Hi The "normal" approach uses twice the frequency so it can generate the quadrature LO by division. If you run two DDS's you don't have to get the quadrature signals that way. You can have them each generate one of the two required phases of the LO directly. I suspect that's why the radio will run up to the top end of the DDS frequency range.
Of course if the Nyquist frequency is 37 and you are at 36.9 you will have a spur at 37.1 to deal with. It'll take a lot more than a third order filter to do that. Bob On Jan 24, 2010, at 5:48 AM, Stephan Schaa wrote: > > Yes, you're right, Diodes make the same, too. :-) > > I was asking because normally this kind of mixers use twice receiving > frequency for downsampling to Baseband. But the DDS goes only up to 37 MHz. > So do you use undersampling with the RX (single balanced mixer, I would call > it "even harmonic reception") ? > If so, is - for example - DRM reception be affected by the loss of > information? > > This is the reason why I asked for the bandpasses, too. Here in europe we > have a lot of strong signals on the air and it's important to use good > bandpasses in these kind of designs to get the harmonics out ( 2x, 3x, 4x ... > in single balanced mixers, 3x, 5x in double balanced mixers) of the receiving > chain. > > Stephan > > > > Von: [email protected] [mailto:[email protected]] Im > Auftrag von ni9n > Gesendet: Sonntag, 24. Januar 2010 11:23 > An: [email protected] > Betreff: [soft_radio] Re: LD-1 Discussion on Garage-shoppe.com Blog > > > > Hi, Stephan! Yes, it uses a Tayloe detector, and the preselector filters are > all third order. > > It's my understaniding that even the classic diode-ring mixers are really > switching mixers, because the diodes in effect hard-limit the LO. In the > frequency domain, using a Tayloe detector (or any switching mixer) sacrifices > nothing as long as the sampling images are filtered out downstream. > > --- In [email protected], "Stephan Schaa" <sc...@...> wrote: > > > > Hello ni9n! > > > > I've a question about your receiver: Do you use a kind of Swichting Mixer, > > sometimes called Tayloe Detector? Or ist it classic single or dual > > conversion? It would be interesting if you would post some more information > > about the bandpasses like which order they are. > > > > 73, Stephan > > >
