Re: K3S Crystal Filtering


Bob Novas
 

Jim - yes, but... That is the question - at similar bandwidths, are the
digital filters implemented in the K3S ones that have better phase shift
characteristics than the crystal filters that have a known phase shift
characteristic and would be beneficial to use the DSP filters in preference
to the narrow bandwidth crystal filters, in situations that don't need tight
roofing. For example, a DX pileup, with weak to moderate signals and no
very strong signals. The devil is in the details. Bob - W3DK

-----Original Message-----
From: Elecraft-K3@groups.io [mailto:Elecraft-K3@groups.io] On Behalf Of Jim
Brown
Sent: Sunday, February 14, 2021 11:49 PM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] K3S Crystal Filtering

It isn't only hardware filters that have the phase shift -- DSP filters
use the math that describes the performance of hardware filters. There
is a class of DSP filters that don't have the phase shift problem, but
they have greater latency and, I believe, require more processing power.

And because of the interrelationship of phase, frequency, and time, the
effect of the phase shift is that the different frequencies that make up
a waveform take more or less time get through the filter, so the signal
is "smeared" in time.

The same thing happens in transmission lines at low frequencies --
indeed, equalization was developed in the earliest days of telephony
(and telegraphy) because both the loss AND the velocity of propagation
were changing dramatically at audio frequencies; without equalization,
on long distance circuits, the high audio frequencies would arrive long
before the lows, so speech would be unintelligible!

73, Jim K9YC

On 2/13/2021 7:24 AM, Bob Novas via groups.io wrote:
After hearing Eric talk about the K4 filtering
(https://www.youtube.com/watch?v=OoMoJddbFyI&t=1221s
<https://www.youtube.com/watch?v=OoMoJddbFyI&t=1221s>) and the phase
shift problems with narrow crystal filters, I wondered if you could run
the K3S with wide crystal filters and narrow DSP filters at times when
you don’t need tight roofing filtering.  And, if you did that, would
that improve the situation with respect to muddy audio when listening to
highly filtered speech.

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