Re: CW narrow filter


ve3ki
 

You select the DSP bandwidth with the WIDTH control. This also automatically selects the roofing filter, based on the filter bandwidths you have entered into the filter configuration using either the K3 Utility or the CONFIG:FLx BW settings. If you have a roofing filter set to switch in at a particular width, it will be selected automatically at that DSP width and below. The FLx BW settings do not have to match the designation on the filter; you can set each roofing filter to be switched in at the bandwidth of your choice.

If you want to use narrow DSP settings using a wider roofing filter than the one that would normally switch in based on its designation, you need to go into the filter configuration and change the bandwidth at which the narrower roofing filter is selected. For example, if you have a 400 Hz roofing filter but you don't want it ti be selected at DSP bandwidths above 300 Hz, then in the CONFIG:FLx BW menu for the 400 Hz roofing filter, select 0.30 instead of 0.40. You can go the other way as well: if you have a 250 Hz roofing filter but you want it to be selected at 350 Hz and below, set CONFIG:FLx BW to 0.35 instead of 0.25.

73,
Rich VE3KI


On Tue, Nov 27, 2018 at 09:04 AM, David Box wrote:

Bob

How have you setup the filter selection on your K3?  When I use the XFIL button to change roofing filter the DSP bandwidth also increases.  Looking through the manual I don't see how you can set a roofing filter to stay fixed while changing to narrow DSP so know I am missing something, would like to minimize ringing by using as wide a roofing filter as I can.

de Dave K5MWR

On 11/26/2018 6:53 PM, Bob McGraw - K4TAX wrote:

And........very narrow filters, due to group delay, will take a noise pulse or spike and it will go SPLAT across the passband.   Hence the filter makes the spike much wider than the original width of the spike.    For the most part, random or broadband noise is unaffected.    Just opening up the passband to the point where the narrow filter switches out can make noticeable improvement in receiving conditions.   I prefer to use a narrow DSP passband and manually select a wider roofing filter.   My K3S makes for a super sweet receiver in this regard.

73

Bob, K4TAX

 


On 11/26/2018 6:23 PM, Jim English wrote:
The problem with very narrow CW filters is that they generally have very steep skirts which means the generally they have to be designed without regard to the group delay variation throughout the passband.  Most are based on Chebychev coefficients or some modification thereof.  As such, there is a significant amount of energy stored at the passband edges which cause ringing to be heard in the demodulated signal.  Receivers based on DSP in the signal processing stages generally don't suffer from this as the filters are a linear phase type that are constant group delay which do not have the ringing issue.  Where the AGC pickoff point is located may affect the performance but I must say that I love my (by now) old iron flex 5k transceiver.  Last month when everybody was trying to work the Ducie island station I had an issue where there was some lid operator QRMing.  However, he was close in frequency but not close enough.  I just cranked the bandwidth of the flex DSP filter down to about 50 Hz and that turkey was GONE.  Then I worked him of course.  I love my 5k so much that I bought a spare since they are nor being built anymore and are cheap now.  They do require a windows computer that can get out of its own way however and they are definitely not for the computer squeamish but getting past that I think they are the bomb!  The newer ones are probably better but being a HAM which stands for "haven't any money" I am too cheap to buy one.  At least now.
 
73,
 
Jim WO7V

On Mon, Nov 26, 2018 at 7:46 AM john ni0k <jasimmons@...> wrote:
Operating the CW WW CQ contest makes me wish for something narrower than
the 400 Hz filter in my rig currently. I know Elecraft has a 200 Hz
filter but is there something else that people are using?

73,
-John NI0K



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