As usual, Fred has things pretty much right. Here in Silicon Valley narrow roofing filters are needed to keep the local massive signals out of the receiver. With the 500 Hz 5-pole filter I can operate within a few hundred hertz of the big guys with very little problems. In fact it is pretty cool in Sweepstakes to be running with local 1500 watt stations up and down just a few hundred hundred hertz, not affecting my receiver at all. The DSP will be set to about 200 Hz in this situation. Without the local high-power stations, I like to widen out the bandwidth as much as possible so I can hear stations calling me that are away from my frequency, just like we used to do it in the days of the SB303, KWM2, etc.
Now on voice it is a different matter. 500 Hz doesn’t cut it. I use an 1800Hz filter there, and set the DSP for 500 Hz low cut and something around 1500-1800 Hz high cut. Sometimes it helps to drop the low cut a bit for someone with a deep voice, or raise the high cut for an YL. And again, under light conditions, I’ll widen up the filter to make use to the 2.7KHz roofing filter. The roofing filters just keep big signals lout, allowing the DSP to do the really great job Lyle designed it to do. Jack B, W6FB On Mar 1, 2014, at 4:59 PM, Fred Jensen <k6...@foothill.net> wrote: > If you can, help me out here Don ... > > These are roofing filters. From my perspective, which is likely wrong, their > job is to restrict the bandwidth presented to the 2nd mixer [and downstream > ADC]. They are of most value when you have very strong [i.e. geographically > close] signals adjacent to the desired signal [That would be WX6V for me > :-)]. The ultimate BW is set by the DSP of course, but a really strong > adjacent signal can begin to activate the HW AGC in the K3 which affects the > signal inside your DSP BW, or I think that's true. So, it follows to me that, > if you are plagued by KW neighbors, narrower roofing filters can reduce that > problem. This could be true on FD or any other closely spaced HF operations > ... IF you have two stations on the same band/mode. > > If you are not so plagued, I can't figure out why it really matters. I have > the filter that came with the K3 and I bought one [2.7 and .5, I don't > remember which was which], I've had no difficulties. Jim [WX6V] and Jack > KF6T [equally close] became non-problems when I got my K3 ... even more so > now that Jim has a K3 and phase-noise has disappeared. :-) > > I've got to be missing something here, and sadly, it wouldn't be even close > to the first time. > > 73, > > Fred K6DGW > - Northern California Contest Club > - CU in the 2014 Cal QSO Party 4-5 Oct 2014 > - www.cqp.org > > > On 3/1/2014 4:03 PM, Don Wilhelm wrote: >> Eric has permitted such announcements, but limits them to one a month. >> You will see offers to build a K2 that come in that same category. >> >> Personal comment -- I particularly like the 700 Hz CW filter in my K3. I >> got used to tuning the bands using a 700 Hz filter width in my K2, and >> opted for the 700 Hz roofing filter when it was offered. Yes, I find it >> nice for 'scouring the pileup' before switching to the narrower 400 Hz >> filter when listening to a pileup. YMMV, but it is an available option. > > > ______________________________________________________________ > 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 ______________________________________________________________ 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
