mhaw2IGhPWfXvRBuJW1W+T3cZg2Pff24fwrX2KI9RP1ch6M4r6A+k9beAJ/xXEAH4FFZdqHc/Bm0yCw=; Message-ID: <642509.98922.qm@web111906.mail.gq1.yahoo.com> X-YMail-OSG: zwGlq08VM1k5x9R.fN39lSZUInogzCFQ0xrjbnXzNPrne27 6ctkOhU48 Received: from [87.11.201.173] by web111906.mail.gq1.yahoo.com via HTTP; Sat, 30 Oct 2010 13:03:57 PDT X-Mailer: YahooMailRC/504.5 YahooMailWebService/0.8.107.284920 References: <4CCAED49.6030007@o2.ie> <4CCC2277.9040801@o2.ie> <045201cb7844$ca1df020$0201a8c0@Clemens04> <006b01cb7857$f564e870$4001a8c0@lark> <00f001cb7865$ad833bc0$0201a8c0@Clemens04> Date: Sat, 30 Oct 2010 13:03:57 -0700 (PDT) From: Daniele Tincani To: rsgb_lf_group@blacksheep.org In-Reply-To: MIME-Version: 1.0 DomainKey-Status: good (testing) X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,HTML_MESSAGE=0.001 Subject: Re: LF: RFspace SDR-IQ Content-Type: multipart/alternative; boundary="0-1877112085-1288469037=:98922" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=1.0 required=5.0 tests=FORGED_YAHOO_RCVD,HTML_20_30, HTML_MESSAGE autolearn=no version=2.63 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-aol-global-disposition: G X-AOL-SCOLL-AUTHENTICATION: mail_rly_antispam_dkim-m243.1 ; domain : yahoo.com DKIM : pass x-aol-sid: 3039ac1d408b4ccc7ac30f53 X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none --0-1877112085-1288469037=:98922 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Hello Andy, I read something related to your discussion here: http://www.sm5bsz.com/dynrange/qex/digital-imd.pdf Best regards Daniele ________________________________ From: Andy Talbot To: rsgb_lf_group@blacksheep.org Sent: Sat, October 30, 2010 9:48:35 PM Subject: Re: LF: RFspace SDR-IQ AH,=A0 forgot that=A0note only gave the results, and didn't include any ex= planation=20 of the findings... Perhaps the contents of this email should be added to it The complete unpredictability - far more than just the IMP-3 asymmetry -= was the=20 whole point of making the measurements.=A0=A0 It was actually G3PLX who as= ked me to=20 do them as he didn't have the test equipment.=A0=A0 What they =A0show is= that the=20 'classic' third order linearity model is not applicable to=A0 direct sampl= ing=A0SDRs=20 and high speed A/D converters and a completely new approach is needed. The fact shows up dramtically when you observe that the level of the third= order=20 products remains reasonably constant with varying two-tone input amplitude= =20 whereas conventionally you should see a 3dB/dB variation. But then it changes dramatically when a third tone is introduced that cann= ot=20 itself contribute to the IP3 tone being measured.=A0=A0 Peter spotted some= thing like=20 this and asked me to confirm with=A0the more controlled measurements One explanation we can think of is that there is no "real" third order pro= duct=20 being generated at all, certainly not one above the A/D quantisation noise= , but=20 there is leakage from the digital lines.=A0=A0=A0=A0=A0 A single tone into= the A/D will=20 give signal=A0components on the digital A/D ouptuts that contain component= s at the=20 input frequency and=A0 its harmonics, which can leak into the RF path. Two tone signals will include I/M sidebands as well within this spectrum= =A0and=20 those on the=A0Lowest Significant Bits=A0will probably remain pretty const= ant=20 whatever the input amplitude, =A0provided it is above the minimum quantisi= ng=20 level.=A0 When a third non related tone in intoduced, whatever its level,= the LSBs=20 will be jittered around a lot more, so reducing the level and changing the= =20 spectrum of teh leakage.=A0=A0 This effect is observed and can be seen in= the=20 measurements All a bit empirical but if you web-search on "SDR Linearity"=A0 you'll fin= d a=20 large number of papers and observations now; many=A0showing similar result= s and=20 offering similar conclusions. So, in conclusion :- We cannot use conventional analogue-receiver linearity definitions or=20 measurement techniques on direct samplibg SDRs. What we can safely say, is that direct sampling receivers will work best= in the=20 presence of multiple signals with a spread of amplitudes.=A0 That will ens= ure the=20 spectrum of RF leakage from the digital outputs will be noiselike with no= =20 discrete components and hence allow higher dynamic range.=A0 In other word= s, just=20 what you see by connecting to an antenna. In fact the very highest=A0specification top end A/D converters do optiona= lly=20 deliberately jitter the clock to spread out the leakage spectrum.=A0 The= jitter is=20 taken out digitally by DSP within the A/D chip itself so the user sees a= =20 tranparant conversion, or this can be done subsequently by the user if=20 preferred.=A0=A0 Probably a perusal of the Analog Devices web site www.ana= log.com=A0=20 will reveal a plethora of papers on linearity specifications and results. I believe a formalised route to DD Receiver specification is being develop= ed and=20 prbably has been by now, , but I have had no inclination to=A0follow=A0the= =20 story=A0these days - that's all a bit too much like the work I used to do= and=20 couldn't wait to retire from. Andy www.g4jnt.com On 30 October 2010 20:07, Clemens Paul wrote: Hello Andy, >=A0 >your test results show quite strong differencies between the >upper and lower IM3 product,up to 18dB. >Unsymmetrical IM3 products=A0*always* imply=A0 that there is more than on= e >IM3 producing source. >Maybe it's a good idea to check the inherent IM3 behaviour of your test >setup itself. >3dB-combiners have only 30-35dB port isolation,true hybrid combiners (6dB= ) >are better by at least 20dB,if they are made tunable up to 80dB isolation >is=A0achievable. >Also the 70dB resistive isolation between the two crystal oscillators see= ms to >be a bit on the short side.=A0 >=A0 >73 >Clemens >DL4RAJ > >=A0 >=A0 >---- Original Message -----=20 >From: Andy Talbot=20 >>To: rsgb_lf_group@blacksheep.org=20 >>Sent: Saturday, October 30, 2010 7:47 PM >>Subject: Re: LF: RFspace SDR-IQ >> >> >>http://www.g4jnt.com/SDRIQ_Linearity.pdf >> >>Showing some of the minor peculiarities of DS SDRs=20 >> >>Andy >>www.g4jnt.com >> >> >> >>On 30 October 2010 18:04, Alan Melia wrote: >> >>Hi Clemens, you seem to impute that there are no shortcommings in direct >>>sampling! >>>=A0:-)) =A0 =A0I suspect there are, but they are just "different". =A0Y= ou may be >>>right about the units mentioned, but it is just as easy to make a poorl= y >>>preforming DSP radio as to make a poor analogue one. We are in danger= of >>>being conditioned to accept that "digital" is the magic dust that solve= s all >>>problems......it is definitely not so! >>> >>>Having said that, the performance of some units is quite remarkable and= I do >>>own a couple very good conventional receivers. >>> >>>Alan G3NYK >>> >>> >>>----- Original Message ----- >>>From: "Clemens Paul" >>>To: >>> >>>Sent: Saturday, October 30, 2010 4:11 PM >>>Subject: Re: LF: RFspace SDR-IQ >>> >>> >>>> Tony, >>>> >>>> the most important difference between SDR-IQ/-IP(from RF Space) >>>> or Perseus and the $200 SDR on >>>> http://www.lazydogengineering.com/LD-1A_SDR.html >>>> is that =A0the latter is no direct sampling receiver. >>>> It uses a downconverting technique with a number of shortcomings,e.g. >>>> phase noise of the LO and others. >>>> I would go for a direct sampling SDR like those e.g. from RF space or >>>> Perseus. >>>> >>>> 73 >>>> Clemens >>>> DL4RAJ >>>> >>>> ----- Original Message ----- >>>> From: "Tony" >>>> To: >>>> Sent: Saturday, October 30, 2010 3:49 PM >>>> Subject: Re: LF: RFspace SDR-IQ >>>> >>>> >>>> > Thanks guys. >>>> > >>>> > You have just tipped the balance for me and I shall be placing an >>>> > order >>>> > for one on Monday morning. >>>> > It's about time I joined the 21st century, but it will be >>>> > interesting to >>>> > compare it to my beloved FT 102 rx. >>>> > >>>> > Tony, EI8JK. >>>> > >>>> > >>>> > On 29/10/2010 16:50, Tony wrote: >>>> >> Hello group. >>>> >> >>>> >> Has anyone any experience with this SDR ? >>>> >> It looks interesting and I'm a bit tempted, especially as it works >>>> >> full spec down to 500 Hz and "usable" to 100 Hz. >>>> >> But as I have never used an SDR, I haven't got a clue if it's any >>>> >> good >>>> >> or not. >>>> >> >>>> >> >>>> >> >>>> > >>>> > >>>> >>>> >>>> ---------------------------------------------------------------------= ----- >>>------ >>>> >>>> >>>> >>>> Eingehende eMail ist virenfrei. >>>> Von AVG =FCberpr=FCft - www.avg.de >>>> Version: 9.0.864 / Virendatenbank: 271.1.1/3226 - Ausgabedatum: >>>> 10/29/10 20:34:00 >>>> >>>> >>> >>> >>> >> ________________________________ >>Eingehende eMail ist virenfrei. >>Von AVG =FCberpr=FCft - www.avg.de=20 >>Version: 9.0.864 / Virendatenbank: 271.1.1/3227 - Ausgabedatum: 10/30/10= =20 >>08:34:00=20 >> >> =20 --0-1877112085-1288469037=:98922 Content-Type: text/html; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable
Hello Andy, I read something related to your discussion here:<= /DIV>
Best regards
Daniele
=
From: Andy Talbot <andy= .g4jnt@googlemail.com>
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: RFspace SDR-IQ
AH,  forgot that note only gave the results, and didn't inc= lude any explanation of the findings...
Perhaps the contents of this email should be added to it
 
The complete unpredictability - far more than just the IMP-3 asymmetr= y - was the whole point of making the measurements.   It was act= ually G3PLX who asked me to do them as he didn't have the test equipment.&= nbsp;  What they  show is that the 'classic' third order lineari= ty model is not applicable to  direct sampling SDRs and high spe= ed A/D converters and a completely new approach is needed.
 
The fact shows up dramtically when you observe that the level of the= third order products remains reasonably constant with varying tw= o-tone input amplitude whereas conventionally you should see a 3dB/dB vari= ation.
 
But then it changes dramatically when a third tone is introduced that= cannot itself contribute to the IP3 tone being measured. &n= bsp; Peter spotted something like this and asked me to confirm with t= he more controlled measurements
 
One explanation we can think of is that there is no "real" third orde= r product being generated at all, certainly not one above the A/D quantisa= tion noise, but there is leakage from the digital lines.   =    A single tone into the A/D will give signal components= on the digital A/D ouptuts that contain components at the input frequency= and  its harmonics, which can leak into the RF path.
 
Two tone signals will include I/M sidebands as well within this spect= rum and those on the Lowest Significant Bits will probably= remain pretty constant whatever the input amplitude,  provided it is= above the minimum quantising level.  When a third non related tone= in intoduced, whatever its level, the LSBs will be jittered arou= nd a lot more, so reducing the level and changing the spectrum of teh leak= age.   This effect is observed and can be seen in the measuremen= ts
 
All a bit empirical but if you web-search on "SDR Linearity"  yo= u'll find a large number of papers and observations now; many showing= similar results and offering similar conclusions.
 
So, in conclusion :-
We cannot use conventional analogue-receiver linearity definitions or= measurement techniques on direct samplibg SDRs.
 
What we can safely say, is that direct sampling receivers will work= best in the presence of multiple signals with a spread of amplitudes.&nbs= p; That will ensure the spectrum of RF leakage from the digital outputs wi= ll be noiselike with no discrete components and hence allow higher dynamic= range.  In other words, just what you see by connecting to an antenn= a.
 
In fact the very highest specification top end A/D converters do= optionally deliberately jitter the clock to spread out the leakage spectr= um.  The jitter is taken out digitally by DSP within the A/D chip its= elf so the user sees a tranparant conversion, or this can be done subseque= ntly by the user if preferred.   Probably a perusal of the Analo= g Devices web site www.analog.com  will reveal a plethora of papers on li= nearity specifications and results.
 
I believe a formalised route to DD Receiver specification is being de= veloped and prbably has been by now, , but I have had no inclination to&nb= sp;follow the story these days - that's all a bit too much like= the work I used to do and couldn't wait to retire from.
On 30 October 2010 20:07, Clemens Paul <cpaul@gmx.net> wrote:
Hello Andy,
 
your test results show quite strong diffe= rencies between the
upper and lower IM3 product,up to 18dB.
Unsymmetrical IM3 products *always*= imply  that there is more than one
IM3 producing source.
Maybe it's a good idea to check the inher= ent IM3 behaviour of your test
setup itself.
3dB-combiners have only 30-35dB port isol= ation,true hybrid combiners (6dB)
are better by at least 20dB,if they are= made tunable up to 80dB isolation
is achievable.
Also the 70dB resistive isolation between= the two crystal oscillators seems to
be a bit on the short side. <= /DIV>
 
73
Clemens
DL4RAJ
 
 
 
---- Original Message -----
Sent: Saturday, October 30, 2010 7:= 47 PM
Subject: Re: LF: RFspace SDR-IQ

http://www.g4jnt.com/SDRIQ_Linearity.pdf
 
Showing some of the minor peculiarities of DS SDRs
On 30 October 2010 18:04, Alan Melia <alan.melia@btintern= et.com> wrote:
Hi Clemens, you seem to impute= that there are no shortcommings in direct
sampling!
 :-)) &nbs= p;  I suspect there are, but they are just "different".  You may= be
right about the units mentioned, but it is just as easy to make a= poorly
preforming DSP radio as to make a poor analogue one. We are in= danger of
being conditioned to accept that "digital" is the magic dust= that solves all
problems......it is definitely not so!

Having= said that, the performance of some units is quite remarkable and I do
= own a couple very good conventional receivers.

Alan G3NYK

----- Original Message -----
From: "Clemens Paul" <cpaul@gmx.net>
To: <rsgb_lf_group@blacksheep.org>
Sent: Saturday, October 30, 2010 4:11 PM
Subject: Re: LF: RFspace= SDR-IQ


> Tony,
>
> the most important differenc= e between SDR-IQ/-IP(from RF Space)
> or Perseus and the $200 SDR on=
> http://www.lazydogengineering.com/LD-1A_SDR.html
> is that=  the latter is no direct sampling receiver.
> It uses a downco= nverting technique with a number of shortcomings,e.g.
> phase noise= of the LO and others.
> I would go for a direct sampling SDR like= those e.g. from RF space or
> Perseus.
>
> 73
>= Clemens
> DL4RAJ
>
> ----- Original Message -----
&g= t; From: "Tony" <ei8jk@o2.ie>
> To:= <rsgb_lf_group@bl= acksheep.org>
> Sent: Saturday, October 30, 2010 3:49 PM
> Subject: Re: LF: RFspace= SDR-IQ
>
>
> > Thanks guys.
> >
> >= ; You have just tipped the balance for me and I shall be placing an
>= ; > order
> > for one on Monday morning.
> > It's abo= ut time I joined the 21st century, but it will be
> > interesting= to
> > compare it to my beloved FT 102 rx.
> >
>= > Tony, EI8JK.
> >
> >
> > On 29/10/2010 16= :50, Tony wrote:
> >> Hello group.
> >>
> &g= t;> Has anyone any experience with this SDR ?
> >> It looks= interesting and I'm a bit tempted, especially as it works
> >>= ; full spec down to 500 Hz and "usable" to 100 Hz.
> >> But as= I have never used an SDR, I haven't got a clue if it's any
> >&g= t; good
> >> or not.
> >>
> >>
> >>
> >
> >
>
>
> --------------= ------------------------------------------------------------
------
= >
>
>
> Eingehende eMail ist virenfrei.
> Von= AVG =FCberpr=FCft - www.avg.de
> Version: 9.0.864 / Virendatenbank: 271.1.= 1/3226 - Ausgabedatum:
> 10/29/10 20:34:00
>
>



Eingehende eMail ist virenfrei.
Von AVG =FCberpr=FCft - www.avg.de=
Version: 9.0.864 / Virendatenbank: 271.1.1/3227 - Ausgabedatum: 10/30= /10 08:34:00


<= br> --0-1877112085-1288469037=:98922--