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.
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