[Elecraft] PSK31 -- ghost image:

[Rich Lentz]

Agreed, with a high quality soundcard the majority of any (all?) ghosts
would be caused by overdriving the sound card.

However, that does not explain the phenomena that I have observed with =
my
built-in (chip on motherboard) sound card and other inexpensive =
soundcards.
And I am looking at a ghost with the volume cranked down to the point =
the
main trace is barely readable right now.  For me this usually occurs =
during
high traffic periods and when the tones are at certain combinations of
frequencies.  Rarely does it happen when there is only one or two =
signals.=20

Do a search on "high fidelity digital audio conversion"  ( or this =
concept)
on the internet.  You will find some interfaces that cost any where from
$500 to $2500 with specifications as to their quality and statements =
that
"no oversampling is used."  With frequency responses up to 40 to 50 kHz. =
To
do that the sample rate must be no less than twice that - 64, 88.2, & 96 =
kHz
sample rates (higher if you want to pay MORE.  These interfaces also =
provide
32, 64, 128, and higher bit in the AD / DA converter.=20

Now look at the average PC soundcard and the PSK programs - digipan, =
MixW,
and the others.  They are using 11025 Hz sample-rate. (And few go up to =
32
bit DAC.) That is just over twice the bandwidth displayed and about four
times the K2 BW.  That means that a 5 kHz tone is a stepped square-wave =
and
a 2 kHz tone is smoother.  Speakers/headphones don't care - but digital
displays don't lie - and show all of the artifacts.

Rich
KE0X


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