I'm two months late with my comment but... I don't think the AD9446 is as bad as Alberto made out. According to the features list it is capable of 100dB 2-tone 3rd order SFDR, though there are no details or figures in the preliminary datasheet to support this claim. The SNR or ENOB of the device will not be a limitation in the few kHz bandwidth of the final filter since there will be a processing gain of > 30dB.
On the other hand the performance quoted in the SDR-1000 review is not exceptional if the 2-tone 3rd order IMD dynamic range is only 97-99dB with a 500Hz filter bandwidth. Restating that to the normal 2.5kHz bandwidth gives a dynamic range of 93dB. However, the fact that it is that good to within 2kHz of the 500Hz filter is impressive. The review indicates that the DR is flat beyond 2kHz which struck me as surprising. I would have expected that beyond 100kHz or so the LPF on the output of the QSD would shield the sound card from strong signals and the QSD itself or the preamps would become the limiting factor. Of course, I'd have to agree with Bob's comment that it is far easier to get the direct conversion + audio SDR approach to work (well) than the high speed A/D + DDC. Nick, G4JNX. Robert McGwier wrote: >Tayloe, Asbrink, and Youngblood have all understood how difficult this >is to use and get good performance. As such the Tayloe's unbalanced or >the Asbrink/Youngblood balanced designs get us nearly there with large >dynamic range and extremely good linearity. These circuits are sample >and hold circuits. With some attention to detail, this is all we need >and it will be much easier to attend to than dealing with 100 msps 16 >bit A/D's. The recent ARRL review (to be published in the October >issue) show that the recently modified SDR-1000 front end has the best >dynamic range at 2 kHz of ANY receiver ever measured by the ARRL or the >Sherwood site or anywhere else that I can find for that matter. The >SDR-1000 2 kHz dynamic range is as good as the Elecraft K2, IC 7800, >and Orion 20 Khz dynamic range numbers! > >I believe strongly that these simple circuits make these high speed >A/D's unnecessary for narrow band applications where narrow band means >up to 100 kHz (!) for frequencies up to 6 meters and maybe beyond. >Given this, the thing to do in my opinion, is to figure out how to push >these clock generation spurs down and to push the high speed A/D's well >into the background for the foreseeable future unless we need close to >MHz wide signalling. > >http://www.flex-radio.com/articles_files/2005-10_QST_Review.pdf > > >Bob >N4HY > > >i2phd wrote: > > > >>The ideal SDR has the antenna directly connected to the ADC, and from >>there on all is done is software. We are not quite at that point yet, >>bit this new ADC from Analog Devices is a step in that direction... >> >>http://www.responses.com/emw/380/9446.html?c=63r9t >> >>Its dynamic range (80 - 85 db of SFDR) is not enough to allow the >>above, but could be useable, at least at an experimentation level, >>preceding the ADC with an AGC-controlled front end (with all the >>disadvantages that such a solution implies...) >> >>73 Alberto I2PHD >> >> >> >> >> >> >>Yahoo! Groups Links >> >> >> >> >> >> >> >> >> >> >> >> >> > > > > > >Yahoo! Groups Links > > > > > > > ------------------------ Yahoo! Groups Sponsor --------------------~--> Get fast access to your favorite Yahoo! Groups. Make Yahoo! your home page http://us.click.yahoo.com/dpRU5A/wUILAA/yQLSAA/ELTolB/TM --------------------------------------------------------------------~-> Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/soft_radio/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
