[Elecraft] PSK31 -- ghost image:

[Jim W7RY]

No.
Ghosts are created by the sound card OVERDRIVING the radio of the person
that has the ghost.

It's that simple. Ghosts have been a problem LONG before sound cards were
even thought of. Long before personal computers were even thought of.

I have been in RTTY for 25 years.

73, Jim
W7RY


----- Original Message -----
From: "Rich Lentz" <ke0zx@cox.net>
To: <w5yr@att.net>
Cc: "Elecraft Reflector" <elecraft@mailman.qth.net>
Sent: Friday, February 14, 2003 5:23 PM
Subject: RE: [Elecraft] PSK31 -- ghost image:


> 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.
>
> 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.
>
> 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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