[Elecraft] K3 XFIL Button

[Don Wilhelm]

Ed,

Keep in mind that the DSP provides the ultimate filter width, the one 
situation you asked about - roofing filter wider than the DSP filter is 
already present - just set the filter configuration to "lie" about the 
actual filter width, and the roofing filter will be switched in at a DSP 
width that is wider than the roofing filter.

The other (DSP filter wider than the roofing filter) does not make much 
sense to me.  Yes, in the filter configuration, you can tell the K3 that 
the (for example) 400Hz filter is really a 600 Hz filter, then you have 
accomplished what you desire.

I do not have much use for the XFIL button and never use it. I let the 
Width control (or HiCut/LoCUT for SSB) switch in whichever roofing 
filter is appropriate and consistent with the DSP width I have selected 
and it works well.

The DSP filter width is a "brick wall filter" and you will not be able 
to hear signals outside that bandwidth.

Keep in mind the purpose of the roofing filters.  In a crowded band, the 
roofing filters keep strong adjacent stations from activating the 
Hardware AGC which is there to protect the ADC from overloading.  In 
other words (again using the 400Hz roofing filter example), if you have 
the DSP bandwidth set at 300Hz centered on [150Hz plus sidetone pitch = 
750 Hz], and you have a very strong signal at 850 Hz, you will not hear 
the strong signal because of the DSP width, but it will activate the 
hardware AGC causing the AGC to 'pump' and the receiver sensitivity will 
be reduced as a result of that 'pumping' - even though you cannot hear 
the signal.

As an alternative, you might want to try turning on DUAL PB in the menu 
which will give you a wider passband that is attenuated from the narrow 
filter peak (or focus).  I believe that will give you what you seek.

73,
Don W3FPR


On 2/20/2019 5:15 PM, Ed G wrote:
> Seems like the K3 XFIL button essentially does the same thing as the DSP width knob. That is, depending on how the user has set up the filter configuration, both DSP and filter selected are pretty much automatic and linked together. Adjusting the width knob will result in a particular crystal filter being selected, and similarly, using the XFIL button to select a filter will automatically adjust the DSP setting.
> 
> On occasion, I would like to be able to use a wider DSP setting with a narrower crystal filter, or a narrower DSP setting with a wider crystal filter.