roofing filters - when to use them
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roofing filters - when to use them
 
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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: [hidden email] 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 |
RE: roofing filters - when to use them
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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: [hidden email] > [mailto:[hidden email]] On Behalf Of DOUGLAS ZWIEBEL > Sent: Tuesday, May 01, 2007 7:59 PM > To: [hidden email] > 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: [hidden email] > 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: [hidden email] 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 |
Re: roofing filters - when to use them
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Brett,
While there are DSP processors that *CAN* operate at higher frequencies (like the receiver 1st IF), they are very expensive - the downconversion to the DSP IF at 15 kHz is a much more economical approach. If you want to look at it that way, the filters in the K2 act both as a roofing filter and a final selectivity filter - but in that context, the term 'roofing filter' is a misnomer. 73, Don W3FPR Brett gazdzinski wrote: > 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: [hidden email] >> [mailto:[hidden email]] On Behalf Of DOUGLAS ZWIEBEL >> Sent: Tuesday, May 01, 2007 7:59 PM >> To: [hidden email] >> 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: [hidden email] >> 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: [hidden email] > 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: [hidden email] 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 |
Re: roofing filters - when to use them
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In reply to this post by DOUGLAS ZWIEBEL
Hi Doug, I wanted to relate to your assessment of "narrow" filters.
When I was first introduced to Ham Radio I was very fortunate to meet Harry W9TT. Harry was a super-duper NTS operator and net control. He *INSISTED* that I keep his old BC-??? set to the WIDEST setting for his CW nets. The obvious reason was that in 1960 many of the 80M crystals we ground ourselves were in the "ball park" but not dead zero beat on the NCS. If he sent two guys down 2 or 3k to pass traffic, he wanted to hear them in the peripheral vision in his head. That way he "knew" when they were through passing their traffic and he would anticipate their return or sending someone else down to meet them. He taught me to simply listen to one station of interest and let the others carry on. I have never understood the obsession of the modern CW ops with *narrow* filters. I use my brain and don't seem to miss any QSOs ;-) TU for reading, 72/73 de Ken N9VV (K9DNY 1960) DOUGLAS ZWIEBEL wrote: > 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: [hidden email] > 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: [hidden email] 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 |
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