At 08:08 PM 11/2/2006, Larry wrote: >Bob, > >I have also been told of a significant carrier presence during SSB transmit. >I have been trying to confirm this. I am also using a Delta 44 card.
Unless the design has changed since the original, the sound card won't make any difference, because of the AC coupling. You're really depending on the matching of the 22 uF capacitors, I think. I would expect the leakage current to be fairly well matched on the mux. A simple test. Try putting a small DC voltage on just I or Q (using a 10K pot and a battery, for instance) and see if you get more carrier. >--Larry W8ER > > >----- Original Message ----- >From: <[EMAIL PROTECTED]> >To: <flexradio@flex-radio.biz> >Sent: Thursday, November 02, 2006 9:09 PM >Subject: [Flexradio] Hey Bob - IQ DC offset hooks > > > > > > > > Hi Bob, > > > > > > > > Is there a way to get at Tx I&Q DC offsets in your code. I couldn't fine > > any. > > > > > > > > Some of the SDR stations on the air have noticeable carrier present during > > SSB TX. > > > > > > > > Using a spectrum analyzer I've noticed that during TX image cancellation I > > can get the image > > > > 20-30 db below the residual carrier! > > > > > > > > After thinking about this I decided to measure the output of my Delta 44 > > sound card. It has offsets of > > > > -12.8mV on the I channel and -4.11mV on the Q. I would imagine some cards > > are worse. > > > > > > > > It would be sweet to null the carrier another 1,000%. > > > > > > > > 73, > > > > John > > > > -------------- next part -------------- > > An HTML attachment was scrubbed... > > URL: > > > /pipermail/flexradio_flex-radio.biz/attachments/20061102/8f0b93a4/attachment.html > > _______________________________________________ > > FlexRadio mailing list > > FlexRadio@flex-radio.biz > > http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz > > Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ > > FlexRadio Homepage: http://www.flex-radio.com > > > > >_______________________________________________ >FlexRadio mailing list >FlexRadio@flex-radio.biz >http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz >Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ >FlexRadio Homepage: http://www.flex-radio.com James Lux, P.E. Spacecraft Radio Frequency Subsystems Group Flight Communications Systems Section Jet Propulsion Laboratory, Mail Stop 161-213 4800 Oak Grove Drive Pasadena CA 91109 tel: (818)354-2075 fax: (818)393-6875 _______________________________________________ FlexRadio mailing list FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archive Link: http://www.mail-archive.com/flexradio%40flex-radio.biz/ FlexRadio Homepage: http://www.flex-radio.com
