Direct sampling has no image issues. Sent from my iPad
> On Jun 5, 2019, at 3:23 AM, Richard Corfield <[email protected]> > wrote: > > I'd have thought that superhet would always have the advantage of improved > image rejection due to the IF band filtering. It would also allow ADCs and > associated processing to run slower or lower down in relation to its > Nyquist frequency so allowing for more detail in the sampled signal. Also > can narrow band analogue filtering beat the dynamic range of the ADC? If > its top 10 bits are taken up handling that huge strong signal in its input > passband then you've got fewer bits left for your signal of interest. So > both high bit depth and high sample rate in comparison to signal are harder > to achieve. > > The opposing view being the cost of achieving a high quality Superhet > conversion? If direct sampling and high speed signal processing (FPGA?) can > achieve the results so much more cheaply and simply and reliably? Like the > Class D amplifier in reverse. > > - Richard (M0RJC) > > >> On Wed, 5 Jun 2019 at 03:19, Wayne Burdick <[email protected]> wrote: >> >> The superhet module buys a lot of BDR improvement. But also -- a subtlety >> I've failed to mention so far -- the superhet module is intended to >> somewhat improve 2 kHz IMDDR3 *and* make this figure more repeatable. >> >> Q: Say what? >> >> A: As Rob Sherwood noted many times before finally immortalizing this >> point in his must-read footnotes, A-to-D converters sharing the same part >> number are not all created equal. The long-time previous occupant of his >> Top Spot benefitted from a never-corroborated monotonicity in its ADC's >> LSBs. An act of god. The product of a very good day at the silicon foundry >> when, serendipitously, all the bunny suits were defect-free, and no one was >> exhaling molecules of grain alcohol or other substances from the night >> before. >> >> That said, most ops can get by without the extra BDR and IMDDR3, because >> they're not situated in the RF equivalent of the Gulf Stream. Hence the >> different K4 models. >> >> 73, > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
