Lux, James P wrote: >> You will need to use high end sound cards like the M-Audio >> AP192 for good performance. >> > > If you're using that particular card , I'd definitely build a new cable for > it. You can probably do better than 1/4" TRS phone plugs. > > I use XLR to TRS cables with it. > > >>> >> Dont forget to have an individual isolation amplifiers >> between each LO port and the LO itself. >> The easiest method is to use a DDS system to generate the >> required offset LO frequency. >> However bandpass filtering of the output is necessary and >> care must be taken to select the DDS clock frequency to >> ensure that the principal phase truncation spur as well as >> other spurs are sufficiently far from the desired output that >> they can easily be filtered out. Use the DDS tools on the >> Analog Devices site to help with this. >> The DDS clock itself needs to have relatively low noise >> either divide 10MHz by 2 and then multiply by 9 to get 45MHz >> which appears appropriate for the AD9850 series chips, or >> build a low noise discrete 45MHz LO. >> > > > You might want to look at the 99xx series DDSes. If nothing else, they run > cooler than the 985x series(AD9854, used in a variety of quadrature schemes, > draws 1.2A @3.3V.. Yep, it gets mighty toasty warm, and needs serious > heatsinking and a fan or it gets intermittent) > > The newer DDSes have lower power, faster clocks, lower spurs, more bits in > the DAC, etc. Although, I'm not sure how important all these things would be > in this application. > > There are also some very low phase noise, low jitter XO available that can > drive these things (not temperature compensated, though, so as the XO temp > changes, so does the frequency) > >
Using a low phase noise XO with a suitable frequency would probably be preferable as there would be fewer potential problems with spurs. With appropriate algorithms the drift in beat frequency with temperature shouldn't be too much of a problem. Bruce _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
