[Elecraft] [K2] question about crystal filters and DSP audio filter settings

[Kevin]

Thanks to Don and Robert for the quick and thorough responses about setting up the DSP filters. I will experiment with the settings now that I understand a little bit better. 


On Jan 30, 2013, at 8:57 PM, Don Wilhelm wrote:

> Kevin,
> 
> Usually the KDSP default filter widths work fine,  I would suggest that you leave CW AFIL1 set for LoPass and normally use the IF filters for general use.  When you encounter QRM, then first narrow the IF filter, and then if still needed, start down the AFIL steps to resolve the signal.
> In other words, there is only marginal benefit in using a 150 Hz KDSP2 bandwidth if your IF filter is set to 1.5 or 0.7 kHz.  The offending strong signal will still take over the K2 AGC and you will hear 'pumping' because the strong offending signal is controlling the AGC.
> 
> The KDSP2 filter skirts are steeper than the IF crystal filter skirts, and that is the main advantage.
> Narrower bandwidth is not always the best cure, but the choices are entirely yours to make.  Experiment a bit while listening to DX Pileups or during a "hot and heavy" contest where the bands are crowded, and that experience will give you the information you need to set the KDSP filters the way they will be of the most advantage to you.  Your current setting may be quite adequate.
> Your goal should be twofold - first is to reduce QRM from adjacent signals, and the second is to be able to pull weak signals out of a crowded band.  More narrow filter widths are not always the way to make that happen, but escaping from QRM with steeper filter skirts may work better.  A lot depends on your tuning skill as well as selection of the proper filters and the best way to develop that skill is to try it out on crowded band conditions.
> 
> It may be that you simply want to set the KDSP bandwidth to the same widths as the IF filters to take advantage of the steeper skirts. In other words, use AFIL2 in conjunction with IF FL2, AFIL3 in conjunction with IF FL3, etc.  It is rare that you will need less than 200 Hz of filter width, but YMMV.
> 
> 73,
> Don W3FPR
> 
>