Exactly right, Will. In the K3/K3S, we have a very strong mixer and post amp followed by crystal filters at the first I.F., 8.215 MHz. Since the IF and ADC are down-stream from these filters, they are very well protected from out-of-band signals.
Our crystal filters are manufactured to very tight tolerances and as a result, provide consistently high dynamic range. The P3 panadapter gets its signal ahead of the crystal filters so it can display a wide spectrum. It is in effect a direct-sampling SDR in its own right. The beauty of having the panadapter’s receiver chain (P3) fully separate from the demodulation receive chain (K3) is that demodulation remains unaffected (up to very signal levels) even if the panadapter has to separately reduce its own gain. “Pure” SDRs (IC7300, IC7610, Flex) don’t have this luxury; everything runs from the same wideband ADC, without narrowband protection via crystal filters. Another K3/K3S advantage is in its very narrow ham-band RF filters. These are positioned ahead of the P3 pickoff point, benefitting both the panadapter and demodulation channels. 73, Wayne N6KR > On Jun 13, 2018, at 11:38 AM, WILLIE BABER <wlba...@bellsouth.net> wrote: > > Robert is talking about the crystal filters, also known as roofing filters > now-days, that are typically placed after the first mixer (I mistakenly typed > "ahead" but I meant "after" as Robert notes), though there is a post amp and > NB before these filters in K2 and K3. > > The idea is that a crystal filter right after the first mixer gives high > dynamic range because high selectivity comes before the receiver has > developed stages of gain that otherwise could cause blocking or IMD, > especially when selectivity is postponed to the second mixer while ignoring > gain distribution in prior stages of the receiver. This basic idea was > popularized in Solid State Design for the Radio Amateur, and it was applied > to Ten-Tec radios for decades (at a 9 mhz I-F). > > Roofing filter gets defined in relationship to Japanese radios that had up > conversion 15 khz filters at the first I-F, and generally lower dynamic range > as a result, (but you got all modes, general coverage, and optional crystal > filters at the second I-F). > > Good for everyone radios.... but with lower dynamic range and phase noise > from the early synthesizers. This is why Ten-Tec radios were so popular > among contesters, especially Omni V and VI (modified with a narrow cw filter > at the first I-F). > > 73, Will, wj9b > > > > CWops #1085 > CWA Advisor levels II and III > http://cwops.org/ > > -------------------------------------------- > On Wed, 6/13/18, Jim Brown <j...@audiosystemsgroup.com> wrote: > > Subject: Re: [Elecraft] Field Day rig experience > To: elecraft@mailman.qth.net > Date: Wednesday, June 13, 2018, 10:36 AM > > On 6/12/2018 4:50 PM, Robert G > Strickland wrote: >> A small nit... > perhaps my ignorance... but, I think that the roofing >> filter [by whatever name] comes after the > first mixer, at the >> so-called IF > frequency. > > A month or so > ago, as part of a project to measure input Z of receivers > > and preamps, I measured the 2nd RX of my K3 > as 50 ohms and with a > bandpass filter > between the antenna input and the 50 ohm load. Clearly, > in the K3, there is a "per band" > bandpass filter ahead of the first RF > stage. > > 73, Jim > K9YC > > ______________________________________________________________ > 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 wlba...@bellsouth.net > > ______________________________________________________________ > 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 n...@elecraft.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
