I think what they are seeing is this: Strong signals that fall slightly outside the DSP's audio passband are still pumping the S-meter and the AGC is desensing the receiver. The DSP is acting more like and audio filter than an IF DSP. In other words, the DSP's audio bandpass is very steep but it's IF bandpass is broad. This is with the 200Hz roofing filter installed but we are dealing with this 50Hz issue. To illustrate, tune in an S-9 carrier using the 50Hz filter. Tune off his signal 60Hz. The audio is gone but the S meter still reads S-9 telling me that the slopes for audio and IF are different. Also, at 50Hz BW the Passband tuning is indeed useless since it tunes in 50Hz increments. Can that be reduced? Steve Ellington n...@carolina.rr.com ----- Original Message ----- From: "wayne burdick" <n...@elecraft.com> To: "K2MK" <k...@comcast.net> Cc: "Elecraft Reflector" <elecraft@mailman.qth.net> Sent: Sunday, February 22, 2009 9:27 PM Subject: Re: [Elecraft] K3 receiver desensing on CW during contest
> Mike, > > The K3 is virtually desense-proof, with a BDR of ~140 dB. But to take > advantage of this, you need a narrow crystal filter -- the closer to > the DSP bandwidth the better. This is exactly the situation that we had > in mind when we designed the 200-Hz 5-pole filter. For CW pileups, you > can't beat it. > > What crystal filter were you using at the time? > > Of course if the transmitting stations are "wide" due to key clicks, > there may be situations where no amount of filtering can help (for any > receiver). The DSP noise blanker and NR may be useful sometimes -- you > might give this a try. > > Wayne > N6KR > > On Feb 22, 2009, at 4:45 PM, K2MK wrote: > >> I had a great time with my K3 during the ARRL DX contest. I do S&P and >> I was >> trolling around with my filter width at 50Hz. Absolutely outstanding. >> The >> auto spot is equally outstanding. >> >> At 50Hz width it was quite clear that many stations call off frequency. >> Using RIT, I could see that it was typical for them to be 70Hz or more >> away >> from the DX station but I could not hear them in my 50Hz passband. The >> real >> problem was when one of them was S9 or greater. They completely swamped >> weaker DX stations. > > --- > > http://www.elecraft.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 > ______________________________________________________________ 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
