[Elecraft] Question - for Educational Purposes

[Alan Bloom]

On Fri, 2008-07-25 at 00:09, David Woolley (E.L) wrote:

> FIR filters cannot ring in the full sense of the word.  What they can do 
> is to generate a finite pulse of a particular frequency, but that pulse 
> is never longer than the filter length.  Long filter lengths result in a 
> delay in the signal, which can become unacceptable in itself, so systems 
> are not designed with extremely long filters.

For signals received by the human ear, the filter length would have to
be really long to be objectionable.  For a symmetrical impulse response,
the delay is 1/2 the filter length.  For example, assuming a 10 kHz
sample rate and a 1000-tap filter, the delay is only 1/20 second. 

To get a decent shape factor, the filter length in seconds needs to be
at least a few times 1/bandwidth.  Say 10/BW or so, resulting in 5/BW
delay.  So even with a 50 Hz bandwidth, the delay only needs to be on
the order of 1/10 second.  I don't think you'd ever notice that in
normal on-the-air operation.

Al N1AL