I've received emails replies (direct and otherwise) that, for me, indicate that I should elaborate/clarify what I am referring to.
Let's assume that you have a 2.7 and 2.1 roofing filter. If you set up your "narrower" SSB filter according the the manual, which is what the majority of K3 ops do, as you transition from, 2.7 to 2.1 using the width "knob," you are doing two separate, but linked things. First, you are reducing the DSP BW. Sync'ed to that (you have no choice without manual intervention, ie "faking out" the K3), as you get to 2.1 kHz in the DSP BW, you simultaneously switch from the 2.7 to the 2.1 roofing filter. Unless you "unhook" this coupling between the DSP BW and the Roofing Filter BW, you simply cannot "tell" which one is influencing what you hear (what I called "feel"). So when you get down to 2.1 (from 2.7) are you appreciating the impact of the DSP or the roofing filter - or maybe both? How would you know? I am saying that unless you are operating in extremely crowded band conditions (not with just one "interfering, very near-by station") you are appreciating the impact due to the DSP BW and certainly NOT the roofing filter. It is possible to manually intervene to alter (even temporarily "turn off") the (point of) sync between the DSP BW and the roofing filter (narrower) BW. And I am saying that unless you actually do this "de-linking," that you won't be able to know/confirm the true source of what you are hearing / feeling. I'm betting that for the vast majority, especially non-contesters and non-160 serious DXers, what you hear is due to the DSP BW. The roofing filters are used for reducing IMD. A receiver with poor IMD will experience "phantom signals" due to the mixing of other very strong signals (multiple) on the band and these phantom signals can potentially cover up real, but weak, signals. You can usually identify such IMD as received "squeaks, pops, whines, groans, etc." The band will sound like it is covered with garbage - even somewhat "musical. The addition of the appropriate roofing filter can reduce or eliminate this. This is esp true (for me) on CW and especially (for me) on the low bands (lots of very strong signals) during a contest. In "the old days," I've had many receivers that would simply collapse under the strain. It made tuning across the band painful and arduous when trying to pick out weaker signals. After hours and hours of this, it is very fatiguing. I use the 5 pole 500hz filter on CW for both of my K3s. Is it "wrong" to get a narrow filter? Of course not. But unless you are planning on operating in the midst of multiple, super strong signals, then I do not see much "logic" in getting a narrower CW filter...and certainly not a narrower SSB filter for SSB use. At least on CW, you can fit another signal inside the passband (very rare) when going from 500 to 200hz, but on SSB, going from 2.7 to 2.1? No way that will "fit another signal" in that delta (which is half of the difference or just 300hz.). Now, if you have the sub-receiver and want to "match" filters, then I see nothing wrong with buying one of the narrower (or even wider) SSB filters. But that would be motivated by a different reason. If you're spending money frugally or even just "being thrifty," (however you want to define that) you can stick with the 2.7 stock filter. If money isn't an issue (the cost isn't that much different), you sure can't be "hurt" by getting a narrower SSB filter, except as cited by others, when it comes to "ease" of tuning in a station (though I have never experienced such difficulty). Lots of folks simply like to "load up" the open the slots. That is yet another motivation...not much to do with operating. Hope this helped to clarify what I was trying to get across. de Doug ______________________________________________________________ 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
