How does the below compare to the K2? There are no roofing filters in the K2, right?
In my homebrew receivers, I have a high Q tuned circuit at the antenna, then into the mixer, the output of the mixer goes to my filters (KIWA), then the IF chain. There is nothing to roof there, right? I get artifacts of close signals, but not from the receiver, from the transmitter... The $50.00 KIWA filters are good enough so if its out of the passband, its not there. Now I wonder why you cant just go from the mixer into the DSP... Brett N2DTS > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of DOUGLAS ZWIEBEL > Sent: Tuesday, May 01, 2007 7:59 PM > To: [email protected] > Subject: [Elecraft] roofing filters - when to use them > > Hi all: > > Well, Bill (ZV) gave a nice (brief) summary and pointed to a nice > reference. Ten Tec had (maybe it is still there) some good info also, > but specific to their radio...however, you can still use it to get a > "feel" for a what a roofing is (and what it isn't). If you're a > member of ARRL, go to their web page and search on Roofing Filter. > > Don (FPR) cited some uses which I am not familiar with (data), so no > comment from me on that. > > I've commented directly to the source about my "wonder" at why one > would want a variable roofing filter. As Lee said, one "wide" and one > "narrow" is enough (at least for SSB / CW only operation). > > If I'm on CW and my radio is hearing squeaks, pops, and "garbage" due > to lots of LOUD signals being in my passband (say 15 or 20kc wide on > an "old" radio), I would not be able to do much...maybe cut back on > the RF gain, add some attenuation, etc. However, if I could narrow > the passband (the roof) to say 1kc, the likelihood of two (or more) > very loud signals being captured within that 1kc is greatly reduced. > If I use a 500hz roofing filter (assuming all other parameters could > remain unchanged), the odds of having two (or more) "other" very > strong signals there (besides the one I want to copy) is even > less...hence less chance of squeaks and pops masking the signal I want > to copy. BTW, the squeaks and pops = IMD Products. > > Of course, if there were that many LOUD signals that close together, > I'd simply move (qsy) to a clearer (relatively) spot. > > Why in the world one would want to take the time to "carefully" or > "slowly" adjust a roofing filter's bandwidth is beyond me. I would > simply dump in my "narrow" roofing filter and be done with it. Either > it works or it doesn't; why play around? > > This topic is of major concern to contesters, especially (mostly) on > the low bands. I know...it is also of concern to Europeans on 40m > even NOT during a contest...true. > > If you're not a SERIOUS contester or Low Band DXer (or data guy ala > Don's description?), I have a hard time understanding why you'd want > these "narrow" filters. Hey look, 2.7kc is pretty darn narrow > compared to most of what is out there. Again (as had already been > cited), even the IC7800 and FT9000 have a 3kc roofing filter as their > narrowest (which I don't think is good enough for some CW situation). > > I would guess that for 95% of non-serious contesters, or non-low band > DXer (and digital guys?), you'll be VERY happy with a single 2.7kc > roofing filter for SSB and even for CW. For those who are used to IF > filters, this is just not the same. You'll still have that with the > K3....twiddle the bandwidth any way you like (narrow). Remember, > roofing filters are for CROWDED band condx FILLED with LOUD signals > (with the digital proviso still there). > > And NOW, I'd like to say, I have no idea exactly how much MAGIC the > Aptos boyz have included in this radio and for all I know (not having > the radio, the specs, schematic, code, etc., they may have come up > with something that voids all of the above. Wouldn't that be great! > > de Doug KR2Q > _______________________________________________ > Elecraft mailing list > Post to: [email protected] > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com > _______________________________________________ Elecraft mailing list Post to: [email protected] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
