K3S DSP filter plots

[charles-2]

 

Thanks for the reply Joe.

I'm hoping that the constant slope you described is not the way the DSP
filters are implemented, because that would mean the 50hz filter has a
5.625:1 shape factor, the the 100hz filter has a 5:1 shape factor, the
200 hz filter has a 3:1 shape factor and the 400hz filter would have a
2:1 shape factor. To achieve better than 2:1 shape factor at 30dB per
100hz, the width of the DSP filter would need to exceed 400hz.

I wonder if anyone has put their K3 or K3S in the 1 hz tuning mode with
a signal generator and ploted out the approximate response curves using
the S meter. It's a rather crude way to do it, but in the absence of
more accurate test gear it will give some idea of the shape factor of
the DSP filters.

I will be ordering a K3S today and will ask Elecraft if they have plots
for the 50, 100, 150, and 200 hz DSP filters. If not, I will get the
little signal generator and report my findings on the reflector.

If anyone reading this thread has plotted out the 50, 100, 150, or 200
hz DSP filter response curves, please let me know.

Charles K5UA

 
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[Don Wilhelm-4]

Charles,

Getting a plot is not difficult to do.  Just connect an audio spectrum
analyzer such as Spectrogram or SpectrumLab to the audio output of the
K3 and feed the antenna input with a broadband noise generator.
I use that technique most every day when aligning the IF filters on K2s
- quick and easy.

No I do not have any saved plots.

73,
Don W3FPR

On 11/16/2015 10:59 AM, [hidden email] wrote:

>  
>
> Thanks for the reply Joe.
>
> I'm hoping that the constant slope you described is not the way the DSP
> filters are implemented, because that would mean the 50hz filter has a
> 5.625:1 shape factor, the the 100hz filter has a 5:1 shape factor, the
> 200 hz filter has a 3:1 shape factor and the 400hz filter would have a
> 2:1 shape factor. To achieve better than 2:1 shape factor at 30dB per
> 100hz, the width of the DSP filter would need to exceed 400hz.
>
> I wonder if anyone has put their K3 or K3S in the 1 hz tuning mode with
> a signal generator and ploted out the approximate response curves using
> the S meter. It's a rather crude way to do it, but in the absence of
> more accurate test gear it will give some idea of the shape factor of
> the DSP filters.
>
> I will be ordering a K3S today and will ask Elecraft if they have plots
> for the 50, 100, 150, and 200 hz DSP filters. If not, I will get the
> little signal generator and report my findings on the reflector.
>
> If anyone reading this thread has plotted out the 50, 100, 150, or 200
> hz DSP filter response curves, please let me know.
>
>

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[David Woolley (E.L)]

Having a constant slope makes a lot of engineering sense.  I believe, at
least at some bandwidths, the K3 offers both IIR and FIR (infinite and
finite impulse response filters).  For data modes, FIR filters are
better, as they are linear phase filters.  The skirt slope of such a
filter is directly proportional to the number of taps used in the filter
(the number of old samples added together).  Having a large number of
taps increases the processing load on the DSP, so will be limited by the
need to work within the processing power of the DSP device.  Also longer
filters mean larger group delays.

IIR's have variable group delays and ring, but can produce responses
that could only be approximated by very long FIR filters.

Incidentally, merging the roofing and DSP filter edges is likely to
compromise the good group delay, and lack of ringing, characteristics of
the FIR filters.

--
David Woolley
Owner K2 06123


On 16/11/15 15:59, [hidden email] wrote:
> I'm hoping that the constant slope you described is not the way the DSP
> filters are implemented, because that would mean the 50hz filter has a
> 5.625:1 shape factor, the the 100hz filter has a 5:1 shape factor, the
> 200 hz filter has a 3:1 shape factor and the 400hz filter would have a
> 2:1 shape factor. To achieve better than 2:1 shape factor at 30dB per

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