DSP & XTAL filter settings?

[Solosko, Robert B (Bob)-2]

Hello All,

        I just added the DSP processor to my K2 and adjusted both the DSP and XTAL filters to the same center frequency using Spectrogram. The DSP and XTAL filters work fine together, except that when using the default filter settings, the DSP and XTAL filters essentially duplicate each other and it's not obvious what the best combination of filter settings should be and how the XTAL and DSP filters should be used in combination, particularly for SSB.

        I found a posting from Tom Hammond from January in which he recommends that for CW, because of the signal loss of the XTAL filters below 200Hz, use the DSP filters below 200 Hz. and the XTAL filters above 200 Hz. Thus, it seems that I should set the CW DSP filters to something like 200 Hz, 100 Hz, 50 Hz and LOPASS, and the XTAL CW filters to something like 1.5 kHz, 1.0 kHz, 700 Hz and 400 Hz.  Then, when I want the wider bandwidth, I'd use one of the XTAL filters with the DSP filter set to LOPASS, and when I want the narrower bandwidth, I'd use one of the DSP filters (and since the XTAL filters all would have wider bandwidths, it wouldn't make any difference which XTAL filter is selected).

        That seems like a reasonable approach to the DSP and XTAL filter settings and combinations on CW. (Comments?)

        However, I have no idea how to set up the DSP and XTAL filters and what filter combinations to use for SSB. It seems to be a waste of the K2 capabilities just to have the DSP and XTAL SSB filters essentially duplicate each other, as their default settings seem to do. So, is there some optimum way to setup the DSP and XTAL filters and use them in combination for SSB that makes best use of the K2 capabilities?

        Thanks for any advice and suggestions that you can give me.


Bob Solosko
W1SRB
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[Dan Barker]

It's still going to matter, if you are running AGC or there are strong
nearby signals. Run your CW filter at 400Hz for any narrower DSP setting.

Dan / WG4S / K2 #2456

<snip>
Then, when I want the wider bandwidth, I'd use one of the XTAL filters with
the DSP filter set to LOPASS, and when I want the narrower bandwidth, I'd
use one of the DSP filters (and since the XTAL filters all would have wider
bandwidths,

_it wouldn't make any difference which XTAL filter is selected_ [emphasis
added]

).
</snip>

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[w6jd]

My preference is to use the 700 Hz xtal filter and then narrow down the bandwidth with the DSP filters when necessary.

Doug, W6JD
K2/100 #1626

-------------- Original message --------------
From: "Solosko, Robert B (Bob)" <[hidden email]>

>
> Hello All,
>
> I just added the DSP processor to my K2 and adjusted both the DSP and
> XTAL filters to the same center frequency using Spectrogram. The DSP and XTAL
> filters work fine together, except that when using the default filter settings,
> the DSP and XTAL filters essentially duplicate each other and it's not obvious
> what the best combination of filter settings should be and how the XTAL and DSP
> filters should be used in combination, particularly for SSB.
>
> I found a posting from Tom Hammond from January in which he recommends
> that for CW, because of the signal loss of the XTAL filters below 200Hz, use the
> DSP filters below 200 Hz. and the XTAL filters above 200 Hz. Thus, it seems that
> I should set the CW DSP filters to something like 200 Hz, 100 Hz, 50 Hz and
> LOPASS, and the XTAL CW filters to something like 1.5 kHz, 1.0 kHz, 700 Hz and
> 400 Hz. Then, when I want the wider bandwidth, I'd use one of the XTAL filters
> with the DSP filter set to LOPASS, and when I want the narrower bandwidth, I'd
> use one of the DSP filters (and since the XTAL filters all would have wider
> bandwidths, it wouldn't make any difference which XTAL filter is selected).
>
> That seems like a reasonable approach to the DSP and XTAL filter
> settings and combinations on CW. (Comments?)
>
> However, I have no idea how to set up the DSP and XTAL filters and what
> filter combinations to use for SSB. It seems to be a waste of the K2
> capabilities just to have the DSP and XTAL SSB filters essentially duplicate
> each other, as their default settings seem to do. So, is there some optimum way
> to setup the DSP and XTAL filters and use them in combination for SSB that makes
> best use of the K2 capabilities?
>
> Thanks for any advice and suggestions that you can give me.
>
>
> Bob Solosko
> W1SRB
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[Bill Coleman-2]

On May 9, 2006, at 9:30 AM, Solosko, Robert B (Bob) wrote:

> Thus, it seems that I should set the CW DSP filters to something  
> like 200 Hz, 100 Hz, 50 Hz and LOPASS, and the XTAL CW filters to  
> something like 1.5 kHz, 1.0 kHz, 700 Hz and 400 Hz.  Then, when I  
> want the wider bandwidth, I'd use one of the XTAL filters with the  
> DSP filter set to LOPASS, and when I want the narrower bandwidth,  
> I'd use one of the DSP filters (and since the XTAL filters all  
> would have wider bandwidths, it wouldn't make any difference which  
> XTAL filter is selected).

One thing I would like in the K2 is a firmware change that would  
invoke a given XTAL and DSP filter combination. Certain DSP filter  
settings may not make sense when combined with other XTAL filters.

> However, I have no idea how to set up the DSP and XTAL filters and  
> what filter combinations to use for SSB. It seems to be a waste of  
> the K2 capabilities just to have the DSP and XTAL SSB filters  
> essentially duplicate each other, as their default settings seem to  
> do.

On SSB, there's basically one XTAL filter - OP1. The variable  
bandwidth filter is pretty asymmetric for use on SSB. OP1 also has a  
very modest shape factor.

I use the DSP filter to clean up the shape of the OP1 filter. I have  
a couple of variants programmed that cut the high and low end of the  
filter. These are useful during contests or any time there's lots of  
QRM. Narrowing the filter may slightly reduce intelligibility, but it  
also cuts adjacent signals.

> So, is there some optimum way to setup the DSP and XTAL filters and  
> use them in combination for SSB that makes best use of the K2  
> capabilities?

I have my DSP set up for LPASS, 200-2400, 300-2200, 300-2000 (I  
think). My K2 is a bit unusual as I have the "1.9" kHz SSB filter, as  
designed by KI6WX. This is similar to the original K2 SSB filter -  
about 2.0 kHz wide, but the caps have been modified to give a  
bandpass with less ripple.

Oh, and I leave the automatic notch filter on in SSB all the time.

Bill Coleman, AA4LR, PP-ASEL        Mail: [hidden email]
Quote: "Not within a thousand years will man ever fly!"
             -- Wilbur Wright, 1901

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[Don Wilhelm-3]

Bill and all,

I must disagree - when the SSB filter widths and corresponding BFOs are
correctly set, the variable XTAL filters can be quite usable for SSB
reception.

First of all, the lower -3dB frequency corner of the passband must be near
300 Hz to maintain intelligibility.  The high frequencies may be cut without
sacrificing a lot of intelligibility.  The filter width must be determined
by using Spectrogram or a similar means - the numbers given by the K2
display for the wide filter settings may be grossly in error (the actual
filter width is usually quite a bit wider than the numbers indicate at the
wider filter settings - it is close to actual at 400 to 500 Hz widths, which
is the design center for the filter).

If the SSB filters are set for FL1 = OP1, and FL2 thru FL3 are set for
progressively more narrow filters, then a properly tuned SSB signal will
remain intelligible as the filters are narrowed, and high frequency QRM will
be reduced.

Assuming the 2.4 kHz width is used for OP1, centering the filter passband
between the following Spectrogram markers will result in quite usable
filters:
FL1 width = OP1 -- 300 and 2600 Hz
FL2 measured width = 2200 Hz -- 300 and 2400 Hz
FL3 measured width - 2000 Hz -- 300 and 2200 Hz
FL4 measured width = 1800 Hz -- 300 and 2000 Hz

The DSP can be used as a supplement to these filters, but I find that the IF
filters are adequate in most cases, freeing the DSP to be used for noise
reduction and notch filtering purposes in SSB mode.

Again, I find the most prevalent 'error' in setting the variable filters for
SSB use is in assuming that the filter width is what is indicated on the K2
display - and that actual width may be quite a bit wider than indicated -
measure the width with the Spectrogram display and ignore the width numbers
shown in the display.

73,
Don W3FPR

> -----Original Message-----
>
>
> On SSB, there's basically one XTAL filter - OP1. The variable
> bandwidth filter is pretty asymmetric for use on SSB. OP1 also has a
> very modest shape factor.
>
> I use the DSP filter to clean up the shape of the OP1 filter. I have
> a couple of variants programmed that cut the high and low end of the
> filter. These are useful during contests or any time there's lots of
> QRM. Narrowing the filter may slightly reduce intelligibility, but it
> also cuts adjacent signals.
>
>

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