--- In [email protected], "Chris Hirt" <[EMAIL PROTECTED]> wrote: > [...] > independently -> ISB --???--> AM > [...]
Chris, the problem with independently recovering the upper and the lower sidebands, then summing them to obtain a full AM demodulation (as SDRadio does in ECSS mode), is that you must lock the LO used for the final conversion to baseband to the carrier of the AM signal, otherwise you will have bad distortion. The technique used in SDRadio is not so easily replicable in hardware...basically after the conversion the tan(Q/I) is computed and averaged on each buffer. This represent the instantaneous phase difference between the LO and the signal carrier. The goal is to keep this phase difference constant, which means that the two frequency are equals. Any variation in this phase difference is applied to a very simple PID controller (actually the D part is missing, so it is a PI controller) whose output is used to steer the LO frequency in the right direction. In software all of this means, let's say, maybe a hundred lines of code. In hardware I guess it would be much more complicated... 73 Alberto I2PHD ------------------------ 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/
