Thanks for the reply Guy.
I understand your rationale for aligning IF and DSP filters for additional out-of-passband rejection in crowded contest conditions. My concern stems from using IF shift to move the DSP filter within the roofing filter passband. The Elecraft rep I spoke to last week told me that the 8 Mhz IF roofing filter and the DSP filters do not track. The roofing filter is fixed and will present a fixed bandwidth in which the DSP filter can operate. Therefore, there will be an interaction between the two filters, the fixed roofing filter, and the DSP filter which can be moved higher or lower with the IF Shift control. If the roofing filter and the DSP filter have the same bandwidth, the interaction between the filter skirts creates a high cut or low cut condition depending upon the direction of the IF shift. If the IF can be shifted enough, a stop-band condition occurs and all signals disappear. I am primarily a "search and pounce" contester, but I can appreciate your desire to have the sharpest combined filter skirts to keep the adjacent run station from getting into your bandpass. However, my limited experience with "run" contesting revealed that extremely sharp filters are a double-edged sword because of the inability to hear off-frequency callers. In fact, I think there is an option in the K3S menu system that provides for higher shape factor DSP filters in order to allow off-frequency caller to be heard. In the S&P contest mode, I also want very sharp DSP filters, but I want them to exist within a wider roofing filter bandwidth so that I can use the IF shift to discriminate between signals in that passband. If my DSP filter and my roofing filter are about the same bandwidth, I can't use the IF shift effectively because its filter skirts will interact with the roofing filter skirts and cause an undesirable high cut or low cut resultant filter response, or worse, the dreaded stop-band condition. Another consequence of cascading a roofing filter and a DSP filter of the same bandwidth in a run contest mode is that the only recourse to hear an off-frequency caller is to engage the RIT (since engaging IF shift with result in the above stated undesirable resultant filter response curves). When I am in "run" contest mode, especially in very crowded conditions, using RIT changes the pitch of every station that is audible, and I just don't like to lose my awareness of where each station is. I much prefer to use the IF shift to "highlight" the caller I want to contact without changing the pitch of every single station. Therefore, I hope you can see why I would not want to have a roofing filter that is too narrow for the DSP filter that I plan two use in combination with IF shift. Since I like to use the 100 hz DSP filter bandwidth, I would not chose the 200hz roofing filter as an option because it would severely limit the amount of IF shift that I could use with a 100hz DSP filter. If I were not a fan of IF shift, I would do what you are doing, cascade the 200hz roofing filter and use the 100 or 200 hz DSP filter. In summary, I am hoping that the DSP filters have very steep skirts to maximize the IF shift that can be used before the DSP filter skirts interact with the roofing filter skirts. If you have any data on the narrow DSP filter plots, please let me know. Charles K5UA ______________________________________________________________ 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
