I was getting confused momentarily with Direct Conversion :-) On Wed, 5 Jun 2019 at 13:23, W2xj <w...@w2xj.net> wrote:
> Direct sampling has no image issues. > > Sent from my iPad > > > On Jun 5, 2019, at 3:23 AM, Richard Corfield <richard.corfi...@gmail.com> > 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 <n...@elecraft.com> 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:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
