The K4 is always doing direct sampling for panadapter purposes. If the HDR module is turned off or is not present, the K4 also does direct sampling for demodulation.
If the HDR module is turned on, two additional ADCs are used, right at the outputs of the crystal filters (oversimplifying a bit). The original two ADCs are still being used for the panadapter. Wayne N6KR > On May 29, 2019, at 5:18 PM, Bill Frantz <fra...@pwpconsult.com> wrote: > > Hi Skip. Let me take a stab at some of these, and thanks to Alan, Jeff, and > W2XJ for furthering my technical education about ADCs. > > (1) With direct sampling, if you are operating in a contest, you can keep an > eye on other bands, like 10M in the current conditions, while operating on > bands which have propagation. It's just another window on the screen. A > superhet will severely narrow the bandwidth in the IF stages, so you need a > separate superhet for each band (ala the 2nd receiver in the K3). > > (2) As far as I can tell, the K4HD should perform as well as a K3, or perhaps > even better. Using the formula Alan posted, if I'm tuning a 4KHz FT8 band on > a K4 with its 122 MHz sample rate, I will get a 44.8 dB improvement in S/N > from the over sampling. I would get 47.6 dB for a 2.1 KHz SSB bandwidth and > 60.8 dB for a 100 Hz CW bandwidth. (These are ranges I normally use in my > operations.) Add the 77 to 85 dB range for a real 16 bit ADC with real > support circuitry (these numbers are admittedly a WAG), and you get some > pretty respectable performance. > > You also win big with the K4HD in the same way as with the K3. The IF filters > greatly suppress signals not in the passband, such as that CW station in the > tent next to your RTTY station, (which describes the WVARA QRP field day > setup). > > (3) The details of the K3 ADC are beyond my current level of knowledge, but > the documentation lists it as 24 bits, as does W2XJ's post. > > 73 Bill AE6JV > > On 5/29/19 at 4:01 PM, k6...@foothill.net (Fred Jensen) wrote: > >> I understand what direct sampling is and how it works. Why is it preferable >> [or whatever other positive term you might want to use] to the superhet >> design of the K3(s)? I'm curious what sampling the entire spectrum from 0.1 >> MHz to 54 MHz buys me? >> >> If I understand the "Superhet" option for the K4 correctly [problematical at >> best], it provides RF and mixer stages to an IF [~8 MHz??] which is then >> directly sampled by the base K4. Since that IF bandwidth can be adjusted by >> xtal filters and will be MUCH narrower than 0.1 - 54 MHz it will also be far >> less susceptible to overload from strong signals not in that passband. Is >> this what's going on? >> >> For reasons I cannot remember now, I thought the K3(s) oversampled the 15 >> KHz 2nd IF with a delta-sigma 1-bit ADC and decimated to the equivalent of a >> 22-bit word. Some of the thredlets here have now caused me to reconsider >> that belief. Have I got it wrong? > > ----------------------------------------------------------------------- > Bill Frantz | Privacy is dead, get over | Periwinkle > (408)356-8506 | it. | 16345 Englewood Ave > www.pwpconsult.com | - Scott McNealy | Los Gatos, CA 95032 > > ______________________________________________________________ > 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
