> Next generation transceivers will not use crystal filters > and mixers, they are already appearing and the performance > is outstanding.
If the next generation of transceivers does in fact abandon narrow filtering ahead of the ADC it will be a sorry step backward. While some of the designs like the Flex-5000 and Peresus have excellent specs for the most part when tested against two tone situations, they are still substandard in dealing with multiple very strong in-band signals as would occur on 160/80/75 meters in a contest or on 40 meters with the multiple megapower broadcasters. To maintain linearity, an ADC must be able to withstand the instantaneous peak signal (vector sum - not average) from all the signals within its passband. For some DSR designs that maintain bandwidths from several hundred KHz to 10s of MHz that peak signal handling capability requirement can be significant and represents a required dynamic range orders of magnitude greater than even the best current technology. It is the multi-tone interference that is best handled by narrow filtering ahead of the ADC (e.g., the K3 design). 73, ... Joe, W4TV > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Dave G4AON > Sent: Saturday, November 08, 2008 6:38 AM > To: [email protected] > Subject: Re: [Elecraft] K3 vs. HPSDR Mercury receiver > > > The explanation from the article is as follows: > > "When noise pulses/spikes pass through a crystal > filter, the phase response of the filter > changes, depending on the noise frequency. > However, when noise pulses/spikes pass > through an ADC with a linear response, the > phase response stays the same, because the > ADC treats them in a linear manner." > > While the K3 is "SDR", it also includes crystal roofing filters which > the Mercury does not. My Perseus SDR (which also operates with a high > speed ADC for direct decoding - no crystals or mixers) does deal with > noisy signals better than my K3. > > Next generation transceivers will not use crystal filters and mixers, > they are already appearing and the performance is outstanding. > > 73 Dave, G4AON > K3/100 #80 > ----------------------------------------- > >/ SDR where the authors compare a K3 with a HPSDR Mercury > receiver and />/ explain why the SDR sounds better than the > K3 (noise through a crystal />/ filter causing phase > changes). / The K3 is also an SDR! > > -- > David Woolley > _______________________________________________ > Elecraft mailing list > Post to: [email protected] > 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 _______________________________________________ Elecraft mailing list Post to: [email protected] 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
