[Elecraft] K3 Audio out artifacts

[Bob Tellefsen]

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" <mike at paxsen.com>
To: <Elecraft at mailman.qth.net>
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:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html