2.7 can be used in all modes but FM (not wide enough). As you narrow the bandwidth control, the filters will switch (if in place and enabled). (Also from memory, now using K4s).
To answer the OP, I suppose someone might want to hear a 2.7 KHz wide CW spectrum but that’s a lot of abuse to the ears; 500 (even in a contest) would make more sense. If other narrower filters were installed, I wouldn’t use 2.7 on CW. (250, is really about 325, it’s not that sharp. Most found it not worth the expense.) 73, Rick nk7i > On Dec 6, 2025, at 11:21 AM, Rich Newbould via Elecraft > <[email protected]> wrote: > > If memory serves my correctly the 2.7 filter is used for TX on all modes, > except AM > > I could be wrong > > Rich > > >> On 12/6/2025 1:35 PM, Tony Casciato via Elecraft wrote: >> Was poking around in the K3 Utility this morning and noticed in the >> Configuration tab/Crystal Filter Configuration panel there are Radio Button >> choices for a TX CW filter to use Filters 1 thru 5; mine defaults to Filter >> 3 which is the 2.7Khz 5-pole standard one. I also have Filter 4 (500Hz >> 5-pole) and Filter 5 (250Hz 8-pole) available. Should it be set to >> something different for CW? >> >> I looked in the "Help" text, asked Google and didn't see an option to >> search these Mailman messages. I figured it was ok to ask here once and >> it's mostly a curiosity. >> >> Thanks and 73, >> Tony, KX3H >> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[email protected] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> Message delivered to [email protected] > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [email protected] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
