On Tue, Dec 2, 2008 at 10:27 AM, David Woolley (E.L) <[EMAIL PROTECTED]> wrote: > Philip Covington wrote: >> >> On Tue, Dec 2, 2008 at 8:05 AM, David Woolley (E.L) > >> >> It may seem that way to you, but in real life it turns out the the DDS >> generates spurs due to only approximating a sin function, clock >> leakage, number of bits, etc... There is not the same issue in the > > There is no fundamental reason why the the DDS sine function should be any > worse than the DSP one, nor for it to have any less bits than that with > which the signal is digitised. > > It might be that commonly used DDS chips are rather old technology, and you > are comparing state of the art DSP with ten year old DDS.
Not really. While there is no fundamental reason, we have to deal with what hardware DDS chips are available to designers with their 32/48 bit accumulators and their 10/12/14 bit DACs. Even the very latest DDS chips from Analog (ex. AD9910, AD9912), while better than the older DDS chips by far, still have spurs at certain programmed frequencies if using a very good low phase noise 1 GHz clock and if you use the internal PLL to multiply up to the 1 GHz clock rate still have phase noise issues. -- Phil Covington Software Radio Laboratory LLC Columbus, Ohio http://www.srl-llc.com _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
