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" <[email protected]> > To: <[email protected]> > 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:[email protected] >> >> 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:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ------------------------------------------------------------------------ > > > No virus found in this incoming message. > Checked by AVG - www.avg.com > Version: 8.0.237 / Virus Database: 270.11.5/1979 - Release Date: 03/01/09 > 17:46:00 > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
