[Elecraft] K3 XFIL Button

[Vic Rosenthal]

The XFIL button is my least favorite feature of the K3 user interface.
I always use the knob to change the bandwidth — except when I accidentally don’t hold the button long enough when activating or deactivating the APF, which I do a lot.

Victor 4X6GP 

> On 21 Feb 2019, at 13:40, Ed G <ed.n3cw at gmail.com> wrote:
> 
> Thanks Don.  I will have to experiement more using the DUAL PB. I have that button set up for APF right now.
> --Ed—
> 
> 
> Sent from Mail for Windows 10
> 
> From: Don Wilhelm
> Sent: Wednesday, February 20, 2019 6:00 PM
> To: Ed G; elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K3 XFIL Button
> 
> 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