Return-Path: Received: from mtain-mj12.r1000.mx.aol.com (mtain-mj12.r1000.mail.aol.com [172.21.164.96]) by air-dc03.mail.aol.com (v129.4) with ESMTP id MAILINDC033-864f4ccc76fd1cb; Sat, 30 Oct 2010 15:50:21 -0400 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-mj12.r1000.mx.aol.com (Internet Inbound) with ESMTP id 822E538000093; Sat, 30 Oct 2010 15:50:19 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1PCHPs-0006hI-1J for rs_out_1@blacksheep.org; Sat, 30 Oct 2010 20:48:40 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1PCHPr-0006h9-3j for rsgb_lf_group@blacksheep.org; Sat, 30 Oct 2010 20:48:39 +0100 Received: from mail-iw0-f171.google.com ([209.85.214.171]) by relay1.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1PCHPp-00033t-7c for rsgb_lf_group@blacksheep.org; Sat, 30 Oct 2010 20:48:39 +0100 Received: by iwn35 with SMTP id 35so1615305iwn.16 for ; Sat, 30 Oct 2010 12:48:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=googlemail.com; s=gamma; h=domainkey-signature:mime-version:received:received:in-reply-to :references:date:message-id:subject:from:to:content-type; bh=HsDfZS4rAo7x7jynIijYROnBB2QsA4c3V2PqOEK0Ds8=; b=Kd+O0rcbWMwRUYdu9C5DTdM1Y/VVhsz/EMN4Klbjt6h1qkyoCq0NdeKuwrgyHBaboa vRfKK8YS1tNaRz/6ffWvjtt+3tiMf5GddNWtwO0ALw3dvCPkYi0tsQsaaCllq/B/KW3f pnC9SiYal7e5LEDx8pT2gi7sdvORyrKtKAr3I= DomainKey-Signature: a=rsa-sha1; c=nofws; d=googlemail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=FlBZvg+CnFyvliEYIjpIPWIq9xsW0CV8FraUTXWVFSvehwuiWW1UFZ+rq1wdNTvuJB Iml9uF+r4B8MyBIkAxdHkiHkN4qhFiCCau/1SptShZAnk2nse6HWOdb6DrNuf95ifFOo FDFkZkczf9QKk54iv4b/Ru0SLUgWCnBsJ7XF4= MIME-Version: 1.0 Received: by 10.42.221.137 with SMTP id ic9mr414068icb.151.1288468115229; Sat, 30 Oct 2010 12:48:35 -0700 (PDT) Received: by 10.231.79.69 with HTTP; Sat, 30 Oct 2010 12:48:35 -0700 (PDT) In-Reply-To: <00f001cb7865$ad833bc0$0201a8c0@Clemens04> References: <4CCAED49.6030007@o2.ie> <4CCC2277.9040801@o2.ie> <045201cb7844$ca1df020$0201a8c0@Clemens04> <006b01cb7857$f564e870$4001a8c0@lark> <00f001cb7865$ad833bc0$0201a8c0@Clemens04> Date: Sat, 30 Oct 2010 20:48:35 +0100 Message-ID: From: Andy Talbot To: rsgb_lf_group@blacksheep.org 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=20cf30434752500fe70493dadce3 X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.5 required=5.0 tests=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-m273.1 ; domain : googlemail.com DKIM : pass x-aol-sid: 3039400c89b84ccc76fb2034 X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none X-Mailer: Unknown (No Version) --20cf30434752500fe70493dadce3 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable AH, forgot that note only gave the results, and didn't include 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 asymmetry -= was the whole point of making the measurements. It was actually G3PLX who asked me to do them as he didn't have the test equipment. What they sho= w is that the 'classic' third order linearity model is not applicable to direct sampling SDRs 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 products remains *reasonably* constant with varying two-tone input amplitude whereas conventionally you should see a 3dB/dB variation. But then it changes dramatically when a third tone is introduced that *can= not itself contribute to the IP3 tone being measured*. Peter spotted somethi= ng like this and asked me to confirm with the more controlled measurements One explanation we can think of is that there is no "real" third order product being generated at all, certainly not one above the A/D quantisati= on noise, but there is leakage from the digital lines. A single tone int= o the A/D will give signal components on the digital A/D ouptuts that contai= n 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 spectrum= 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 around a lot more, so reducing the level and changing the spectrum of teh leakage. This effect is observed and can be seen in the measurements All a bit empirical but if you web-search on "SDR Linearity" you'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. That will ensure the spectrum of RF leakage from the digital outputs will be noiseli= ke with no discrete components and hence allow higher dynamic range. In othe= r words, just what you see by connecting to an antenna. In fact the very highest specification top end A/D converters do optionall= y deliberately jitter the clock to spread out the leakage spectrum. The jitter is taken out digitally by DSP within the A/D chip itself so the use= r sees a tranparant conversion, or this can be done subsequently by the user if preferred. Probably a perusal of the Analog Devices web site www.analog.com will reveal a plethora of papers on linearity specificatio= ns and results. I believe a formalised route to DD Receiver specification is being develop= ed and prbably has been by now, , but I have had no inclination to follow the story these days - that's all a bit too much like the work I used to do an= d couldn't wait to retire from. Andy www.g4jnt.com On 30 October 2010 20:07, Clemens Paul wrote: > Hello Andy, > > your test results show quite strong differencies 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 inherent IM3 behaviour of your test > setup itself. > 3dB-combiners have only 30-35dB port isolation,true hybrid combiners (6d= B) > are better by at least 20dB,if they are made tunable up to 80dB isolatio= n > is achievable. > Also the 70dB resistive isolation between the two crystal oscillators se= ems > to > be a bit on the short side. > > 73 > Clemens > DL4RAJ > > > > ---- Original Message ----- > > *From:* Andy Talbot > *To:* rsgb_lf_group@blacksheep.org > *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 > > 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 direc= t >> sampling! >> :-)) 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 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 the 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 > Version: 9.0.864 / Virendatenbank: 271.1.1/3227 - Ausgabedatum: 10/30/10 > 08:34:00 > > --20cf30434752500fe70493dadce3 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable
AH,=A0 forgot that=A0note only gave the results, and didn't inclu= de any explanation of the findings...
Perhaps the contents of this email should be added to it
=A0
The complete unpredictability - far more than just the IMP-3 asymmetr= y - was the whole point of making the measurements.=A0=A0 It was actually= G3PLX who asked me to do them as he didn't have the test equipment.= =A0=A0 What they =A0show is that the 'classic' third order lineari= ty model is not applicable to=A0 direct sampling=A0SDRs and high speed A/D= converters and a completely new approach is needed.
=A0
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.
=A0
But then it changes dramatically when a third tone is introduced that= cannot itself contribute to the IP3 tone being measured.=A0=A0= Peter spotted something like this and asked me to confirm with=A0the more= controlled measurements
=A0
One explanation we can think of is that there is no "real"= third order product being generated at all, certainly not one above the= A/D quantisation noise, but there is leakage from the digital lines.=A0= =A0=A0=A0=A0 A single tone into the A/D will give signal=A0components on= the digital A/D ouptuts that contain components at the input frequency an= d=A0 its harmonics, which can leak into the RF path.
=A0
Two tone signals will include I/M sidebands as well within this spect= rum=A0and those on the=A0Lowest Significant Bits=A0will probably remain pr= etty constant whatever the input amplitude, =A0provided it is above the mi= nimum quantising level.=A0 When a third non related tone in intoduced, whatever its level, the LSBs will be jittered around a lot more, so= reducing the level and changing the spectrum of teh leakage.=A0=A0 This= effect is observed and can be seen in the measurements
=A0
All a bit empirical but if you web-search on "SDR Linearity"= ;=A0 you'll find a large number of papers and observations now; many= =A0showing similar results and offering similar conclusions.
=A0
So, in conclusion :-
We cannot use conventional analogue-receiver linearity definitions or= measurement techniques on direct samplibg SDRs.
=A0
What we can safely say, is that direct sampling receivers will work= best in the presence of multiple signals with a spread of amplitudes.=A0= That will ensure the spectrum of RF leakage from the digital outputs will= be noiselike with no discrete components and hence allow higher dynamic= range.=A0 In other words, just what you see by connecting to an antenna.<= /div>
=A0
In fact the very highest=A0specification top end A/D converters do op= tionally deliberately jitter the clock to spread out the leakage spectrum.= =A0 The jitter is taken out digitally by DSP within the A/D chip itself so= the user sees a tranparant conversion, or this can be done subsequently= by the user if preferred.=A0=A0 Probably a perusal of the Analog Devices= web site www.analog.com=A0 will re= veal a plethora of papers on linearity specifications and results.
=A0
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=A0= follow=A0the story=A0these 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,
=A0
your test results show quite strong= differencies between the
upper and lower IM3 product,up to 18d= B.
Unsymmetrical IM3 products=A0*always*= imply=A0 that there is more than one
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 bet= ween the two crystal oscillators seems to
be a bit on the short side.=A0=
=A0
73
Clemens
DL4RAJ
=A0
=A0
=A0
---- Original Message -----
Sent: Saturday, October 30, 2010 7:= 47 PM
Subject: Re: LF: RFspace SDR-IQ

=A0
Showing some of the minor peculiarities of DS SDRs
On 30 October 2010 18:04, Alan Melia <alan.melia@btinternet.com> wrote:
Hi Clemens, you seem to impute= that there are no shortcommings in direct
sampling!
=A0:-)) =A0 =A0= I suspect there are, but they are just "different". =A0You may= be
right about the units mentioned, but it is just as easy to make a poorlypreforming 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 perfor= mance of some units is quite remarkable and I do
own a couple very good= conventional receivers.

Alan G3NYK

----- Original Message -----
From: "Clemens Paul" &l= t;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 =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 sam= pling SDR like those e.g. from RF space or
> Perseus.
>
>= ; 73
> Clemens
> DL4RAJ
>
> ----- Original Message= -----
> From: "Tony" <ei8jk@o2.ie>
> To: <rsgb_lf_group@blacksheep.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 Mond= ay 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 an= y experience with this SDR ?
> >> It looks interesting and I&#= 39;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.
> >&= gt;
> >>
> >>
> >
> >
> >
> -------------------------------------------------------------= -------------
------
>
>
>
> Eingehende eMail= ist virenfrei.
> Von AVG =FCberpr=FCft - www.avg.de
> Version: 9.0.864 / Virendatenbank: 271.1.1/3226 - Ausgabedatum:
&g= t; 10/29/10 20:34:00
>
>


<= /div>


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=


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