Gary, That part has nothing to do with the filtering - the next step is to convert both the I and Q signals to digital and do the manipulation mathematically - that includes filtering, detection, and most other signal processing functions. The result is then converted to an analog audio signal for the final amplification.
Yes, the amount of flexibility is limited only by the amount of DSP code and speed of the DSP processing - all manner of "magic" can be performed once the signal is placed into the digital "number soup". That is the normal process for a Software Defined Radio - some use a computer soundcard to do the digital/analog conversion and the processor does the computation, but there is no reason why that process cannot be done using a dedicated processor. The K3 already works the same way, but the frequency for the ADC is higher - that really makes little difference. Using the mixer to convert directly to baseband is quite common in SDR receivers. While we are getting close to the time when direct digital sampling from the antenna is feasible, it is not yet available at a price we would want to pay. 73, Don W3FPR On 7/26/2011 11:43 AM, Gary D Krause wrote: > Thanks for the explanation, Alan. So, my next question is, how does it compare > with a crystal filter? It is better? Does it give you more flexibility with > filtering? > > Thanks, > Gary, N7HTS > > > On Tue, 26 Jul 2011 08:08:38 -0700 > Alan Bloom<n...@sonic.net> wrote: > > On Tue, 2011-07-26 at 08:44 -0600, Gary D Krause wrote: > > I've been wondering what Quadarature down-sampling is? This is the > first that I have heard of it. > > > It's like a two-channel direct-conversion receiver. The two channels > are on the same frequency but use local oscillators that are 90 degrees > out of phase. With suitable processing, the in-phase (I) and quadrature > (Q) mixer outputs give both the amplitude and phase of the signal. > Among other things, that makes it possible to suppress the unwanted > sideband of an SSB signal without a crystal filter. > > Alan N1AL > > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
