I would take issue with your answer to #1. It really depends on your situation. For most of the folks on this list your answer very well may be correct. In areas where there is very high station density, it probably is not. Here in Silicon Valley there are a LOT of very strong near-by signals. The 1.8 KHz filter keeps close-in LOUD signals out of my passband so that the DSP filters have a chance to do their job. This is the whole purpose of the filter, to keep other strong signals out of the passband so that the DSP can do the real work.
By the way, for contesting (actually my main operating mode), I normally listen to SSB signals with low cut at 500 and high cut in the 1500-1800 range, well inside the 1.8KHz filter’s purview. Interestingly, I use matched 500 Hz 5-pole filters for CW contesting, where I can get within just a few hundred hertz of the local big signals without problem. My normal DSP bandwidth is something less that 500 Hz. It’s sideband contesting where I need the narrow filters. Since most of the local big guns also use K3s, phase noise and other similar problems are not a factor here. I really can get close to these folks and work lots of stations without either one of us being disturbed. I credit all this to the great RF system my friends have created. When I’m not in one of the big contests, or just casual QSOs where the big guns aren’t a factor, the 2.7 KHz filter does an outstanding job on whatever mode I use. I guess there is an exception to everything, and indeed there are times when the narrow filters are needed. Some of us actually do fall in that category. Oh to live back in the south where I definitely didn't have the problem… Jack B, W6FB (ex-WA4FIB) On May 11, 2014, at 2:03 PM, Al Lorona <alor...@sbcglobal.net> wrote: > What determines the bandwidth you hear at the loudspeaker? It's not your > roofing filter, despite a continuing notion that it is. > > Dave Hachadorian's point in a post a few weeks ago was that you don't need a > 1.8 kHz filter to get a 1.8 kHz bandwidth. You're free to set whatever > bandwidth you want with any filter. > > Before rigs had DSP we got used to the idea that your crystal filter sets > your bandwidth. That's not true any more. It sets your *maximum* bandwidth. > You then have the freedom to narrow and position a bandwidth arbitrarily > using the DSP controls [SHIFT and WIDTH or HI and LO]. > > > Here's a true-false quiz: > > > 1. I'm a contester, so I need a 1.8 kHz roofing filter in the K3. > > 2. I should purchase the 400 Hz filter if I like to operate CW with > bandwidths of 300 - 400 Hz. > > 3. For SSB, the 2.7 and 2.8 kHz filters are 'too wide'. > > 4. I have the 2.7 kHz filter installed, so for best results I should set my > WIDTH control for a passband of 2.7 kHz. > > 5. I can use my 2.7 kHz filter in CW mode with my LO=0.30 and HI=0.50 (that > is, BW=0.20). > > > The answers are: > > 1. False. You do not need a 1.8 kHz filter just to set the BW=1.80. A 2.7 kHz > filter can serve well during a contest with a much narrower DSP bandwidth. > Refer to Dave's original post. > 2. False. You can set the CW bandwidth to 400 using any filter whose > bandwidth is equal to or greater than 400. > 3. False. This was Dave's point. You're free to have a 2.7 or 2.8 installed, > yet set the WIDTH to 1.8, 1.5 or anything else you wish. > 4. False. You don't need to restrict yourself to only that bandwidth. You can > set it to a narrower value if you wish. > 5. True. And you'll probably suffer no ill effects under most conditions. > > Furthermore, the "but extremely strong signals will pump my hardware AGC" > arguments are probably a bit overrated. Most folks, even before a strong > station gets close enough to do that, will give up and leave the frequency > because of the QRM, especially in the presence of transmitted phase noise or > key clicks as has come up in more recent posts. > > So then why have narrow roofing filters to choose from? To maximize the > close-in dynamic range, which is important if you have large antennas in > high-RF environments. > > The vast majority of hams does not absolutely need really narrow roofing > filters. It's wonderful that the K3 allows this, but it's certainly not > mandatory, especially for casual operating. > > Finally, note that if you received good training as a Novice with a poor, > unselective receiver, you'll be able to copy right through any AGC pumping! > It's the operator, more than the filters. > > > Al W6LX > ______________________________________________________________ > 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 jackbrin...@me.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
