Return-Path: Received: from mtain-dj06.r1000.mx.aol.com (mtain-dj06.r1000.mail.aol.com [172.19.187.142]) by air-ma10.mail.aol.com (v129.4) with ESMTP id MAILINMA101-b53c4ccc7aa8291; Sat, 30 Oct 2010 16:06:00 -0400 Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by mtain-dj06.r1000.mx.aol.com (Internet Inbound) with ESMTP id 6C6E6380000A9; Sat, 30 Oct 2010 16:05:58 -0400 (EDT) Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1PCHfE-0006xT-NU for rs_out_1@blacksheep.org; Sat, 30 Oct 2010 21:04:32 +0100 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1PCHfD-0006xG-KN for rsgb_lf_group@blacksheep.org; Sat, 30 Oct 2010 21:04:31 +0100 Received: from mailout-de.gmx.net ([213.165.64.23] helo=mail.gmx.net) by relay1.thorcom.net with smtp (Exim 4.63) (envelope-from ) id 1PCHfB-0003BN-6Q for rsgb_lf_group@blacksheep.org; Sat, 30 Oct 2010 21:04:31 +0100 Received: (qmail invoked by alias); 30 Oct 2010 20:04:22 -0000 Received: from p5DD3411C.dip.t-dialin.net (EHLO Clemens04) [93.211.65.28] by mail.gmx.net (mp063) with SMTP; 30 Oct 2010 22:04:22 +0200 X-Authenticated: #17214767 X-Provags-ID: V01U2FsdGVkX1+QUVYHXQOQ0XS6ixQJKqtOcYUCVRVwBM1QKr120r 9Pyoe1Zj8JKjIb Message-ID: <005e01cb786d$a4ca97a0$0201a8c0@Clemens04> From: "Clemens Paul" To: References: <4CCAED49.6030007@o2.ie><4CCC2277.9040801@o2.ie><045201cb7844$ca1df020$0201a8c0@Clemens04><006b01cb7857$f564e870$4001a8c0@lark><00f001cb7865$ad833bc0$0201a8c0@Clemens04> Date: Sat, 30 Oct 2010 22:04:18 +0200 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3664 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3664 X-Y-GMX-Trusted: 0 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="----=_NextPart_000_005A_01CB787E.66306090" 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-sid: 3039cdbc9d0b4ccc7aa62504 X-AOL-IP: 195.171.43.25 X-AOL-SPF: domain : blacksheep.org SPF : none ------=_NextPart_000_005A_01CB787E.66306090 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable >Perhaps the contents of this email should be added to it Most certainly it would be worth. 73 Clemens DL4RAJ ----- Original Message -----=20 From: Andy Talbot To: rsgb_lf_group@blacksheep.org Sent: Saturday, October 30, 2010 9:48 PM Subject: Re: LF: RFspace SDR-IQ AH, forgot that note only gave the results, and didn't include any= explanation of the=20 findings... Perhaps the contents of this email should be added to it The complete unpredictability - far more than just the IMP-3 asymmet= ry - was the whole point=20 of making the measurements. It was actually G3PLX who asked me to do= them as he didn't have=20 the test equipment. What they show is that the 'classic' third orde= r linearity model is not=20 applicable to direct sampling SDRs and high speed A/D converters and= a completely new approach=20 is needed. The fact shows up dramtically when you observe that the level of the= third order products=20 remains reasonably constant with varying two-tone input amplitude wher= eas conventionally you=20 should see a 3dB/dB variation. But then it changes dramatically when a third tone is introduced tha= t cannot itself contribute=20 to the IP3 tone being measured. Peter spotted something like this an= d asked me to confirm with=20 the more controlled measurements One explanation we can think of is that there is no "real" third ord= er product being generated=20 at all, certainly not one above the A/D quantisation noise, but there= is leakage from the=20 digital lines. A single tone into the A/D will give signal compon= ents on the digital A/D=20 ouptuts that contain components at the input frequency and its harmon= ics, which can leak into=20 the RF path. Two tone signals will include I/M sidebands as well within this spec= trum and those on the=20 Lowest Significant Bits will probably remain pretty constant whatever= the input amplitude,=20 provided it is above the minimum quantising level. When a third non= related tone in intoduced,=20 whatever its level, the LSBs will be jittered around a lot more, so re= ducing the level and=20 changing the spectrum of teh leakage. This effect is observed and ca= n be seen in the=20 measurements All a bit empirical but if you web-search on "SDR Linearity" you'll= find a large number of=20 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=20 on direct samplibg SDRs. What we can safely say, is that direct sampling receivers will work= best in the presence of=20 multiple signals with a spread of amplitudes. That will ensure the sp= ectrum of RF leakage from=20 the digital outputs will be noiselike with no discrete components and= hence allow higher dynamic=20 range. In other words, just what you see by connecting to an antenna. In fact the very highest specification top end A/D converters do opt= ionally deliberately=20 jitter the clock to spread out the leakage spectrum. The jitter is ta= ken out digitally by DSP=20 within the A/D chip itself so the user sees a tranparant conversion,= or this can be done=20 subsequently by the user if preferred. Probably a perusal of the Ana= log Devices web site=20 www.analog.com will reveal a plethora of papers on linearity specific= ations and results. I believe a formalised route to DD Receiver specification is being= developed and prbably has=20 been by now, , but I have had no inclination to follow the story these= days - that's all a bit=20 too much like the work I used to do and 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 combine= rs (6dB) are better by at least 20dB,if they are made tunable up to 80dB is= olation is achievable. Also the 70dB resistive isolation between the two crystal oscillat= ors seems to be a bit on the short side. 73 Clemens DL4RAJ ---- Original Message -----=20 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 direct 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 mak= e 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 remar= kable 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 Spa= ce) > 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 shortcom= ings,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 pla= cing 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 - Ausgabedat= um: > 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 ----------------------------------------------------------------------= -------- Eingehende eMail ist virenfrei. Von AVG =FCberpr=FCft - www.avg.de Version: 9.0.864 / Virendatenbank: 271.1.1/3227 - Ausgabedatum: 10/3= 0/10 08:34:00 ------=_NextPart_000_005A_01CB787E.66306090 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
>Perhaps the contents of this email should be added to it
 
Most certainly it would be worth.
 
73
Clemens
DL4RAJ
<= /DIV>
----- Original Message -----
From:=20 Andy Talbot
Sent: Saturday, October 30,= 2010 9:48=20 PM
Subject: Re: LF: RFspace SDR-= IQ

AH,  forgot that note only gave the results, and didn= 't include=20 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 as= ymmetry -=20 was the whole point of making the measurements.   It was= actually=20 G3PLX who asked me to do them as he didn't have the test=20 equipment.   What they  show is that the 'classic' th= ird order=20 linearity model is not applicable to  direct sampling SDRs= and high=20 speed A/D converters and a completely new approach is needed.
 
The fact shows up dramtically when you observe that the level= of the=20 third order products remains reasonably constant with varyi= ng=20 two-tone input amplitude whereas conventionally you should see a 3dB= /dB=20 variation.
 
But then it changes dramatically when a third tone is introduce= d that=20 cannot itself contribute to the IP3 tone being measured.&nb= sp; =20 Peter spotted something like this and asked me to confirm with = the more=20 controlled measurements
 
One explanation we can think of is that there is no "real" thir= d order=20 product being generated at all, certainly not one above the A/D quan= tisation=20 noise, but there is leakage from the digital=20 lines.      A single tone into the A/D will= give=20 signal components on the digital A/D ouptuts that contain compo= nents at=20 the input frequency and  its harmonics, which can leak into the= RF=20 path.
 
Two tone signals will include I/M sidebands as well within this= =20 spectrum and those on the Lowest Significant Bits wil= l probably=20 remain pretty constant whatever the input amplitude,  provided= it is=20 above the minimum quantising level.  When a third non related= tone in=20 intoduced, whatever its level, the LSBs will be jittered ar= ound a lot=20 more, so reducing the level and changing the spectrum of teh=20 leakage.   This effect is observed and can be seen in the= =20 measurements
 
All a bit empirical but if you web-search on "SDR Linearity"&nb= sp; you'll=20 find a large number of papers and observations now; many showin= g similar=20 results and offering similar conclusions.
 
So, in conclusion :-
We cannot use conventional analogue-receiver linearity definiti= ons or=20 measurement techniques on direct samplibg SDRs.
 
What we can safely say, is that direct sampling receivers will= work best=20 in the presence of multiple signals with a spread of amplitudes.&nbs= p; That=20 will ensure the spectrum of RF leakage from the digital outputs will= be=20 noiselike with no discrete components and hence allow higher dynamic= =20 range.  In other words, just what you see by connecting to an= =20 antenna.
 
In fact the very highest specification top end A/D convert= ers do=20 optionally deliberately jitter the clock to spread out the leakage= =20 spectrum.  The jitter is taken out digitally by DSP within the= A/D chip=20 itself so the user sees a tranparant conversion, or this can be done= =20 subsequently by the user if preferred.   Probably a perusa= l of the=20 Analog Devices web site www.a= nalog.com  will reveal a plethora=20 of papers on linearity specifications and results.
 
I believe a formalised route to DD Receiver specification is be= ing=20 developed and prbably has been by now, , but I have had no inclinati= on=20 to follow the story these days - that's all a bit too= much like=20 the work I used to do and couldn't wait to retire from.
On 30 October 2010 20:07, Clemens Paul <cpaul@gmx.net= >=20 wrote:
Hello Andy,
 
your test results show quite stro= ng=20 differencies between the
upper and lower IM3 product,up to= =20 18dB.
Unsymmetrical IM3 products *= always*=20 imply  that there is more than one
IM3 producing source.
Maybe it's a good idea to check= the inherent=20 IM3 behaviour of your test
setup itself.
3dB-combiners have only 30-35dB= port=20 isolation,true hybrid combiners (6dB)
are better by at least 20dB,if th= ey are made=20 tunable up to 80dB isolation
is achievable.
Also the 70dB resistive isolation= between the=20 two crystal oscillators seems to
be a bit on the short side. 
 
73
Clemens
DL4RAJ
 
 
 
---- Original Message -----
To: rsgb_lf_group@blacksheep.org
Sent: Saturday, October= 30, 2010 7:47=20 PM
Subject: Re: LF: RFspace= SDR-IQ

 
Showing some of the minor peculiarities of DS SDRs
On 30 October 2010 18:04, Alan Melia <alan.melia@btinternet.com> wrot= e:
Hi=20 Clemens, you seem to impute that there are no shortcommings in= =20 direct
sampling!
 :-))    I suspect there= are, but=20 they are just "different".  You may be
right about the= units=20 mentioned, but it is just as easy to make a poorly
preformi= ng DSP=20 radio as to make a poor analogue one. We are in danger of
b= eing=20 conditioned to accept that "digital" is the magic dust that so= lves=20 all
problems......it is definitely not so!

Having sa= id that,=20 the performance of some units is quite remarkable and I do
= own a=20 couple very good conventional receivers.

Alan G3NYK

----- Original Message -----
From: "Clemens Paul"= <cpaul@= gmx.net>
To:=20 <rsgb_lf_group@blacksheep.org>
Sent: Saturday, October 30, 2010 4:11 PM
Subject: Re:= LF:=20 RFspace SDR-IQ


> Tony,
>
> the most= important=20 difference between SDR-IQ/-IP(from RF Space)
> or Perseu= s and the=20 $200 SDR on
> http://www.lazy= dogengineering.com/LD-1A_SDR.html
>=20 is that  the latter is no direct sampling receiver.
&g= t; It uses=20 a downconverting technique with a number of shortcomings,e.g.<= BR>>=20 phase noise of the LO and others.
> I would go for a dir= ect=20 sampling SDR like those e.g. from RF space or
>=20 Perseus.
>
> 73
> Clemens
>=20 DL4RAJ
>
> ----- Original Message -----
> Fr= om: "Tony"=20 <e= i8jk@o2.ie>
> To: <rsgb_lf_group@blacksh= eep.org>
> Sent:=20 Saturday, October 30, 2010 3:49 PM
> Subject: Re: LF: RF= space=20 SDR-IQ
>
>
> > Thanks guys.
> ><= BR>>=20 > You have just tipped the balance for me and I shall be pl= acing=20 an
> > order
> > for one on Monday morning.<= BR>>=20 > It's about time I joined the 21st century, but it will be=
>=20 > interesting to
> > compare it to my beloved FT= 102=20 rx.
> >
> > Tony, EI8JK.
> >
>= ;=20 >
> > On 29/10/2010 16:50, Tony wrote:
> >= ;>=20 Hello group.
> >>
> >> Has anyone any= experience=20 with this SDR ?
> >> It looks interesting and I'm= a bit=20 tempted, especially as it works
> >> full spec dow= n to 500=20 Hz and "usable" to 100 Hz.
> >> But as I have neve= r used an=20 SDR, I haven't got a clue if it's any
> >> good>=20 >> or not.
> >>
> >>
>=20 >>
> >
> >
>
>
>=20 --------------------------------------------------------------= ------------
------
>
>
>
>=20 Eingehende eMail ist virenfrei.
> Von AVG =FCberpr=FCft= - www.avg.de=
> Version:=20 9.0.864 / Virendatenbank: 271.1.1/3226 - Ausgabedatum:
>= 10/29/10=20 20:34:00
>
>


<= /DIV>


Eingehende eMail ist virenfrei.
Von AVG =FCberpr= =FCft - www.avg= .de
Version:=20 9.0.864 / Virendatenbank: 271.1.1/3227 - Ausgabedatum: 10/30/10= 08:34:00=20



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
------=_NextPart_000_005A_01CB787E.66306090--