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<H1>WebSDR receiver on 20m, 40m and 80m</H1>
<P><FONT face=Verdana>The amateur radio club <STRONG>ETGD</STRONG> at the
University of Twente provide a <STRONG>WebSDR</STRONG> HF receiver for use by
Radio Amateurs and listeners around the world. </FONT></P>
<P><FONT face=Verdana>In contrast to other web-controlled receivers, this can be
tuned by multiple users simultaneously, thanks to the use of Software-Defined
Radio.</FONT></P>
<P><FONT face=Verdana>Tuning is done either by clicking or dragging with the
mouse on the waterfall display, by typing a frequency into the text box, or by
using the up/down buttons. The bandwidth can be changed by clicking the
appropriate buttons, and by 'dragging" the edges of the yellow passband
indication.</FONT></P>
<P><FONT face=Verdana>The present system consists of the following
hardware:</FONT></P>
<P><FONT face=Verdana>• A W3DZZ trap-dipole for the 80 and 40 meter amateur
radio bands, on top of the 40 m high "Hogekamp" building of the University of
Twente.</FONT></P>
<P><FONT face=Verdana>• Simple bandpass filters for the 80 m, 40 m and 20 m
bands.</FONT></P>
<P><FONT face=Verdana>• A quadrature mixer in which the signals are mixed with
about 7080.7 kHz. This mixer is a Quadrature Sampling Detector or "Tayloe
mixer", the well-known circuit with a four-position CMOS switch, which is also
used in many amateur radio SDR front-ends such as the SDR-1000 and the
SoftRock.</FONT></P>
<P><FONT face=Verdana>• Similar mixers operating at 3600 kHz and 14161
kHz.</FONT></P>
<P><FONT face=Verdana>• A PC with soundcards to receive and process the signals
coming out of the quadrature mixers. The PC is an old Pentium-III at 1 GHz,
running Linux and the WebSDR server software (written by PA3FWM).</FONT></P>
<P><FONT face=Verdana>To use the WebSDR HF radio receiver go to<BR></FONT><A
href="http://websdr.ewi.utwente.nl:8901/" target=_blank><FONT
face=Verdana>http://websdr.ewi.utwente.nl:8901/</FONT></A></P>
<P><FONT face=Verdana>PA3FWM's Software Defined Radio page<BR></FONT><A
href="http://wwwhome.cs.utwente.nl/~ptdeboer/ham/sdr/" target=_blank><FONT
face=Verdana>http://wwwhome.cs.utwente.nl/~ptdeboer/ham/sdr/</FONT></A>
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