[Elecraft] K3 - Filter suggestions for new builder

[Al Lorona]

Another way of looking at it is this:

Just because a signal gets inside of your roofing filter doesn't mean squat. If 
the mixers can handle the signal's level, and the HI LO cut controls can slice 
off the signal, you won't even know it's there. You simply don't care!

The only time this could become a problem is if the signal that squeezes into 
your roofing filter is huge. Then it could start polluting your passband with 
intermod products or activating your AGC. EVEN THEN, most hams can't even detect 
the first 10 dB or so of this distortion. And it's such a rare event: operating 
a really hot contest with a really big antenna with just the right combination 
of interferers; or your ham neighbor very close to you, etc. In these corner 
cases, you can justify extreme measures of narrow roofing filters, etc. 

I believe that 99% of us can get by with 1 SSB roofing filter and perhaps 1 
CW-width roofing filter. The intermediate bandwidths are really overkill. So 
don't sweat a 2.7 vs. 2.8 kHz filter so much. You can't tell the difference when 
you're listening to an SSB signal with the HI LO controls set to a WIDTH of 2.4 
or 2.6 kHz.

Agonizing over buying a roofing filter of 2.7 or 2.1 kHz is a little like 
worrying if you should go for the 89 octane gasoline. If you've got the money, 
go for it. But you probably won't notice any difference at all.

Finally, I will say this: if you find your 1.0 kHz roofing filter isn't wide 
enough to protect you against, you know, W4ZV's super contest signal, you're 
probably too close to him. In that case, just move about 600 Hz up the band. :^)

With the utmost respect to W4ZV,

Al  W6LX