One advantage to having a gain stage ahead of the QSD is that you have much better matching between the front end filters and the QSD ... In my SDR testbed I'm using a push-pull pair of 2SC1253's (Similar to the 2N5109) which is one of the few RF preamps that has a high enough IP3 to not degrade the high IP3 of the FST3253 based QSD ... In fact I'm so pleased with the original design I doubt I'll change it other than a couple of minor tweaks
I still think the weak spot in most SDR front ends lies in the circuitry following the QSD, the INA mic preamps and single op-amp diff amps are far from the best choices ... high end audio frequency designs are needed here and you won't find either of these circuits used on anything above a DJ type mixer for several reasons At least amatuer designs are getting away from the LM324's with their horrific crossover distortion ... I still cringe when I see one of those used in any kind of audio circuit JR --- In [email protected], "[EMAIL PROTECTED]" <[EMAIL PROTECTED]> wrote: > > jr_dakota > > Ok, I do like the idea of the gain on the frontend. > > Hey, a bunch from here went and joined HuffPuffVFO also. So they are > investigating that for possiblities. > > ka9rza > > > _____________________________________________________________________ > PrivatePhone - FREE telephone number & voicemail. > A number so private, you can make it public. > http://www.privatephone.com > ------------------------ Yahoo! Groups Sponsor --------------------~--> See what's inside the new Yahoo! Groups email. http://us.click.yahoo.com/2pRQfA/bOaOAA/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/
