As others have stated, using the Line Out as a proxy for the headphone and/or
speaker outputs is probably not a good idea.
The only time it is valid is if you are using the Line Out into the same sound
card for digital modes.
Otherwise, if you are using headphones, you should be looking at the spectrum
with your 'phones plugged in. If you are using an external speaker then look
across it. If you are using the internal speaker, stop and avoid it like the
plague (unless you play electric guitar and like the sound of distortion).
The other caveat: avoid over-driving the sound card. Good lab practice when
making spectrum measurements with any instrument is to insert some attenuation
between the source and the analyzer and look at the effect. If you put in 10
dB and some product drops 20 dB, you have an issue.
Of course, all of this assumes that you have clean power supplies and no ground
loops adding line frequency spurs to your plot.
Wes N7WS
--- On Sun, 12/20/09, Julian, G4ILO <julian.g4...@gmail.com> wrote:
However - and this is the interesting bit - the level of the harmonics
relative to the fundamental can be varied by changing the LIN OUT level. On
my K3 reducing LIN OUT to 003 and they just about disappear. (Obviously that
also depends on the strength of the input signal.)
It seems to me that there is some non-linearity in the audio stages that
sets in at a fairly low level. I'm not an expert either, but might the
isolating transformers in the line output be the cause of this?
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