Posted by
Don Wilhelm-4 on
Jul 20, 2012; 10:33pm
URL: http://elecraft.85.s1.nabble.com/K3-DSP-NR-for-Data-A-mode-tp7559524p7559560.html
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
> (408)356-8506 | 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______________________________________________________________
Elecraft mailing list
Home:
http://mailman.qth.net/mailman/listinfo/elecraftHelp:
http://mailman.qth.net/mmfaq.htmPost: mailto:
[hidden email]
This list hosted by:
http://www.qsl.netPlease help support this email list:
http://www.qsl.net/donate.html