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K3 Audio out artifacts

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Mike Scott-7

K3 Audio out artifacts

I have been investigating audio artifacts in connection with the K3 AGC hold
experimental firmware. As a reminder, I live in a high noise area.

As part of the investigation I have been looking at both Line Out and
headphone audio using Spectrumlab on my PC.

I am finding substantial 60-hz contamination on headphone audio that I do
not see on Line Out.

On Line Out I see what looks like fairly clean audio with donor lines at
2400 Hz and 3600 Hz outside the rx filter pass band (1 KHz DSP filtering). I
presume these are the 40th and 60th harmonics of 60 Hz. They are 50 dB below
noise background noise.

With only a change of where I plug the PC audio cable (moving from Line Out
jack to rear headphone jack) the audio looks quite different.

Now I see a whole array of 60 Hz artifacts. The 3rd and 5th harmonics are
about equal to comfortable listening level audio. As I look higher in
frequency the harmonics generally reduce in level but only to about 20 dB
below comfortable audio listening level. There is also a broad artifact (300
Hz wide) at roughly 3300 Hz that is also 25 dB down.

The artifacts do not go away with reduced volume control settings but remain
a constant feature of headphone audio out at any setting.

Is there something about my test set up that I do not understand?
Does anybody else see contamination of headphone audio on their K3?
Could there be something wrong with my K3?
Could transformer coupling (Line Out) vs direct coupling (headphone) be
adding something to my test set up that I am not factoring into the problem?

I have never quite believed the audio of my K3 was like Wayne says it should
be but can make it better using slow AGC (separate post), I doubt that has
anything to do with the artifacts I see here.

Mike Scott - AE6WA
Tarzana, CA (DM04 / near LA)
NAQCC 3535
K3-100 #508 / KX1 #1311

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Jim Brown-10

Re: K3 Audio out artifacts

On Mon, 2 Mar 2009 09:36:20 -0800, Mike Scott wrote:

>Is there something about my test set up that I do not understand?

Yes. The hum is probably in your test setup. Check out my tutorial
on Ham Interfacing.

http://audiosystemsgroup.com/HamInterfacing.pdf

and the corresponding material in text form in Chapter 8 of

http://audiosystemsgroup.com/RFI-Ham.pdf

73,

Jim K9YC

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n6wg

Re: K3 Audio out artifacts

In reply to this post by Mike Scott-7

Hi Scott
Out of curiousity, on the headphone output, are
you running it directly into a sound card to
use SpectrumLab? Or do you have some amount
of resistive load on the audio output with measurement
across the load?
73, Bob N6WG

----- Original Message -----
From: "Mike Scott" <[hidden email]>
To: <[hidden email]>
Sent: Monday, March 02, 2009 9:36 AM
Subject: [Elecraft] K3 Audio out artifacts

>I have been investigating audio artifacts in connection with the K3 AGC
>hold
> experimental firmware. As a reminder, I live in a high noise area.
>
> As part of the investigation I have been looking at both Line Out and
> headphone audio using Spectrumlab on my PC.
>
> I am finding substantial 60-hz contamination on headphone audio that I do
> not see on Line Out.
>
> On Line Out I see what looks like fairly clean audio with donor lines at
> 2400 Hz and 3600 Hz outside the rx filter pass band (1 KHz DSP filtering).
> I
> presume these are the 40th and 60th harmonics of 60 Hz. They are 50 dB
> below
> noise background noise.
>
> With only a change of where I plug the PC audio cable (moving from Line
> Out
> jack to rear headphone jack) the audio looks quite different.
>
> Now I see a whole array of 60 Hz artifacts. The 3rd and 5th harmonics are
> about equal to comfortable listening level audio. As I look higher in
> frequency the harmonics generally reduce in level but only to about 20 dB
> below comfortable audio listening level. There is also a broad artifact
> (300
> Hz wide) at roughly 3300 Hz that is also 25 dB down.
>
> The artifacts do not go away with reduced volume control settings but
> remain
> a constant feature of headphone audio out at any setting.
>
> Is there something about my test set up that I do not understand?
> Does anybody else see contamination of headphone audio on their K3?
> Could there be something wrong with my K3?
> Could transformer coupling (Line Out) vs direct coupling (headphone) be
> adding something to my test set up that I am not factoring into the
> problem?
>
>
> I have never quite believed the audio of my K3 was like Wayne says it
> should
> be but can make it better using slow AGC (separate post), I doubt that has
> anything to do with the artifacts I see here.
>
>
> Mike Scott - AE6WA
> Tarzana, CA (DM04 / near LA)
> NAQCC 3535
> K3-100 #508 / KX1 #1311
>
>
>
> ______________________________________________________________
> 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

Mel

Re: K3 Audio out artifacts

Doing critical audio tests can be very demanding. Circulating currents and non common ground loops are particularly a problem. I have had to use a TOPAZ Ultra isolation line noise suppressor transformer to supply AC to both the UUT and the scope/spectrum analyser. This forces the ground loops out of the issue. I have used standard isolation transformer with some success. But to get down to the base noise floor you need to make sure everything is common. A good test is to turn the K3 off and connect the probe and look at the spectrum. You should not see any 60 Hz or children.

Mel, K6KBE

--- On Mon, 3/2/09, Bob Tellefsen <[hidden email]> wrote:
From: Bob Tellefsen <[hidden email]>
Subject: Re: [Elecraft] K3 Audio out artifacts
To: [hidden email], [hidden email]
Date: Monday, March 2, 2009, 3:28 PM

Hi Scott
Out of curiousity, on the headphone output, are
you running it directly into a sound card to
use SpectrumLab? Or do you have some amount
of resistive load on the audio output with measurement
across the load?
73, Bob N6WG

----- Original Message -----
From: "Mike Scott" <[hidden email]>
To: <[hidden email]>
Sent: Monday, March 02, 2009 9:36 AM
Subject: [Elecraft] K3 Audio out artifacts

> I
> presume these are the 40th and 60th harmonics of 60 Hz. They are 50 dB
> below
> noise background noise.
>
> With only a change of where I plug the PC audio cable (moving from Line
> Out
> jack to rear headphone jack) the audio looks quite different.
>
> Now I see a whole array of 60 Hz artifacts. The 3rd and 5th harmonics are
> about equal to comfortable listening level audio. As I look higher in
> frequency the harmonics generally reduce in level but only to about 20 dB
> below comfortable audio listening level. There is also a broad artifact
> (300
> Hz wide) at roughly 3300 Hz that is also 25 dB down.
>
> The artifacts do not go away with reduced volume control settings but
> remain
> a constant feature of headphone audio out at any setting.
>
> Is there something about my test set up that I do not understand?
> Does anybody else see contamination of headphone audio on their K3?
> Could there be something wrong with my K3?
> Could transformer coupling (Line Out) vs direct coupling (headphone) be
> adding something to my test set up that I am not factoring into the
> problem?
>
>
> I have never quite believed the audio of my K3 was like Wayne says it
> should
> be but can make it better using slow AGC (separate post), I doubt that has
> anything to do with the artifacts I see here.
>
>
> Mike Scott - AE6WA
> Tarzana, CA (DM04 / near LA)
> NAQCC 3535
> K3-100 #508 / KX1 #1311
>
>
>
> ______________________________________________________________
> 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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Don Wilhelm-4

Re: K3 Audio out artifacts

In reply to this post by n6wg

Mike,

Contrary to popular myth --
There is no need for any kind of resistive loading at the headphone
output. A low impedance source (the amplifier in the K3) feeding a high
impedance input (the soundcard) works as it should for spectral analysis.
.
If you were measuring available power output from the headphone jack,
then load termination would become important.

73,
Don W3FPR

Bob Tellefsen wrote:

> Hi Scott
> Out of curiousity, on the headphone output, are
> you running it directly into a sound card to
> use SpectrumLab? Or do you have some amount
> of resistive load on the audio output with measurement
> across the load?
> 73, Bob N6WG
>
> ----- Original Message -----
> From: "Mike Scott" <[hidden email]>
> To: <[hidden email]>
> Sent: Monday, March 02, 2009 9:36 AM
> Subject: [Elecraft] K3 Audio out artifacts
>
>
>
>> I have been investigating audio artifacts in connection with the K3 AGC
>> hold
>> experimental firmware. As a reminder, I live in a high noise area.
>>
>> As part of the investigation I have been looking at both Line Out and
>> headphone audio using Spectrumlab on my PC.
>>
>> I am finding substantial 60-hz contamination on headphone audio that I do
>> not see on Line Out.
>>
>> On Line Out I see what looks like fairly clean audio with donor lines at
>> 2400 Hz and 3600 Hz outside the rx filter pass band (1 KHz DSP filtering).
>> I
>> presume these are the 40th and 60th harmonics of 60 Hz. They are 50 dB
>> below
>> noise background noise.
>>
>> With only a change of where I plug the PC audio cable (moving from Line
>> Out
>> jack to rear headphone jack) the audio looks quite different.
>>
>> Now I see a whole array of 60 Hz artifacts. The 3rd and 5th harmonics are
>> about equal to comfortable listening level audio. As I look higher in
>> frequency the harmonics generally reduce in level but only to about 20 dB
>> below comfortable audio listening level. There is also a broad artifact
>> (300
>> Hz wide) at roughly 3300 Hz that is also 25 dB down.
>>
>> The artifacts do not go away with reduced volume control settings but
>> remain
>> a constant feature of headphone audio out at any setting.
>>
>> Is there something about my test set up that I do not understand?
>> Does anybody else see contamination of headphone audio on their K3?
>> Could there be something wrong with my K3?
>> Could transformer coupling (Line Out) vs direct coupling (headphone) be
>> adding something to my test set up that I am not factoring into the
>> problem?
>>
>>
>> I have never quite believed the audio of my K3 was like Wayne says it
>> should
>> be but can make it better using slow AGC (separate post), I doubt that has
>> anything to do with the artifacts I see here.
>>
>>
>> Mike Scott - AE6WA
>> Tarzana, CA (DM04 / near LA)
>> NAQCC 3535
>> K3-100 #508 / KX1 #1311
>>
>>
>>
>> ______________________________________________________________
>> 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/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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