> As for gain pumping and inter-signal IMD: the likelihood that > you are actually going to encounter a situation that requires a > narrow roofing filter for PSK seems quite remote. Extremely > strong PSK signals are not that common, PSK signals turn on and > off only on time scales of several seconds, and PSK detection is > not highly amplitude-sensitive, so both the likelihood and the > effects of gain pumping and inter-signal IMD would appear to be > much reduced compared to other modes.
That's easy to say in theory. However, when your neighbor fires up with his amplifier in a pile-up and activates the HACG you need the 200 Hz filter "bandpass" decoding simply is not going to do the job. 73, ... Joe, W4TV > -----Original Message----- > From: elecraft-boun...@mailman.qth.net > [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Richard Ferch > Sent: Wednesday, December 30, 2009 9:19 AM > To: elecraft@mailman.qth.net > Subject: Re: [Elecraft] [K3] Best Filter for the K3 when > operating PSK31 > > > G4ILO wrote: > > Brandon673 wrote: > >> > >> I would like to hear opinions and reasons for the best > filter to use > >> for operating PSK31 with the K3. > >> > > > > You don't need anything more than the SSB filter. > > I agree with Julian. Remember, it is the DSP that is responsible for > signal filtering. You do not need narrow roofing filters to enable > narrow DSP filtering - you can narrow the DSP filter down to > 50 Hz even > if the only roofing filter you have is 2.7 kHz wide. The job of the > roofing filters is just to keep unwanted strong signals out of the IF > bandpass to prevent gain pumping (desense) and IMD (splatter > generated > in the receiver) caused by those unwanted signals. > > Regarding DSP filter settings: Wide filter settings are > useful to scan > the band, for S&Ping, and for multiple signal decoding. Once you have > picked a signal to work, or if you are calling CQ, narrow DSP filter > settings can be helpful. You can put your DSP filter controls in > SHIFT-WIDTH mode and use the two controls to focus on the desired > frequency, or you can use an Align or Optimize feature in > your software > to center the desired signal at a chosen frequency so you > only need to > adjust the WIDTH control. > > As for gain pumping and inter-signal IMD: the likelihood that you are > actually going to encounter a situation that requires a > narrow roofing > filter for PSK seems quite remote. Extremely strong PSK > signals are not > that common, PSK signals turn on and off only on time scales > of several > seconds, and PSK detection is not highly amplitude-sensitive, so both > the likelihood and the effects of gain pumping and inter-signal IMD > would appear to be much reduced compared to other modes. > > Bottom line: I'd suggest you base your decisions re roofing > filters on > your needs for other modes, not on PSK31. > > 73, > Rich VE3KI > ______________________________________________________________ > 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
