[Elecraft] K3 filters

[n1al at cds1.net]

> I think you meant that they don't have group delay variations.

That's right, even FIR filters have group delay.  It's typically equal to
half the length (impulse response) of the filter.

> Actually I have a feeling that constant group delay is only true of
> finite impulse response filters.

Right, FIR filters with symmetrical coefficients (i.e. almost all of them)
are "linear phase" which means flat group delay.  That is, the delay
through the filter is independent of the frequency.  That is very
important for digital modulation and I believe it also makes SSB sound
more natural.

Al N1AL


> Benny Aumala wrote:
>>
>> DSP makes very steep  filters WIHOUT group delays.
>> K3 concentrates best selectivity here. Correct!
>>
> I think you meant that they don't have group delay variations.  They
> certainly have group delays; they work by adding together delayed
> versions of the signal.
>
> Actually I have a feeling that constant group delay is only true of
> finite impulse response filters.
>
> --
> David Woolley