[Elecraft] Roofing filters and DSP bandwidth tuning

[Fred Jensen]

True.  Statement was focused on preventing AGC action from signals 
outside the DSP BW and to do that, you'd like the roofing filters to 
include the DSP BW but not much more.  The "effective" BW of the xtal 
filters is also something larger than the 2.5 kHz or 0.5 kHz or 0.25 kHz 
in the name ... more poles = steeper skirts. Phase response is fairly 
irrelevant on CW and almost so on SSB.  If you're operating digital 
modes, phase response [and passband ripple] becomes important if the 
desired signal BW fills the filter BW.

73,

Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

On 1/27/2021 3:06 PM, David Woolley wrote:
> On 27/01/2021 20:35, Fred Jensen wrote:
>>    It follows that you'd probably like the selection of roofing 
>> filters to follow the DSP BW as closely as possible.
>
> Having the roofing filter too close to the DSP filter is not 
> necessarily a good thing, as the roofing filters are likely to have 
> worse passband ripples and will have non-linear phase responses, which 
> can compromise digital modes.  At least some of the DSP filters are 
> finite impulse response, meaning they are also linear phase, which 
> means that pulses will not get smeared out.
>