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DL4YHF@aol.com wrote:
<blockquote TYPE=CITE><font face="arial,helvetica"><font size=-1>Hello
group,</font></font>
<p><font face="arial,helvetica"><font size=-1>Because of the coming test
transmissions on 16kHz and 17.2kHz, I did a few</font></font>
<br><font face="arial,helvetica"><font size=-1>tests with 'direct reception'
of LF signals up to 20 kHz using only the PC, a</font></font>
<br><font face="arial,helvetica"><font size=-1>soundcard, a piece of software
and a few metres of wire. The results are</font></font>
<br><font face="arial,helvetica"><font size=-1>good, and may be useful
for some of you.</font></font>
<p><font face="arial,helvetica"><font size=-1>The basic concept:</font></font>
<br><font face="arial,helvetica"><font size=-1>- soundcard running at 44100
Hz sample rate</font></font>
<br><font face="arial,helvetica"><font size=-1>- input signal is converted
to 650Hz audio with an image-rejecting mixer</font></font>
<br><font face="arial,helvetica"><font size=-1> (phase method, using
a Hilbert transformer)</font></font>
<br><font face="arial,helvetica"><font size=-1>- output from the mixer
(650Hz) filtered with IIR or FIR filter,</font></font>
<br><font face="arial,helvetica"><font size=-1>100Hz bandwidth or less</font></font>
<br><font face="arial,helvetica"><font size=-1>- output from the filter
passed to soundcard output (in real-time).</font></font>
<br>
<p><font face="arial,helvetica"><font size=-1>You need a PC with at least
166MHz, Spectrum Lab V1.65 beta5 (new).</font></font>
<p><font face="arial,helvetica"><font size=-1>The problem is that not all
soundcards are suited for this "full duplex"</font></font>
<br><font face="arial,helvetica"><font size=-1>operation (or, to be precise,
the control program does not allow the proper</font></font>
<br><font face="arial,helvetica"><font size=-1>settings). I did a few tests
on some PC's, on two it worked immediately and</font></font>
<br><font face="arial,helvetica"><font size=-1>one (a notebook) had kind
of a 'feedback' problem.</font></font>
<br>
<p><font face="arial,helvetica"><font size=-1>More info can be found here:</font></font>
<br><font face="arial,helvetica"><font size=-1> <A HREF="http://www.qsl.net/dl4yhf/vlf_rcvr.html">http://www.qsl.net/dl4yhf/vlf_rcvr.html</A>
.</font></font>
<p><font face="arial,helvetica"><font size=-1>The 'special pre-release'
of Spectrum Lab V1.65 beta5 can be loaded from:</font></font>
<br><font face="arial,helvetica"><font size=-1> <A HREF="http://members.aol.com/dl4yhfhamsoft/spectr_i.zip">http://members.aol.com/dl4yhfhamsoft/spectr_i.zip</A></font></font>
<p><font face="arial,helvetica"><font size=-1>I am very interested in the
16kHz transmission from GBR, hope it's going to</font></font>
<br><font face="arial,helvetica"><font size=-1>work. Thanks for passing
the info about GBR, Mike.</font></font>
<p><font face="arial,helvetica"><font size=-1>User feedback welcome. Good
luck, cu on 136kHz,</font></font>
<br><font face="arial,helvetica"><font size=-1> 73's Wolf (DL4YHF,
DF0WD).</font></font></blockquote>
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