[TenTec] NB verses NR
k9yc at audiosystemsgroup.com
Wed Dec 17 12:33:18 EST 2014
On Mon,12/15/2014 11:20 AM, Peter Bertini wrote:
> I do understand that the improved skirts will cause ringing on noise
> impulses, but I am living with that problem.
Ringing is the result of the SHAPE of the amplitude and phase response
of a system, including filters. Filter skirts are not "improved" if they
increase ringing on noise. Skirts are "improved" if they provide greater
rejection outside the passband while minimizing ringing.
The Elecraft K2 sounded very nice on RX when using the TX crystal
filter, but to narrow the SSB response, the multi-stage crystal filter
was realigned to stagger tune it, and the amplitude response looked like
a cross section of the Rockie mountains. The resulting distortion of
amplitude and phase made it painful to use.
Note that the K2 is an analog kit using discrete components, originally
designed as a 80-10M QRP CW rig, and expanded over several years to add
160M, SSB, AF DSP, and a 100W amp.
All filters are not created equal -- some mathematical shapes sound FAR
better than others. One of the great things about DSP is the ability of
a smart designer to optimize the shaping of both amplitude and phase
response. That sort of careful shaping is a large part of why the K3 CW
bandwidth is half that of its closest competitors.
73, Jim K9YC
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