K3: DSP NR for Data A mode?

[Bill Frantz]

Is it possible to implement Noise Reduction in the DSP for Data
A mode? Or is it a really stupid idea?

The PSK software I use -- cocoaModem for the Mac -- has a noise
reduction mode which works reasonably well when it is receiving
a broad spectrum signal -- 2 KHz or more. It does not work well
at all when I narrow the DSP bandwidth to eliminate strong
nearby signals. This situation leads to the annoying situation
where I can copy a weak station when the bandwidth is broad, but
not when I have narrowed it to eliminate strong nearby stations.
The strong nearby stations overload my SignaLink AtoD converter
which keeps me from copying the station. It seems to me the DSP
is in a position to apply noise reduction before the narrow band
filter, if that is the best way to perform noise reduction.

Cheers - Bill, AE6JV

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[phone]      | in a facility that processes   | 16345
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www.pwpconsult.com | peanuts and other nuts." - Duh | Los Gatos,
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[N5GE-2]

Have you tried using a narrower filter in the K3 or using the K3 NR?

Amateur Radio Operator N5GE
ARRL Lifetime Member
QCWA Lifetime Member

On Fri, 20 Jul 2012 09:03:20 -0700, Bill Frantz <[hidden email]> wrote:

>Is it possible to implement Noise Reduction in the DSP for Data
>A mode? Or is it a really stupid idea?
>
>The PSK software I use -- cocoaModem for the Mac -- has a noise
>reduction mode which works reasonably well when it is receiving
>a broad spectrum signal -- 2 KHz or more. It does not work well
>at all when I narrow the DSP bandwidth to eliminate strong
>nearby signals. This situation leads to the annoying situation
>where I can copy a weak station when the bandwidth is broad, but
>not when I have narrowed it to eliminate strong nearby stations.
>The strong nearby stations overload my SignaLink AtoD converter
>which keeps me from copying the station. It seems to me the DSP
>is in a position to apply noise reduction before the narrow band
>filter, if that is the best way to perform noise reduction.
>
>Cheers - Bill, AE6JV
>
>-------------------------------------------------------------------------
>Bill Frantz        | Airline peanut bag: "Produced  | Periwinkle
>[phone]      | in a facility that processes   | 16345
>Englewood Ave
>www.pwpconsult.com | peanuts and other nuts." - Duh | Los Gatos,
>CA 95032
>
>______________________________________________________________
>Elecraft mailing list
>Home: http://mailman.qth.net/mailman/listinfo/elecraft
>Help: http://mailman.qth.net/mmfaq.htm
>Post: mailto:[hidden email]
>
>This list hosted by: http://www.qsl.net
>Please help support this email list: http://www.qsl.net/donate.html

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[Bill Frantz]

Note that NR is not available in DATA A mode -- K3 manual p25:
"NR turns noise reduction on. It doesn’t apply to DATA or FM
modes, or with AGC turned off."

Ray identified why I would like the K3 NR to work in DATA A when
he said, "NR algorithms -need- a broad "chunk" of spectrum". If
the DSP NR could work on a broad spectrum before filtering it
would have enough data to separate signal from noise. I'm not
trying to get NR to deal with strong nearby signals, but when I
narrow the bandwidth to get rid of them, my post-narrowing NR no
longer works so I'm looking for pre-narrowing NR.

I have used the notch filter, but it takes time to deploy, and
can't deal with two separate loud signals. By experience,
narrowing the DSP bandwidth is operationally easier and more effective.

I suppose I should bite the bullet and get a 24 bit USB "sound
card". Does anyone have any recommendations?

[It hurts to spend money for a 24 bit A/D converter which is
going to convert analog the radio has produced using a 24 bit
D/A converter. It's just unaesthetic.]

Cheers - Bill, AE6JV

On 7/20/12 at 10:43, [hidden email] (N5GE) wrote:

>Have you tried using a narrower filter in the K3 or using the K3 NR?

On 7/20/12 at 11:11, [hidden email] (Ray Sills) wrote:

>Well, the way I see it.... Noise Reduction won't help you get
>rid of strong nearby (in frequency and/or QTH) signals.  That
>would be the job of a notch filter.  In fact, I think NR
>algorithms -need- a broad "chunk" of spectrum, so as to be able
>to identify what is "signal" and what is "noise".  If you
>narrow the DSP bandwidth, the software many not have enough
>noise to work with.
>
>If those strong signals are overloading the A/D converter, you
>would be better off lowering the level fed to the converter.  I
>think the SignaLink uses a 16 bit converter, and this is where
>a 24 bit converter would work much better, since it has 24 dB
>more dynamic range (before clipping).

-----------------------------------------------------------------------
Bill Frantz        | "The only thing we have to   | Periwinkle
[phone]      | fear is fear itself." - FDR  | 16345
Englewood Ave
www.pwpconsult.com | Inaugural address, 3/4/1933  | Los Gatos,
CA 95032

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[Don Wilhelm-4]

Bill,

I have not found 24 bit soundcards to be a requirement for data modes.  
16 bit soundcards will do just fine.

Yes, NR is not available in Data modes because it distorts the signal
and would result in reduced copy"ability".  The object is to produce as
clean a signal as possible to the soundcard.

What you observed is a true consequence of how most noise reduction
algorithms work.  They assume that the noise is distributed evenly
across the bandwidth they are receiving, and configure a filter to
reduce that noise.  If you narrow the bandwidth, that noise begins to
appear (to the mathematics) more and more like a signal that should not
be interfered with.

I would suggest that the best solution is to allow the data mode
software to sort things out to the best of its ability.  If you reduce
the signal width sufficiently to "home in" to the desired signal, then I
would expect the data software to be able to decode properly (at its
limits of rejection) using a wide bandwidth, and also be able to decode
quite well with a very narrow bandwidth, but at intermediate widths, the
datamode application software will not have enough bandwidth to properly
discern what is noise and which is a proper signal.

The noise reduction in many data mode applications is actually quite
good.  So my suggestion is to allow that data mode application to use
its noise reduction capability (which requires a wide bandwidth), but if
you are struggling to receive a signal, narrow the RX bandwidth to the
narrowest possible and see if the QSO can continue.

73,
Don W3FPR


On 7/20/2012 5:57 PM, Bill Frantz wrote:

> Note that NR is not available in DATA A mode -- K3 manual p25:
> "NR turns noise reduction on. It doesn’t apply to DATA or FM
> modes, or with AGC turned off."
>
> Ray identified why I would like the K3 NR to work in DATA A when
> he said, "NR algorithms -need- a broad "chunk" of spectrum". If
> the DSP NR could work on a broad spectrum before filtering it
> would have enough data to separate signal from noise. I'm not
> trying to get NR to deal with strong nearby signals, but when I
> narrow the bandwidth to get rid of them, my post-narrowing NR no
> longer works so I'm looking for pre-narrowing NR.
>
> I have used the notch filter, but it takes time to deploy, and
> can't deal with two separate loud signals. By experience,
> narrowing the DSP bandwidth is operationally easier and more effective.
>
> I suppose I should bite the bullet and get a 24 bit USB "sound
> card". Does anyone have any recommendations?
>
> [It hurts to spend money for a 24 bit A/D converter which is
> going to convert analog the radio has produced using a 24 bit
> D/A converter. It's just unaesthetic.]
>
> Cheers - Bill, AE6JV
>
> On 7/20/12 at 10:43, [hidden email] (N5GE) wrote:
>
>> Have you tried using a narrower filter in the K3 or using the K3 NR?
> On 7/20/12 at 11:11, [hidden email] (Ray Sills) wrote:
>
>> Well, the way I see it.... Noise Reduction won't help you get
>> rid of strong nearby (in frequency and/or QTH) signals.  That
>> would be the job of a notch filter.  In fact, I think NR
>> algorithms -need- a broad "chunk" of spectrum, so as to be able
>> to identify what is "signal" and what is "noise".  If you
>> narrow the DSP bandwidth, the software many not have enough
>> noise to work with.
>>
>> If those strong signals are overloading the A/D converter, you
>> would be better off lowering the level fed to the converter.  I
>> think the SignaLink uses a 16 bit converter, and this is where
>> a 24 bit converter would work much better, since it has 24 dB
>> more dynamic range (before clipping).
> -----------------------------------------------------------------------
> Bill Frantz        | "The only thing we have to   | Periwinkle
> [phone]      | fear is fear itself." - FDR  | 16345
> Englewood Ave
> www.pwpconsult.com | Inaugural address, 3/4/1933  | Los Gatos,
> CA 95032
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

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