Wes, "A "Roofing filter" is simply a filter in the radio's first IF through which all signals must pass before they will be "seen" by later receiver stages. The narrower this filter is, the less exposure later stages will have. Thus a "narrow" roofing filter is desirable -- but "narrow" is relative, as I'll explain."
What Elecraft said (above) is exactly what I said. Moreover, Elecraft's explanation is required because the term roofing filter is now applied to up-conversion in multiple conversion radios (with relatively wide first I-F filters compared to what is achievable at a low first I-F) which is what the term initially sought to rebuff in the first place, also my point. 73, Will, wj9b CWops #1085 CWA Advisor levels II and III http://cwops.org/ -------------------------------------------- On Thu, 6/14/18, Wes Stewart <wes_n...@triconet.org> wrote: Subject: Re: [Elecraft] Field Day rig experience To: elecraft@mailman.qth.net Date: Thursday, June 14, 2018, 4:47 PM Will, First of all I have said before and will repeat it, I detest the term "roofing filter." That said, by the generally accepted definition, you are wrong. See Elecraft's take on this: http://www.elecraft.com/K3/Roofing_Filters.htm If you will think in Wayne's terms, the post-mixer filter is a "protective" filter, not a mode-specific filter. So the question becomes, how much protection is necessary? In Elecraft's case, quite a lot, IMHO. With its QRP DNA, Elecraft uses post crystal filter circuitry that minimizes current consumption. The trade off for this is the need for a bank of pricey crystal filters to limit the frequencies that the circuitry is exposed to. Now what if the subsequent circuitry doesn't require this much protection because it is more robust? We now have direct-sampling radios that can digitize a whole ham band with good performance. If the BW was limited to 10-15 kHz in an up conversion configuration they should be even better. The limitation now becomes LO phase noise, but newer synthesizer designs overcome that obstacle. Another thing to note is that IMD in crystal filters is reported to be inversely proportional to BW. So a wider filter might actually be better from that perspective. Some Elecraft filters exhibit passive IMD BTW. Wes N7WS On 6/14/2018 8:01 AM, WILLIE BABER wrote: > Hello Wes, > > I took a look. Both designs are using the idea of "roofing filter" to refer to up-conversion radios similar to the use of up-conversion 3khz filters as roofing filters in Icom radios. > > "Roofing filter" (a mode specific filter after the first mixer including narrow cw filters) only makes sense in the context of the history of superhet design and in particular the use of one broad 15 khz first I-F (so that all modes may pass through it) typical of all Japanese radios until recently. Calling a 45 mhz filter at the first I-F a "roofing filter" as noted in the info you sent entirely misses the point of what roofing filter means. Or, to put it another way, all Ten-Tec radios had roofing filters in them (and were ssb and cw only) well before the term roofing filter was coined! Which is why an Omni C will out perform any wide (15 khz) first I-F Japanese radio, even those built well after the 1980 vintage Omni C. > > Unless mode specific up-conversion crystal filters can be made and as narrow as 200 hz (this is possible with down-conversion) then "roofing filter" and up conversion doesn't make sense historically or in reality. > > Actually, Icom says that did it with 1.2khz filter at 64 mhz in the Icom 7851, though I'm not convinced the filter is that narrow, and 1.2khz is far from the 200hz filter that my K3 has in it (however, the placement of this filter is why the 7851 is among the best radios in Sherwood's chart, on cw). > > It is possible to make very narrow and precise crystal filters as narrow as the 200 hz inexpensively, and this is the point of having multiple roofing filters at the first I-F. So, this is the origin of the term roofing filter---in comparison to the barn-door up conversion first I-F. > > 73, Will, wj9b > > CWops #1085 > CWA Advisor levels II and III > http://cwops.org/ > > -------------------------------------------- > On Wed, 6/13/18, Wes Stewart<wes_n...@triconet.org> wrote: > > Subject: Re: [Elecraft] Field Day rig experience > To:elecraft@mailman.qth.net > Date: Wednesday, June 13, 2018, 3:08 PM > > Certainly not to disparage the > K3(S) architecture (I have two of them) there is > nothing inherently wrong with an up-conversion > receiver, if modern hardware is used. > > See:https://martein.home.xs4all.nl/pa3ake/hmode/g3sbi_intro.html > > and my friend Cornell's, > Star-10 transceiver. > >https://pdfs.semanticscholar.org/eb33/5c12858779a653d9b9b93ca20120aebb7616.pdf > > Wes N7WS > > > On 6/13/2018 11:38 AM, WILLIE BABER > 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 > > > > ______________________________________________________________ > 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 towlba...@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 towes_n...@triconet.org ______________________________________________________________ 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 arch...@mail-archive.com
