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, > Wayne > N6KR > > > > On Jun 4, 2019, at 5:10 PM, Lyle Johnson <kk7p4...@gmail.com> wrote: > > > > Mark, > > > > The "20 dB lower than a K3" figure is an estimate for 100 kHz Blocking > Dynamic Range rather than the 2 kHz Narrow Spaced Dynamic Range. > > > > The K3 is listed at 140 to 150 dB (depending on model, synthesizer, etc) > on Sherwood's Receiver Test Data page. The K4 series without the "HD" > option are estimated to be in the 120 to 130 dB range, typical of other > direct sampling SDR products (Flex, Apache, Icom, ...). > > > > 73, > > > > Lyle KK7P > > > > On 6/4/19 4:00 PM, mark roz via Elecraft wrote: > >> Before putting my money up front for the first run of K4D I need to > know what is the dynamic range > >> of the K4D RX at 2kHz spacing. K3 is 105 dB and K4D? If it is 20dB > lower than K3 than it would be 85dB-correct? > > > > ______________________________________________________________ > 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 richard.corfi...@gmail.com > ______________________________________________________________ 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
