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[K3] Manual Notch Reconsidered

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Dick Dickinson

[K3] Manual Notch Reconsidered

A recent post mentioned that the frequency and bandwidth of the K3 notch
could be controlled. If the bandwidth of the manual notch can be
controlled, I am unaware of how to go about it. I've found it broader than
I think it needs to be. I recall seeing it applied to an SSTV waterfall and
it was 100Hz wide (or wider?) with a flat bottom.

We've been talking about some features that may not be quite what we like
them to be. I got a good compliment on the K3 VOX in the past couple of
days.no clipping of the startup of VOX whatsoever. As well, there are a lot
of stations that could benefit from the type noise gate the K3 uses.

73,

Dick - KA5KKT

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Guy Olinger K2AV

Re: [K3] Manual Notch Reconsidered

Page 25 in "K3 Owner's man D10.pdf"

Available in the download section of the Elecraft web page.

Get the latest Adobe Reader to view the .pdf file. CTRL-F will bring
up a search window upper right corner of the Reader. Helps to make
quick searches in large .pdf documents which would sometimes be murder
in a paper version. Also finds things in Elecraft schematic diagram
.pdf files.

73, Guy

On Fri, Aug 1, 2014 at 1:10 AM, Dick Dickinson <[hidden email]> wrote:

> A recent post mentioned that the frequency and bandwidth of the K3 notch
> could be controlled. If the bandwidth of the manual notch can be
> controlled, I am unaware of how to go about it. I've found it broader than
> I think it needs to be. I recall seeing it applied to an SSTV waterfall and
> it was 100Hz wide (or wider?) with a flat bottom.
>
>
>
> We've been talking about some features that may not be quite what we like
> them to be. I got a good compliment on the K3 VOX in the past couple of
> days.no clipping of the startup of VOX whatsoever. As well, there are a lot
> of stations that could benefit from the type noise gate the K3 uses.
>
>
>
> 73,
>
> Dick - KA5KKT
>
>
>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

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Grant Youngman

Re: [K3] Manual Notch Reconsidered

It is possible to adjust the CENTER frequency. I’m unaware of any way to change the notch bandwidth.

Grant NQ5T

On Aug 1, 2014, at 12:29 AM, Guy Olinger K2AV <[hidden email]> wrote:

> Page 25 in "K3 Owner's man D10.pdf"
>
> Available in the download section of the Elecraft web page.
>
>
> On Fri, Aug 1, 2014 at 1:10 AM, Dick Dickinson <[hidden email]> wrote:
>> A recent post mentioned that the frequency and bandwidth of the K3 notch
>> could be controlled. If the bandwidth of the manual notch can be
>> controlled, I am unaware of how to go about it.
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Jim Brown-10

Re: [K3] Manual Notch Reconsidered

In reply to this post by Dick Dickinson

I have no clue what the K3 does, but the slickest way to do this is to
first sense the frequency of the tone you want to notch, then create a
tone of the same frequency, shift its phase so that it is exactly 180
degrees out of phase with the interfering tone, make it equal to the
interfering tone's amplitude, and add it to the signal. That will cancel
the tone with no other effect on the signal. That ain't easy, because it
must track the drift of both the TX and the RX and the varying strength
of the interfering signal, but with DSP, it IS possible. The beauty of
this technique is that it has NO effect on the desired signal -- it
simply cancels the interfering carrier.

The alternative technique is to add a narrow band notch filter, which
MUST add phase shift that distorts the audio. The deeper the notch and
the narrower the filter, the greater the phase shift, and thus greater
distortion of the signal.

These are fundamental concepts -- as my friends back home used to say,
"you cain't get no better" than this, :) and you must be very good
(and have the processor cycles available) to do it well.

73, Jim K9YC
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gm3sek

Re: [K3] Manual Notch Reconsidered

For both manual and auto notch, the key seems to be to create two
identical streams of signal data and apply different DSP to each. Stream
1 is totally focused on extracting accurate information about the
interfering tones (frequency, amplitude, phase) regardless of any damage
it may do to the audio signal. The damaged audio signal from Stream 1 is
then thrown away. Instead, the tone information extracted from Stream 1
is applied very carefully to a 'clean copy' of the same data in Stream 2
to cancel the interference with minimal damage to the recovered audio.

73 from Ian GM3SEK

>-----Original Message-----
>From: Elecraft [mailto:[hidden email]] On Behalf Of
>Jim Brown
>Sent: 01 August 2014 09:11
>To: [hidden email]
>Subject: Re: [Elecraft] [K3] Manual Notch Reconsidered
>
>I have no clue what the K3 does, but the slickest way to do this is to
>first sense the frequency of the tone you want to notch, then create a
>tone of the same frequency, shift its phase so that it is exactly 180
>degrees out of phase with the interfering tone, make it equal to the
>interfering tone's amplitude, and add it to the signal. That will

cancel
>the tone with no other effect on the signal. That ain't easy, because
it

>must track the drift of both the TX and the RX and the varying strength
>of the interfering signal, but with DSP, it IS possible. The beauty of
>this technique is that it has NO effect on the desired signal -- it
>simply cancels the interfering carrier.
>
>The alternative technique is to add a narrow band notch filter, which
>MUST add phase shift that distorts the audio. The deeper the notch and
>the narrower the filter, the greater the phase shift, and thus greater
>distortion of the signal.
>
>These are fundamental concepts -- as my friends back home used to say,
>"you cain't get no better" than this, :) and you must be very good
>(and have the processor cycles available) to do it well.
>
>73, Jim K9YC