This sounds like a fun area to study, Thanks for putting me on the path. I will look up KK7B's work.
KV4TT - Mike On Fri, Dec 22, 2017 at 12:37 PM, Don Wilhelm <donw...@embarqmail.com> wrote: > Mike, > > Think of the 8kHz shift similar to a low frequency (8kHz) IF if your > thinking is along the lines of a superhet receiver. > > Of course, the KX2 is *not* a superhet, it is a full SDR. If the "IF" > were at a higher frequency, the VFO would be further away from the signal > frequency - by the frequency of the IF. > > The SDR DSP processing is at 8kHz in the KX2, or selectable between > baseband (zero frequency) and 8kHz in the KX3. > > Using baseband has some advantages (the roofing filters), but also some > downsides such as increased exposure to strong radio broadcast signals > leaking into the baseband stream. If you have ever experimented with > Direct Conversion receivers, you will know about that breakthrough. > > An SDR in simplified form is two identical Direct Conversion receivers > operated 90 degrees out of phase with each other. That allows the signal > processing to be done mathematically (whether that be analog or digital). > A study into the Phasing Receivers of Rick Campbell KK7B design along with > op-amp mathematics will give you the analog version of that signal > processing. > The problem with analog implementation is that real components have > tolerances that must be dealt with - digital mathematics can be exact > calculations. > > 73, > Don W3FPR > > > On 12/22/2017 12:07 PM, Michael Zabel wrote: > >> Hi Don, >> >> Thank you for the great explanation. >> >> I must have had the ATT on when I did the original power measurement >> (rough) on the SDR >> >> I tested again and this time I get: >> >> -77dBm - Preamp On >> -55dBm - Preamp Off >> -74dBm - ATT on >> >> Just relative differences with the absolutes unique to my setup of course. >> >> The VFO signal is in the noise with the antenna disconnected from both KX2 >> and SDR. >> The VFO signal is lower when using separate antennas for each as would be >> expected. >> >> I was just not used to seeing a signal like that when using the SDR to >> track superhet's before, so it had me scratching my head for a bit until I >> considered the Rx architecture of the KX2(3). >> >> Thank you for helping me get everything organized in my thinking, >> sometimes >> that is a monumental task! >> > ______________________________________________________________ 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
