K9YC's approach to pad the input so as to achieve better S/N into the
rig is great, but as Jim noted, with all knobs at eleven, the 3rd harmonic
was -24 dBc. Throttling back the sound card 3 dB brought it to -45 dBc
& with 6 dB back off, -60 dBc.
I suspect the typical amateur may not be aware of what those harmonics
can do & hitting the rig 20 dB harder to improve S/N with the pad means
that the harmonics are not necessarily 20 dB louder & therefore 20 dB
down after the pad.
Hum & noise is relatively easy for anyone to detect on the transmitted signal,
but other undesired artifacts may not be noticed or even register as a concern
with the typical amateur. Have a listen to some of the AFSK RTTY crowd on
the other bands & then extrapolate what the mess might be like should similar
obliviousness about how to set things up finds its way on 160 - all it takes
is one or two nasty signals to lay waste to quite a number of kcs of the
band... and on 160, it doesn't take much more degradation of C/N or C/I to
cause harmful interference to others.
I sure hope only those with a good grasp of this stuff tries the padding
route -
otherwise use an isolation transformer & a cleaner sound card.
73, VR2BrettGraham
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