Tom; The K3 has two filter types. The main one is provided by the DSP. It does an outstanding job of cutting down signals outside the bandpass that you don’t want to hear. Learning to use this filter well will give you lots of pleasure with your new K3. The second is the roofing filter, which is what you are asking about. These provide very good filtering for extremely strong signals. These are usually from near-by transmitters with signals so strong that they overload the front end of the receiver. When I was in Silicon Valley I had quite a few of those in the area, so I needed to add a few filters in my K3s; for the most part I don’t need this so much here in Louisiana. The other roofing filters that are of use are the 6 KHz and 13 KHz filters that are needed for AM and FM operation (respectively).
Having super-narrow roofing filters for CW is very argumentative. I find that the DSP handles my needs quite well with the 500 Hz filter. I will, at times, go even wider with the DSP, thus using the 1.7 KHz roofing filter. You do not want a narrow filter for RTTY, it will create problems for the decoder. You actually want pretty wide bandwidth for RTTY, and as wide as you can get for FT8, FT4, and the other PSK modes. My advice, learn to use the DSP filter with the filters you have now, then look at adding other roofing filters if you find that near-by super powerful stations are giving you problems. As for the DSP filters, the best advice - for CW use the center/bandwidth setting, and vary the bandwidth as needed. The only time I vary the center frequency is when I accidentally grab the wrong knob. For SSB, use low cut / high cut. You will probably find that parking low cut somewhere around 300 or 400 Hz will do very well, although sometimes I will drop that setting to zero to help with some stations. High cut will vary, in heavy traffic conditions (contests, chasing DX), you may drop it as low as 1600 to 1800 Hz. I normally leave mine in the range of 2100 to 2500 Hz, widening it for high-pitched voices (usually female, or N3QE’s Tina). Using your K3 will tell you what you might want in the way of roofing filters. If you have the SubReceiver, you will want to consider filters for that receiver as well. The SubReceiver has many uses, including diversity reception, which can be really helpful on the low bands. Both of my K3s have them, and they are rarely used these days. I use both transceivers simultaneously (SO2R), and have a difficult time listening to four receiver streams simultaneously. 73! Jack, W6FB > On Dec 24, 2025, at 10:43 AM, Tom Bowles via Elecraft > <[email protected]> wrote: > > Hello all, > > I recently acquired a K3 that came with the standard 2.7 kHz and a 500 Hz > roofing filters installed (no subrx). I mostly operate CW, SSB, and sometimes > RTTY contests, and I'd like to round out my filter set for better performance > in crowded bands. > > I'm considering adding a 1.8 kHz for SSB and a 250 Hz for CW, but I've read > that the 250 Hz filter often measures wider in practice (around 330-350 Hz) > and may not be as sharp as expected. Has anyone experienced this, and would > you recommend it, or suggest alternatives like the 200 Hz or 400 Hz instead? > > 73, > Tom KE5CW > ______________________________________________________________ > 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]
