Fred,
Everything you say is true, the DSP does set the final filter width, but
the hardware AGC can cause pumping in the presence of nearby strong signals.
Since my normal desired CW tuning width is in the vicinity of 700 Hz, I
bought and installed one of the 700 Hz filters. YMMV some say that a
1000 kHz roofer is fine, and others say that the 2.7 kHz filter works
just fine too, but I am satisfied with the 700 Hz width - that is a
personal preference, I am not here to convince others about my choices,
but only to give information that will allow others to make intelligent
choices that suit their needs and desires.
73,
Don W3FPR
On 3/1/2014 7:59 PM, Fred Jensen wrote:
If you can, help me out here Don ...
These are roofing filters. From my perspective, which is likely
wrong, their job is to restrict the bandwidth presented to the 2nd
mixer [and downstream ADC]. They are of most value when you have very
strong [i.e. geographically close] signals adjacent to the desired
signal [That would be WX6V for me :-)]. The ultimate BW is set by the
DSP of course, but a really strong adjacent signal can begin to
activate the HW AGC in the K3 which affects the signal inside your DSP
BW, or I think that's true. So, it follows to me that, if you are
plagued by KW neighbors, narrower roofing filters can reduce that
problem. This could be true on FD or any other closely spaced HF
operations ... IF you have two stations on the same band/mode.
If you are not so plagued, I can't figure out why it really matters.
I have the filter that came with the K3 and I bought one [2.7 and .5,
I don't remember which was which], I've had no difficulties. Jim
[WX6V] and Jack KF6T [equally close] became non-problems when I got my
K3 ... even more so now that Jim has a K3 and phase-noise has
disappeared. :-)
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